micropython-micro-gui

This is a lightweight, portable, MicroPython GUI library for displays having drivers subclassed from framebuf. Written in Python it runs under a standard MicroPython firmware build. Options for data input comprise:

• Two pushbuttons: limited capabilities with some widgets unusable for input.
• Three pushbuttons with full capability.
• Five pushbuttons: full capability, less "modal" interface.
• A switch-based navigation joystick: another way to implement five buttons.
• Via two pushbuttons and a rotary encoder such as this one. An intuitive interface.
• On ESP32 physical buttons may be replaced with touchpads.

It is larger and more complex than nano-gui owing to the support for input. It enables switching between screens and launching modal windows. Widgets are a substantial superset of nano-gui widgets.

Supported displays

It is compatible with all display drivers for nano-gui so is portable to a wide range of displays. It is also portable between hosts.

Raspberry Pico with an ILI9341 from eBay.

TTGO T-Display. A joystick switch and an SIL resistor make a simple inexpensive and WiFi-capable system.

micro_gui now has limited support for ePaper.

Rationale

Touch GUI's have many advantages, however they have drawbacks, principally cost and the need for calibration (although the official LCD160cr is factory calibrated). Another problem is that there are various types of touch controller, magnifying the difficulty of writing a portable GUI.

The input options work well and yield astonishingly low cost solutions. A network-connected board with a 135x240 color display can be built for under £20 ($20?) using the TTGO T-Display. The test board shown above has a 320x240 display from eBay with a Pi Pico and has a component cost of well below £20.

The following are similar GUI repos with differing objectives.

• nano-gui Extremely low RAM usage but display-only with no provision for input.
• LCD160cr Touch GUI for the official display.
• RA8875 Touch GUI for displays with RA8875 controller. Supports large displays, e.g. from Adafruit.
• SSD1963 Touch GUI for displays based on SSD1963 and XPT2046. High performance on large displays due to the parallel interface. Specific to STM hosts.

LVGL is a pretty icon-based GUI library. It is written in C with MicroPython bindings; consequently it requires the build system for your target and a C device driver (unless you can acquire a suitable binary).

Project status

April 2023: Add limited ePaper support, grid widget, calendar and epaper demos. Now requires firmware >= V1.20.

July 2022: Add ESP32 touch pad support.

June 2022: Add QRMap and BitMap widgets.

March 2022: Add latency control for hosts with SPIRAM.

February 2022: Supports use with only three buttons devised by Bart Cerneels. Simplified widget import. Existing users should replace the entire gui tree.

Code has been tested on ESP32, ESP32-S2, ESP32-S3, Pi Pico and Pyboard. This is under development so check for updates.

0. Contents

1. Basic concepts Including "Hello world" script.
   1.1 Coordinates The GUI's coordinate system.
   1.2 Screen Window and Widget objects Basic GUI classes.
   1.3 Fonts
   1.4 Navigation How the GUI navigates between widgets.
   1.5 Hardware definition How to configure your hardware.
   1.6 Quick hardware check Testing the hardware config. Please do this first.
   1.7 Installation Installing the library.
   1.8 Performance and hardware notes
   1.9 Firmware and dependencies
   1.10 Supported hosts and displays
   1.11 Files Discussion of the files in the library.
        1.11.1 Demos Simple demos showing coding techniques.
        1.11.2 Test scripts GUI tests, some needing larger displays
   1.12 Floating Point Widgets How to input floating point data.
2. Usage Application design.
   2.1 Program structure and operation A simple demo of navigation and use.
   2.2 Callbacks
   2.3 Colors
        2.3.1 Monochrome displays
3. The ssd and display objects
   3.1 SSD class Instantiation in hardware_setup.
   3.2 Display class Instantiation in hardware_setup.
4. Screen class Full screen window.
   4.1 Class methods
   4.2 Constructor
   4.3 Callback methods Methods which run in response to events.
   4.4 Method Optional interface to uasyncio code.
   4.5 Bound variable Control latency caused by garbage collection.
   4.6 Usage Accessing data created in a screen.
5. Window class
   5.1 Constructor
   5.2 Class method
   5.3 Popup windows
6. Widgets Displayable objects.
   6.1 Label widget Single line text display.
        6.1.1 Grid widget A spreadsheet-like array of labels.
   6.2 LED widget Display Boolean values.
   6.3 Checkbox widget Enter Boolean values.
   6.4 Button and CloseButton widgets Pushbutton emulation.
   6.5 ButtonList object Pushbuttons with multiple states.
   6.6 RadioButtons object One-of-N pushbuttons.
   6.7 Listbox widget
   6.8 Dropdown widget Dropdown lists.
   6.9 DialogBox class Pop-up modal dialog boxes.
   6.10 Textbox widget Scrolling text display.
   6.11 Meter widget Display floats on an analog meter, with data driven callbacks.
        6.11.1 Region class
   6.12 Slider and HorizSlider widgets Linear potentiometer float data entry and display
   6.13 Scale widget High precision float entry and display.
   6.14 ScaleLog widget Wide dynamic range float entry and display.
   6.15 Dial widget Display multiple vectors.
   6.16 Knob widget Rotary potentiometer float entry.
   6.17 Adjuster widget Space saving way to enter floats.
   6.18 Menu class
   6.19 BitMap widget Draw bitmaps from files.
   6.20 QRMap widget Draw QR codes created by uQR.
7. Graph plotting Widgets for Cartesian and polar graphs.
   7.1 Concepts
        7.1.1 Graph classes
        7.1.2 Curve classes
        7.1.3 Coordinates
   7.2 Graph classes
        7.2.1 Class CartesianGraph
        7.2.2 Class PolarGraph
   7.3 Curve classes
        7.3.1 Class Curve
        7.3.2 Class PolarCurve
   7.4 Class TSequence Plotting realtime, time sequential data.
8. ESP32 touch pads Replacing buttons with touch pads.
9. Realtime applications Accommodating tasks requiring fast RT performance.
10. ePaper displays Guidance on using ePaper displays.

Appendix 1 Application design Tab order, button layout, encoder interface, use of graphics primitives
Appendix 2 Freezing bytecode Optional way to save RAM.
Appendix 3 Cross compiling Another way to save RAM.

1. Basic concepts

Internally micro-gui uses uasyncio. It presents a conventional callback based interface; knowledge of uasyncio is not required for its use. Display refresh is handled automatically. Widgets are drawn using graphics primitives rather than icons. This makes them efficiently scalable and minimises RAM usage compared to icon-based graphics. It also facilitates the provision of extra visual information. For example the color of all or part of a widget may be changed programmatically, for example to highlight an overrange condition. There is limited support for icons in pushbuttons via icon fonts, also via the BitMap widget.

The following, taken from gui.demos.simple.py, is a complete application. It shows a message and has "Yes" and "No" buttons which trigger a callback.

import hardware_setup  # Create a display instance
from gui.core.ugui import Screen, ssd

from gui.widgets import Label, Button, CloseButton
# from gui.core.writer import Writer  # Monochrome display
from gui.core.writer import CWriter
# Font for CWriter or Writer
import gui.fonts.arial10 as arial10
from gui.core.colors import *


class BaseScreen(Screen):

    def __init__(self):

        def my_callback(button, arg):
            print('Button pressed', arg)

        super().__init__()
        # wri = Writer(ssd, arial10, verbose=False)  # Monochrome display
        wri = CWriter(ssd, arial10, GREEN, BLACK, verbose=False)

        col = 2
        row = 2
        Label(wri, row, col, 'Simple Demo')
        row = 50
        Button(wri, row, col, text='Yes', callback=my_callback, args=('Yes',))
        col += 60
        Button(wri, row, col, text='No', callback=my_callback, args=('No',))
        CloseButton(wri)  # Quit the application

def test():
    print('Simple demo: button presses print to REPL.')
    Screen.change(BaseScreen)  # A class is passed here, not an instance.

test()

Notes:

• Monochrome displays use the Writer class rather than CWriter to render fonts, as per the commented-out code above.
• Hardware is defined by a single small file hardware_setup.py which the user must edit.

1.1 Coordinates

These are defined as row and col values where row==0 and col==0 corresponds to the top left most pixel. Rows increase downwards and columns increase to the right. The graph plotting widget uses normal mathematical conventions within graphs.

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1.2 Screen Window and Widget objects

A Screen is a window which occupies the entire display. A Screen can overlay another, replacing all its contents. When closed, the Screen below is re-displayed.

A Window is a subclass of Screen but is smaller, with size and location attributes. It can overlay part of an underlying Screen and is typically used for dialog boxes. Window objects are modal: a Window can overlay a Screen but cannot overlay another Window.

A Widget is an object capable of displaying data. Some are also capable of data input: such a widget is defined as active. A passive widget can only display data. An active widget can acquire focus. The widget with focus is able to respond to user input. See navigation. Widget objects have dimensions defined as height and width. The space requred by them exceeds these dimensions by two pixels all round. This is because micro-gui displays a surrounding white border to show which object currently has focus. Thus to place a Widget at the extreme top left, row and col values should be 2.

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1.3 Fonts

Python font files are in the gui/fonts directory. The easiest way to conserve RAM is to freeze them which is highly recommended. In doing so the directory structure must be maintained.

To create alternatives, Python fonts may be generated from industry standard font files with font_to_py.py. The -x option for horizontal mapping must be specified. If fixed pitch rendering is required -f is also required. Supplied examples are:

• arial10.py Variable pitch Arial. 10 pixels high.
• arial35.py Arial 35 high.
• arial_50.py Arial 50 high.
• courier20.py Fixed pitch Courier, 20 high.
• font6.py FreeSans 14 high.
• font10.py FreeSans 17 high.
• freesans20.py FreeSans 20 high.

The directory gui/fonts/bitmaps is only required for the bitmap.py demo.

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1.4 Navigation

The GUI requires from 2 to 5 pushbuttons for control. These are:

1. Next Move to the next widget.
2. Select Operate the currently selected widget.
3. Prev Move to the previous widget.
4. Increase Move within the widget (i.e. adjust its value).
5. Decrease Move within the widget.

An alternative is to replace buttons 4 and 5 with a quadrature encoder knob such as this one. That device has a switch which operates when the knob is pressed: this may be wired for the Select button. This provides the most intuitive operation.

Many widgets such as Pushbutton or Checkbox objects require only the Select button to operate: it is possible to design an interface with a subset of micro-gui widgets which requires only the first two buttons. With three buttons all widgets may be used without restriction.

Widgets such as Listbox objects, dropdown lists (Dropdown), and those for floating point data entry can use the Increase and Decrease buttons (or an encoder) to select a data item or to adjust the linear value. If three buttons are provided, the GUI will enter "adjust" mode in response to a double-click of Select. In this mode Prev and Next act to decrease and increase the widget's value. A further double-click restores normal navigation. This is discussed in Floating Point Widgets.

The currently selected Widget is identified by a white border: the focus moves between widgets via Next and Prev. Only active Widget instances (those that can accept input) can receive the focus. Widgets are defined as active or passive in the constructor, and this status cannot be changed. In some cases the state can be specified as a constructor arg, but other widgets have a predefined state. An active widget can be disabled and re-enabled at runtime. A disabled active widget is shown "greyed-out" and cannot accept the focus until re-enabled.

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1.5 Hardware definition

A file hardware_setup.py must exist in the GUI root directory. This defines the connections to the display, the display driver, and pins used for the pushbuttons. Example files may be found in the setup_examples directory. Further examples (without pin definitions) are in this nano-gui directory.

The following is a typical example for a Raspberry Pi Pico driving an ILI9341 display:

from machine import Pin, SPI, freq
import gc

from drivers.ili93xx.ili9341 import ILI9341 as SSD
freq(250_000_000)  # RP2 overclock
# Create and export an SSD instance
pdc = Pin(8, Pin.OUT, value=0)  # Arbitrary pins
prst = Pin(9, Pin.OUT, value=1)
pcs = Pin(10, Pin.OUT, value=1)
spi = SPI(0, baudrate=30_000_000)
gc.collect()  # Precaution before instantiating framebuf
# Instantiate display and assign to ssd. For args see display drivers doc.
ssd = SSD(spi, pcs, pdc, prst, usd=True)
# The following import must occur after ssd is instantiated.
from gui.core.ugui import Display, quiet
# quiet()
# Define control buttons
nxt = Pin(19, Pin.IN, Pin.PULL_UP)  # Move to next control
sel = Pin(16, Pin.IN, Pin.PULL_UP)  # Operate current control
prev = Pin(18, Pin.IN, Pin.PULL_UP)  # Move to previous control
increase = Pin(20, Pin.IN, Pin.PULL_UP)  # Increase control's value
decrease = Pin(17, Pin.IN, Pin.PULL_UP)  # Decrease control's value
# Create a Display instance and assign to display.
display = Display(ssd, nxt, sel, prev, increase, decrease)

Where an encoder replaces the increase and decrease buttons, only the final line needs to be changed to provide an extra arg:

display = Display(ssd, nxt, sel, prev, increase, decrease, 4)

The final arg specifies the sensitivity of the attached encoder, the higher the value the more the knob has to be turned for a desired effect. A value of 1 provides the highest sensitivity, being the native rate of the encoder. Many encoders have mechanical detents: a value of 4 matches the click rate of most devices.

The commented-out quiet() line provides a means of suppressing diagnostic messages.

Instantiation of SSD and Display classes is detailed in section 3.

Display drivers are documented here.

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1.6 Quick hardware check

The following may be pasted at the REPL to verify correct connection to the display. It also confirms that hardware_setup.py is specifying a suitable display driver.

from hardware_setup import ssd  # Create a display instance
from gui.core.colors import *
ssd.fill(0)
ssd.line(0, 0, ssd.width - 1, ssd.height - 1, GREEN)  # Green diagonal corner-to-corner
ssd.rect(0, 0, 15, 15, RED)  # Red square at top left
ssd.rect(ssd.width -15, ssd.height -15, 15, 15, BLUE)  # Blue square at bottom right
ssd.show()

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1.7 Installation

The easy way to start is to use mpremote which allows a directory on your PC to be mounted on the host. In this way the filesystem on the host is left unchanged. This is at some cost in loading speed, especially on ESP32. If adopting this approach, you will need to ensure the hardware_setup.py file on the PC matches your hardware. Install mpremote with

$ pip3 install mpremote

Clone the repo to your PC with

$ git clone https://github.com/peterhinch/micropython-micro-gui
$ cd micropython-micro-gui

Edit hardware_setup.py then run:

$ mpremote mount .

This should provide a REPL. Run the minimal demo:

>>> import gui.demos.simple

If installing to the device's filesystem it is necessary to maintain the directory structure. The drivers and gui directories (with subdirectories and contents) should be copied, along with hardware_setup.py. Filesystem space may be conserved by copying only the display driver in use. Unused widgets, fonts and demos can also be trimmed, but the directory structure must be kept. Below is an example of a minimal installation to run the simple.py demo.

There is scope for speeding loading and saving RAM by using frozen bytecode. The entire gui tree may be frozen but the directory structure must be maintained. For reasons that are unclear freezing display drivers does not work. For fexibility, consider keeping hardware_setup.py in the filesystem. See Appendix 2 Freezing bytecode.

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1.8 Performance and hardware notes

RAM usage

Running the linked_sliders demo, the code uses about 23,000 bytes with frozen bytecode and 55,000 bytes without. To this must be added the size of the frame buffer. This can readily be calculated. For example in the case of the ILI9341 (a 240x320 pixel unit whose driver uses 4-bit color) the buffer size is
240x320/2 = 38,400 bytes.

A Pico shows ~182000 bytes free with no code running. With linked_sliders running on an ILI9341 display, it shows 120,896 bytes free with frozen bytecode and 88,640 bytes free without.

With multi-pixel displays the size of the frame buffer can prevent the GUI from compiling. If frozen bytecode is impractical, consider cross-compiling. See Appendix 3 Cross compiling.

Speed

The consequence of inadequate speed is that brief button presses can be missed. This is because display update blocks for tens of milliseconds, during which time the pushbuttons are not polled. This can be an issue in displays with a large number of pixels, multi-byte colors and/or slow SPI clock rates. In high resolution cases the device driver has specfic uasyncio support whereby the driver yields to the scheduler a few times during the refresh.Currently this exists on ILI9486, ILI9341 and ST7789 (e.g. TTGO T-Display). By my calculations and measurements this should be unnecessary on other drivers, but please report any tendency to miss button presses and I will investigate.

This may be mitigated by two approaches:

1. Clocking the SPI bus as fast as possible. This is discussed in the drivers doc.
2. Clocking the host fast (machine.freq).

Platform notes

On ESP32 (including the TTGO T-Display) note that pins 36-39 are input-only and do not have pullup support: if these are used for pushbutton input, physical pullups to 3.3V should be used. See ref.

On a Pyboard 1.1 with 320x240 ili9341 display it was necessary to use frozen bytecode: in this configuration running the various.py demo there was 29K of free RAM. Note that, at 37.5KiB, this display is the worst-case in terms of RAM usage. A smaller display or a Pyboard D would offer more headroom. Frozen bytecode was also necessary on an RP2 running an ILI9486: a 480x320 display requires a 76,800 byte frame buffer.

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1.9 Firmware and dependencies

Firmware should be V1.17 or later. The source tree includes all dependencies. These are listed to enable users to check for newer versions or to read docs:

• writer.py Provides text rendering of Python font files.
• SSD1306 driver. A copy of the official driver for OLED displays using the SSD1306 chip is provided. The link is to the official file.
• Synchronisation primitives. The link is to my uasyncio support repo.
• PCD8544/Nokia 5110. Displays based on the Nokia 5110 (PCD8544 chip) require this driver. It is not provided in this repo. The link is to its source.

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1.10 Supported hosts and displays

Development was done using a Raspberry Pi Pico connected to a cheap ILI9341 320x240 display. I have also tested a TTGO T-Display (an ESP32 host) and a Pyboard. Code is written with portability as an aim, but MicroPython configs vary between platforms and I can't guarantee that every widget will work on every platform. For example, some use the cmath module which may be absent on some builds.

Supported displays are as per the nano-gui list. In general ePaper and Sharp displays are unlikely to yield good results because of slow and visually intrusive refreshing. However there is an exception: the Waveshare pico_epaper_42. See 10. ePaper displays.

Display drivers are documented here.

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1.11 Files

Display drivers may be found in the drivers directory. These are copies of those in nano-gui, included for convenience. Note the file drivers/boolpalette.py, required by all color drivers.

The system is organised as a Python package with the root being gui. Core files in gui/core are:

• colors.py Constants including colors and shapes.
• ugui.py The main GUI code.
• writer.py Supports the Writer and CWriter classes.

The gui/primitives directory contains the following files:

• pushbutton.py Interface to physical pushbuttons and ESP32 touch pads.
• delay_ms.py A software triggerable timer.
• encoder.py Driver for a quadrature encoder. This offers an alternative interface - see Appendix 1.

The gui/demos directory contains a variety of demos and tests described below.

1.11.1 Demos

Demos are run by issuing (for example):

>>> import gui.demos.simple

If shut down cleanly with the "close" button a demo can be re-run with (e.g.):

gui.demos.simple.test()

Before running a different demo the host should be reset (ctrl-d) to clear RAM.

These will run on screens of 128x128 pixels or above. The initial ones are minimal and aim to demonstrate a single technique.

• simple.py Minimal demo discussed below. Button presses print to REPL.
• checkbox.py A Checkbox controlling an LED.
• slider.py A Slider whose color varies with its value.
• slider_label.py A Slider updating a Label. Good for trying precision mode.
• linked_sliders.py One Slider updating two others, and a coding "wrinkle" required for doing this.
• dropdown.py A dropdown list (with scrolling) updates a Label.
• listbox.py A listbox with scrolling.
• dialog.py DialogBox demo. Illustrates the screen change mechanism.
• screen_change.py A Pushbutton causing a screen change using a re-usable "forward" button.
• primitives.py Use of graphics primitives.
• aclock.py An analog clock using the Dial vector display. Also shows screen layout using widget metrics. Has a simple uasyncio task.
• tbox.py Text boxes and user-controlled scrolling.
• tstat.py A demo of the Meter class with data sensitive regions.
• menu.py A multi-level menu.
• adjuster.py Simple demo of the Adjuster control.
• adjust_vec.py A pair of Adjusters vary a vector.
• bitmap.py Demo of the BitMap widget showing a changing image.
• qrcode.py Display a QR code. Requires the uQR module.
• calendar.py Demo of grid widget.
• epaper.py Warts-and-all demo for an ePaper display. Currently the only supported display is the Waveshare pico_epaper_42 with Pico or other host.

1.11.2 Test scripts

These more complex demos are run in the same way by issuing (for example):

>>> import gui.demos.active

Some of these require larger screens. Required sizes are specified as (height x width).

• active.py Demonstrates active controls providing floating point input (240x320).
• plot.py Graph plotting (128x200).
• screens.py Listbox, dropdown and dialog boxes (128x240).
• various.py Assorted widgets including the different types of pushbutton (240x320).
• vtest.py Clock and compass styles of vector display (240x320).
• calendar.py Demo of grid control (240x320 - but could be reduced).

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1.12 Floating Point Widgets

Some applications need to adjust a data value with an extremely large dynamic range. This is the ratio of the data value's total range to the smallest adjustment that can be made. The mechanism currently implemented enables a precision of 0.05%.

Floating point widgets respond to a brief press of the increase or decrease buttons by adjusting the value by a small amount. A continued press causes the value to be repeatedly adjusted, with the amount of the adjustment increasing with time. This enables the entire range of the control to be accessed quickly, while allowing small changes of 0.5%. This works well. In many cases the level of precision will suffice. An encoder provides similar performance.

Fine adjustments may be achieved by pressing the select button for at least one second. The GUI will respond by changing the border color from white (i.e. has focus) to yellow. In this mode a brief press of increase or decrease or small movement of an encoder will have a reduced effect (0.05%). Fine mode may be cancelled by pressing select or by moving the focus to another control. This also works in three-button mode, with Next and Prev performing the adjustments.

In the case of slider and knob controls the precision of fine mode exceeds that of the visual appearance of the widget: fine changes can be too small to see. Options are to use the Scale widget or to have a linked Label showing the widget's exact value.

The callback runs whenever the widget's value changes. This causes the callback to run repeatedly while the user adjusts the widget. This is required if there is a linked Label to update.

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2. Usage

2.1 Program structure and operation

The following is a minimal script (found in gui.demos.simple.py) which will run on a minimal system with a small display and two pushbuttons. Commented out code shows changes for monochrome displays.

The demo provides two Button widgets with "Yes" and "No" legends. It may be run by issuing at the REPL:

>>> import gui.demos.simple

Note that the import of hardware_setup.py is the first line of code. This is because the frame buffer is created here, with a need for a substantial block of contiguous RAM.

import hardware_setup  # Instantiate display, setup color LUT (if present)
from gui.core.ugui import Screen, ssd

from gui.widgets import Label, Button, CloseButton
# from gui.core.writer import Writer  # Monochrome display
from gui.core.writer import CWriter

# Font for CWriter
import gui.fonts.arial10 as arial10
from gui.core.colors import *


class BaseScreen(Screen):

    def __init__(self):

        def my_callback(button, arg):
            print('Button pressed', arg)

        super().__init__()
        # wri = Writer(ssd, arial10, verbose=False)
        wri = CWriter(ssd, arial10, GREEN, BLACK, verbose=False)

        col = 2
        row = 2
        Label(wri, row, col, 'Simple Demo')
        row = 20
        Button(wri, row, col, text='Yes', callback=my_callback, args=('Yes',))
        col += 60
        Button(wri, row, col, text='No', callback=my_callback, args=('No',))
        CloseButton(wri)  # Quit the application

def test():
    print('Testing micro-gui...')
    Screen.change(BaseScreen)

test()

Note how the Next pushbutton moves the focus between the two buttons and the "X" close button. The focus does not move to the "Simple Demo" widget because it is not active: a Label cannot accept user input. Pushing the Select pushbutton while the focus is on a Pushbutton causes the callback to run.

Applications start by performing Screen.change() to a user-defined Screen object. This must be subclassed from the GUI's Screen class. Note that Screen.change accepts a class name, not a class instance.

The user defined BaseScreen class constructor instantiates all widgets to be displayed and typically associates them with callback functions - which may be bound methods. Screens typically have a CloseButton widget. This is a special Pushbutton subclass which displays as an "X" at the top right corner of the physical display and closes the current screen, showing the one below. If used on the bottom level Screen (as above) it closes the application.

The CWriter instance wri associates a widget with a font. Constructors for all widgets have three mandatory positional args. These are a CWriter instance followed by row and col. These args are followed by a number of optional keyword args. These have (hopefully) sensible defaults enabling you to get started easily. Monochrome displays use the simpler Writer class.

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2.2 Callbacks

The interface is event driven. Widgets may have optional callbacks which will be executed when a given event occurs. Events occur when a widget's properties are changed programmatically, and also (in the case of active widgets) in response to user input.

A callback function receives positional arguments. The first is a reference to the object raising the callback. Subsequent arguments are user defined, and are specified as a tuple or list of items. Callbacks and their argument lists are optional: a default null function and empty tuple are provided. Callbacks may optionally be written as bound methods. This facilitates communication between widgets.

When writing callbacks take care to ensure that the correct number of arguments are passed, bearing in mind the first arg described above. An incorrect argument count results in puzzling tracebacks which appear to implicate the GUI code. This is because it is the GUI which actually executes the callbacks.

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2.3 Colors

The file gui/core/colors.py defines a set of color constants which may be used with any display driver. This section describes how to change these or to create additional colors. Most of the color display drivers define colors as 8-bit or larger values. For the larger displays 4-bit drivers are provided with the aim of conserving RAM.

In the 4-bit case colors are assigned to a lookup table (LUT) with 16 entries. The frame buffer stores 4-bit color values, which are converted to the correct color depth for the hardware when the display is refreshed. Of the 16 possible colors 13 are assigned in gui/core/colors.py, leaving color numbers 12, 13 and 14 free.

The following code is portable between displays and creates a user defined color PALE_YELLOW.

from gui.core.colors import *  # Imports the create_color function
PALE_YELLOW = create_color(12, 150, 150, 0)  # index, r, g, b

If a 4-bit driver is in use, the color rgb(150, 150, 0) will be assigned to "spare" color number 12. Any color number in range 0 <= n <= 15 may be used, implying that predefined colors may be reassigned. It is recommended that BLACK (0) and WHITE (15) are not changed. If an 8-bit or larger driver is in use, the color number is ignored and there is no practical restriction on the number of colors that may be created.

In the above example, regardless of the display driver, the PALE_YELLOW variable may be used to refer to the color. An example of custom color definition may be found in this nano-gui demo.

There are five default colors which are defined by a color_map list. These may be reassigned in user code. For example the following will cause the border of any control with the focus to be red:

from colors import *
color_map[FOCUS] = RED

The color_map index constants and default colors (defined in colors.py) are:

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2.3.1 Monochrome displays

Most widgets work on monochrome displays if color settings are left at default values. If a color is specified, drivers in this repo will convert it to black or white depending on its level of saturation. A low level will produce the background color, a high level the foreground.

At the bit level 1 represents the foreground. This is white on an emitting display such as an OLED. On a Sharp display it indicates reflection.

There is an issue regarding ePaper displays discussed here. The driver for the Waveshare pico_epaper_42 renders colored objects as black on white.

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3. The ssd and display objects

The following code, issued as the first executable lines of an application, initialises the display.

import hardware_setup  # Create a display instance
from gui.core.ugui import Screen, ssd, display  # display symbol is seldom needed

The hardware_setup file creates singleton instances of SSD and Display classes. These instances are made available via ugui. Normal GUI applications only need to import ssd. This refererence to the display driver is used to initialise Writer objects. Bound variables ssd.height and ssd.width may be read to determine the dimensions of the display hardware.

The display object is only needed in applications which use graphics primitives to write directly to the screen. See Appendix 1 Application design.

3.1 SSD class

This is instantiated in hardware_setup.py. The specific class must match the display hardware in use. Display drivers are documented here.

3.2 Display class

This is instantiated in hardware_setup.py. It registers the SSD instance along with the Pin instances used for input; also whether an encoder is used. Pins are arbitrary, but should be defined as inputs with pullups. Pushbuttons are connected between Gnd and the relevant pin.

The constructor takes the following positional args:

1. objssd The SSD instance. A reference to the display driver.
2. nxt A Pin instance for the next button.
3. sel A Pin instance for the select button.
4. prev=None A Pin instance for the previous button (if used).
5. incr=None A Pin instance for the increase button (if used).
6. decr=None A Pin instance for the decrease button (if used).
7. encoder=False If an encoder is used, an integer must be passed.
8. touch=False Supply an integer to use ESP32 TouchPad instances in place of all physical pushbuttons. See ESP32 touch pads.

Class variables:

• verbose=True Causes a message to be printed indicating whether an encoder was specified.

Encoder usage

If an encoder is used, it should be connected to the pins assigned to increase and decrease. If the direction of movement is wrong, these pins should be transposed (physically or in code).

To specify to the GUI that an encoder is in use an integer should be passed to the Display constructor encoder arg. Its value represents the division ratio. A value of 1 defines the native rate of the encoder; if the native rate is 32 pulses per revolution, a value of 4 would yield a virtual device with 8 pulses per rev. A value of 4 matches most encoders with mechanical detents.

If an encoder is used but the encoder arg is False, response to the encoder will be erratic.

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4. Screen class

The Screen class presents a full-screen canvas onto which displayable objects are rendered. Before instantiating widgets a Screen instance must be created. This will be current until another is instantiated. When a widget is instantiated it is associated with the current screen.

All applications require the creation of at least one user screen. This is done by subclassing the Screen class. Widgets are instantiated in the Screen constructor. Widgets may be assigned to bound variable: this facilitates communication between them.

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4.1 Class methods

In normal use the following methods only are required:

• change(cls, cls_new_screen, *, forward=True, args=[], kwargs={}) Change screen, refreshing the display. Mandatory positional argument: the new screen class name. This must be a class subclassed from Screen. The class will be instantiated and displayed. Optional keyword arguments args, kwargs enable passing positional and keyword arguments to the constructor of the new, user defined, screen.
• back(cls) Restore previous screen.

These are uncommon:

• shutdown(cls) Clear the screen and shut down the GUI. Normally done by a CloseButton instance.
• show(cls, force). This causes the screen to be redrawn. If force is False unchanged widgets are not refreshed. If True, all visible widgets are re-drawn. Explicit calls to this should never be needed.

See demos/plot.py for an example of multi-screen design, or screen_change.py for a minimal example demostrating the coding technique.

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4.2 Constructor

This takes no arguments.

4.3 Callback methods

These are null functions which may be redefined in user subclasses.

• on_open(self) Called when a screen is instantiated but prior to display.
• after_open(self) Called after a screen has been displayed.
• on_hide(self) Called when a screen ceases to be current.

See demos/plot.py for examples of usage of after_open.

4.4 Method

• reg_task(self, task, on_change=False) The first arg may be a Task instance or a coroutine.

This is a convenience method which provides for the automatic cancellation of tasks. If a screen runs independent tasks it can opt to register these. If the screen is overlaid by another, tasks registered with on_change True are cancelled. If the screen is closed, all tasks registered to it are cancelled regardless of the state of on_change. On shudown, any tasks registered to the base screen are cancelled.

For finer control, applications can ignore this method and handle cancellation explicitly in code.

4.5 Class variable

• do_gc = True By default a coroutine is launched to periodically perform garbage collection (GC). On most platforms this reduces latency by doing GC before too much garbage has accumulated. However on platforms with SPIRAM GC can take hundreds of ms, causing unacceptable latency. If do_gc is False the application can perform GC at times when fast response to user actions is not required. If turned off, the GC task cannot be re-started.

4.6 Usage

The Screen.change() classmethod returns immediately. This has implications where the new, top screen sets up data for use by the underlying screen. One approach is for the top screen to populate class variables. These can be acccessed by the bottom screen's after_open method which will run after the top screen has terminated.

If a Screen throws an exception when instantiated, check that its constructor calls super().__init__().

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5. Window class

This is a Screen subclass providing for modal windows. As such it has positional and dimension information. Usage consists of writing a user class subclassed from Window. Example code is in demos/screens.py. Code in a window must not attempt to open another Window or Screen. Doing so will raise a ValueError. Modal behaviour means that the only valid screen change is a return to the calling screen.

5.1 Constructor

This takes the following positional args:

• row
• col
• height
• width

Followed by keyword-only args

• draw_border=True
• bgcolor=None Background color, default black.
• fgcolor=None Foreground color, default white.
• writer=None See Popups below.

5.2 Class method

• value(cls, val=None) The val arg can be any Python type. It allows widgets on a Window to store information in a way which can be accessed from the calling screen. This typically occurs after the window has closed and no longer exists as an instance.

Another approach, demonstrated in demos/screens.py, is to pass one or more callbacks to the user window constructor args. These may be called by widgets to send data to the calling screen. Note that widgets on the screen below will not be updated until the window has closed.

5.3 Popup windows

In general Screen and Window instances need at least one active widget. There is a special case of a popup window which typically displays status data, possibly with a progress meter. A popup has no user controls and is closed by user code. A popup is created by passing a Writer (or CWriter) to the constructor and is closed by issuing the close() static method.

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6. Widgets

6.1 Label widget

from gui.widgets import Label  # File: label.py

Various styles of Label.

The purpose of a Label instance is to display text at a specific screen location.

Text can be static or dynamic. In the case of dynamic text the background is cleared to ensure that short strings cleanly replace longer ones.

Labels can be displayed with an optional single pixel border.

Colors are handled flexibly. By default the colors used are those of the Writer instance, however they can be changed dynamically; this might be used to warn of overrange or underrange values. The color15.py demo illustrates this.

Constructor args:

1. writer The Writer instance (font and screen) to use.
2. row Location on screen.
3. col
4. text If a string is passed it is displayed: typically used for static text. If an integer is passed it is interpreted as the maximum text length in pixels; typically obtained from writer.stringlen('-99.99'). Nothing is dsplayed until .value() is called. Intended for dynamic text fields.
5. invert=False Display in inverted or normal style.
6. fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
7. bgcolor=BLACK Background color of object. If None the Writer background default is used.
8. bdcolor=False Color of border. If False no border will be drawn. If None the fgcolor will be used, otherwise a color may be passed. If a color is available, a border line will be drawn around the control.
9. justify=Label.LEFT Options are Label.RIGHT and Label.CENTRE (note British spelling). Justification can only occur if there is sufficient space in the Label i.e. where an integer is supplied for the text arg.

The constructor displays the string at the required location.

Method:
value Redraws the label. This takes the following args:

• text=None The text to display. If None displays last value.
• invert=False If true, show inverse text.
• fgcolor=None Foreground color: if None the Writer default is used.
• bgcolor=None Background color, as per foreground.
• bdcolor=None Border color. As per above except that if False is passed, no border is displayed. This clears a previously drawn border.
  Returns the current text string.
• justify=None By default justify using the constructor default. Override with Label.LEFT, Label.RIGHT or Label.CENTRE.

If the value method is called with a text string too long for the Label the text will be clipped to fit the width. In this case value() will return the truncated text.

If constructing a label would cause it to extend beyond the screen boundary a warning is printed at the console. The label may appear at an unexpected place. The following is a complete "Hello world" script.

from hardware_setup import ssd  # Create a display instance
from gui.core.ugui import Screen
from gui.core.writer import CWriter
from gui.core.colors import *

from gui.widgets import Label, CloseButton
import gui.fonts.freesans20 as freesans20


class BaseScreen(Screen):

    def __init__(self):
        super().__init__()
        wri = CWriter(ssd, freesans20, GREEN, BLACK, verbose=False)
        Label(wri, 2, 2, 'Hello world!')
        CloseButton(wri)

Screen.change(BaseScreen)

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6.1.1 Grid widget

from gui.widgets import Grid  # Files: grid.py, parse2d.py

This is a rectangular array of Label instances: as such it is a passive widget. Rows are of a fixed height equal to the font height + 4 (i.e. the label height). Column widths are specified in pixels with the column width being the specified width +4 to allow for borders. The dimensions of the widget including borders are thus:
height = no. of rows * (font height + 4)
width = sum(column width + 4)
Cells may be addressed as a 1 or 2-dimensional array.

Constructor args:

1. writer The Writer instance (font and screen) to use.
2. row Location of grid on screen.
3. col
4. lwidth If an integer N is passed all labels will have width of N pixels. A list or tuple of integers will define the widths of successive columns. If the list has fewer entries than there are columns, the last entry will define the width of those columns. Thus [20, 30] will produce a grid with column 0 being 20 pixels and all subsequent columns being 30.
5. nrows Number of rows.
6. ncols Number of columns.
7. invert=False Display in inverted or normal style.
8. fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
9. bgcolor=BLACK Background color of cells. If None the Writer background default is used.
10. bdcolor=None Color of border of the widget and its internal grid. If False no border or grid will be drawn. If None the fgcolor will be used, otherwise a color may be passed.
11. justify=Label.LEFT Options are Label.RIGHT and Label.CENTRE (note British spelling). Justification can only occur if there is sufficient space in the Label as defined by lwidth.

Method:

• __getitem__ Return a list containing one or more Label instances.
• __setitem__ Assign a value to one or more labels. If multiple labels are specified and a single text value is passed, all labels will receive that value. If an iterator is passed, consecutive labels will receive values from the iterator. If the iterator runs out of data, the last value will be repeated.

Addressing:
The Label instances may be addressed as a 1D array as follows

grid[20] = str(42)
grid[20:25] = iter([str(n) for n in range(20, 25)])

or as a 2D array:

grid[2, 5] = "A"  # Row == 2, col == 5
grid[0:7, 3] = "b"  # Populate col 3 of rows 0..6
grid[1:3, 1:3] = (str(n) for n in range(25))  # Produces
# 0 1
# 2 3

Columns are populated from left to right, rows from top to bottom. Unused iterator values are ignored. If an iterator runs out of data the last value is repeated, thus

grid[1:3, 1:3] = (str(n) for n in range(2))  # Produces
# 0 1
# 1 1

Example uses:

colwidth = (20, 30)  # Col 0 width is 20, subsequent columns 30
self.grid = Grid(wri, row, col, colwidth, rows, cols, justify=Label.CENTRE)
self.grid[20] = ""  # Clear cell 20 by setting its value to ""
self.grid[2, 5] = str(42)  # 2D array syntax
grid[1:6, 0] = iter("ABCDE")  # Label row and col headings
grid[0, 1:cols] = (str(x + 1) for x in range(cols))
d = {}  # For indiviual control of cell appearance
d["fgcolor"] = RED
d["text"] = str(99)
self.grid[3, 7] = d  # Specify color as well as text
del d["fgcolor"]  # Revert to default
d["invert"] = True
self.grid[17] = d

See the example calendar.py.

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6.2 LED widget

from gui.widgets import LED  # File: led.py

This is a virtual LED whose color may be altered dynamically. An LED may be defined with a color and turned on or off by setting .value to a boolean. For more flexibility the .color method may be use to set it to any color.

Constructor mandatory positional args:

1. writer The Writer instance (defines font) to use.
2. row Location on screen.
3. col

Keyword only args:

• height=30 Height of LED.
• fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
• bgcolor=None Background color of object. If None the Writer background default is used.
• bdcolor=False Color of border. If False no border will be drawn. If a color is provided, a border line will be drawn around the control. shown in the foreground color. If a color is passed, it is used.
• color=RED Color when illuminated (i.e. if value is True.

Methods:

1. value arg val=None If True is passed, lights the LED in its current color. False extinguishes it. None has no effect. Returns current value.
2. color arg c=None Change the LED color to c. If c is None the LED is turned off (rendered in the background color).

Note that __call__ is a synonym for value. An LED instance can be controlled with led(True) or led(False).

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6.3 Checkbox widget

from gui.widgets import Checkbox  # File: checkbox.py

This provides for Boolean data entry and display. In the True state the control can show an 'X' or a filled block of any color depending on the fillcolor constructor arg.

Constructor mandatory positional args:

1. writer The Writer instance (defines font) to use.
2. row Location on screen.
3. col

Optional keyword only arguments:

• height=30 Dimension of the square bounding box. Default 30 pixels.
• fillcolor=None Fill color of checkbox when True. If None an 'X' will be drawn.
• fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
• bgcolor=None Background color of object. If None the Writer background default is used.
• bdcolor=False Color of border. If False no border will be drawn. If a color is provided, a border line will be drawn around the control.
• callback=dolittle Callback function which will run when the value changes. The default is a null function.
• args=[] A list/tuple of arguments for above callback.
• value=False Initial value.
• active=True By default user input is accepted.

Methods:

• greyed_out Optional Boolean argument val=None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
• value Optional Boolean argument val. If the provided value does not correspond to the control's current value, updates it; the checkbox is re-drawn and the callback executed. Always returns the control's value.

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6.4 Button and CloseButton widgets

from gui.core.colors import *  # Colors and shapes
from gui.widgets import Button  # File: buttons.py

Using an icon font:

In these images Button "a" and the "Forward" button have the focus. Pressing the physical select button will press the virtual Button.

This emulates a pushbutton, with a callback being executed each time the button is pressed. Physically this consists of pressing the select button when the Button instance has focus. Buttons may be any one of three shapes: CIRCLE, RECTANGLE or CLIPPED_RECT.

Constructor mandatory positional args:

1. writer The Writer instance (defines font) to use.
2. row Location on screen.
3. col

Optional keyword only arguments:

• shape=RECTANGLE Must be CIRCLE, RECTANGLE or CLIPPED_RECT.
• height=20 Height of button or diameter in CIRCLE case.
• width=50 Width of button. If text is supplied and width is too low to accommodate the text, it will be increased to enable the text to fit. In CIRCLE case any passed value is ignored.
• fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
• bgcolor=None Background color of object. If None the Writer background default is used.
• bdcolor=False Color of border. If False no border will be drawn. If a color is provided, a border line will be drawn around the control.
• textcolor=None Text color. Defaults to fgcolor.
• litcolor=None If provided the button will display this color for one second after being pressed.
• text='' Shown in centre of button. It is possible to show simple icons, for example media playback symbols.
• callback=dolittle Callback function which runs when button is pressed.
• args=() A list/tuple of arguments for the above callback.

Method:

• greyed_out Optional Boolean argument val=None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.

Class variable:

• lit_time=1 Period in seconds the litcolor is displayed.

CloseButton

This example has focus, as shown by white border.

This Button subclass is a special case of a Button. Its constructor takes a single arg, being a Writer instance. It produces a red "X" button at the top right hand corner of the current Screen. Operating it causes the screen to close, with the screen below being revealed. On the bottom level screen, a CloseButton will shut down the application.

Constructor mandatory positional arg:

• writer

Optional keyword only arguments:

• width=0 By default dimensions are calculated from font size. The button is is square. Optionally width may be specified.
• callback=dolittle Optional callback, not normally required.
• args=() Args for above.
• bgcolor=RED

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6.5 ButtonList object

from gui.core.colors import *  # Colors and shapes
from gui.widgets import Button, ButtonList  # File: buttons.py

A ButtonList groups a number of buttons together to implement a button which changes state each time it is pressed. For example it might toggle between a green Start button and a red Stop button. The buttons are defined and added in turn to the ButtonList object. Typically they will be the same size, shape and location but will differ in color and/or text. At any time just one of the buttons will be visible, initially the first to be added to the object.

Buttons in a ButtonList should not have callbacks. The ButtonList has its own user supplied callback which runs each time the object is pressed. However each button can have its own list of args. Callback arguments comprise the currently visible button followed by its arguments.

Constructor argument:

• callback=dolittle The callback function. Default does nothing.

Methods:

• add_button Adds a button to the ButtonList. Arguments: as per the Button constructor. Returns the button object.
• greyed_out Optional Boolean argument val=None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
• value Optional args button=None, new_cb=False. The button arg, if provided, should be a button in the set. If supplied and the button is not active the currency changes to the supplied button, which is displayed. By default the callback of the previous button is run, otherwise the callback of the newly displayed button.

Always returns the active button.

Counter intuitively, running the callback of the previous button is normal behaviour. Consider a ButtonList consisting of ON and OFF buttons. If ON is visible this implies that the machine under control is off. Pressing select causes the ON callback to run, starting the machine. The new button displayed now reads OFF.

Typical usage is as follows:

def callback(button, arg):
    print(arg)

table = [
     {'fgcolor' : GREEN, 'shape' : CLIPPED_RECT, 'text' : 'Start', 'args' : ['Live']},
     {'fgcolor' : RED, 'shape' : CLIPPED_RECT, 'text' : 'Stop', 'args' : ['Die']},
]
bl = ButtonList(callback)
for t in table:  # Buttons overlay each other at same location
    bl.add_button(wri, 10, 10, textcolor = BLACK, **t)

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6.6 RadioButtons object

from gui.core.colors import *  # Colors and shapes
from gui.widgets import Button, RadioButtons  # File: buttons.py

This object groups a set of buttons at different locations. When a button is pressed, it becomes highlighted and remains so until another button in the set is pressed. A callback runs each time the current button is changed.

Constructor positional arguments:

• highlight Color to use for the highlighted button. Mandatory.
• callback Callback when a new button is pressed. Default does nothing.
• selected Index of initial button to be highlighted. Default 0.

Methods:

• add_button Adds a button. Arguments: as per the Button constructor. Returns the Button instance.
• greyed_out Optional Boolean argument val=None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
• value Optional argument: a button in the set. If supplied, and the button is not currently active, the supplied button receives the focus and its callback is run. Always returns the currently active button.

Typical usage:

def callback(button, arg):
    print(arg)

table = [
    {'text' : '1', 'args' : ['1']},
    {'text' : '2', 'args' : ['2']},
    {'text' : '3', 'args' : ['3']},
    {'text' : '4', 'args' : ['4']},
]
col = 0
rb = RadioButtons(BLUE, callback) # color of selected button
for t in table:
    rb.add_button(wri, 10, col, textcolor = WHITE,
                  fgcolor = LIGHTBLUE, height = 40, **t)
    col += 60 # Horizontal row of buttons

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6.7 Listbox widget

from gui.widgets import Listbox  # File: listbox.py

A listbox with the second item highlighted. Pressing the physical select button will cause the callback to run.

A Listbox is an active widget. By default its height is determined by the number of entries in it and the font in use. It may be reduced by specifying dlines in which case scrolling will occur. When the widget has focus the currently selected element may be changed using increase and decrease buttons or by turning the encoder. On pressing select a callback runs.

Constructor mandatory positional args:

1. writer The Writer instance (defines font) to use.
2. row Location on screen.
3. col

Mandatory keyword only argument:

• elements A list or tuple of strings to display. Must have at least one entry. An alternative format is described below which enables each item in the list to have a separate callback.

Optional keyword only arguments:

• dlines=None By default the height of the control is determined by the number of elements. If an integer < number of elements is passed the list will show that number of lines; its height will correspond. Scrolling will occur to ensure that the current element is always visible. To indicate when scrolling is possible, one or two vertical bars will appear to the right of the list.
• width=None Control width in pixels. By default this is calculated to accommodate all elements. If a width is specified, and some elements are too long to fit, they will be clipped. This is a visual effect only and does not affect the value of that element.
• value=0 Index of currently selected list item. If necessary the list will scroll to ensure the item is visible.
• fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
• bgcolor=None Background color of object. If None the Writer background default is used.
• bdcolor=False Color of border. If False no border will be drawn. If a color is provided, a border line will be drawn around the control.
• fontcolor=None Text color. Defaults to system text color.
• select_color=DARKBLUE Background color for selected item in list.
• callback=dolittle Callback function which runs when select is pressed.
• args=[] A list/tuple of arguments for above callback.
• also=0 Options are Listbox.ON_MOVE or Listbox.ON_LEAVE. By default the callback runs only when the select button is pressed. The ON_LEAVE value causes it also to run when the focus moves from the control if the currently selected element has changed. The ON_MOVE arg causes the callback to run every time the highlighted element is changed.

Methods:

• greyed_out Optional Boolean argument val=None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
• value Argument val=None. If a provided argument is a valid index for the list, that entry becomes current and the callback is executed. Always returns the index of the currently active entry.
• textvalue Argument text=None. If a string argument is provided and is in the control's list, that item becomes current. Normally returns the current string. If a provided arg did not match any list item, the control's state is not changed and None is returned.

The callback's first argument is the listbox instance followed by any args specified to the constructor. The currently selected item may be retrieved by means of the instance's value or textvalue methods.

Alternative approach

By default the Listbox runs a common callback regardless of the item chosen. This can be changed by specifying elements such that each element comprises a 3-list or 3-tuple with the following contents:

1. String to display.
2. Callback.
3. Tuple of args (may be ()).

In this case constructor args callback and args must not be supplied. Args received by the callback functions comprise the Listbox instance followed by any supplied args. The following is a complete example (minus initial import statements).

class BaseScreen(Screen):
    def __init__(self):
        def cb(lb, s):
            print('Callback', s)

        def cb_radon(lb, s):
            print('Radioactive', s)

        super().__init__()
        wri = CWriter(ssd, freesans20, GREEN, BLACK, verbose=False)
        els = (('Hydrogen', cb, ('H2',)),
               ('Helium', cb, ('He',)),
               ('Neon', cb, ('Ne',)),
               ('Xenon', cb, ('Xe',)),
               ('Radon', cb_radon, ('Ra',)))
        Listbox(wri, 2, 2, elements = els, bdcolor=RED)
        CloseButton(wri)

Screen.change(BaseScreen)

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6.8 Dropdown widget

from gui.widgets import Dropdown  # File: dropdown.py

Closed dropdown list.

Open dropdown list. When closed, hidden items below are refreshed.

A dropdown list. The list, when active, is drawn over the control. The height of the control is determined by the height of the font in use. By default the height of the list is determined by the number of entries in it and the font in use. It may be reduced by specifying dlines in which case scrolling will occur. The dropdown should be placed high enough on the screen to ensure that the list can be displayed.

Constructor mandatory positional args:

1. writer The Writer instance (defines font) to use.
2. row Location on screen.
3. col

Mandatory keyword only argument:

• elements A list or tuple of strings to display. Must have at least one entry. See below for an alternative way to use the Dropdown which enables each item on the dropdown list to have a separate callback.

Optional keyword only arguments:

• dlines=None By default the height of the dropdown list is determined by the number of elements. If an integer < number of elements is passed the list will show that number of lines; its height will correspond. Scrolling will occur to ensure that the current element is always visible. To indicate when scrolling is possible, one or two vertical bars will appear to the right of the list.
• width=None Control width in pixels. By default this is calculated to accommodate all elements.
• value=0 Index of currently selected list item.
• fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
• bgcolor=None Background color of object. If None the Writer background default is used.
• bdcolor=False Color of border. If False no border will be drawn. If a color is provided, a border line will be drawn around the control.
• fontcolor=None Text color. Defaults to foreground color.
• select_color=DARKBLUE Background color for selected item in list.
• callback=dolittle Callback function which runs when a list entry is picked.
• args=[] A list/tuple of arguments for above callback.

Methods:

• greyed_out Optional Boolean argument val=None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
• value Argument val=None. If a provided arg is a valid index into the list, that entry becomes current and the callback is executed. Always returns the index of the currently active entry.
• textvalue Argument text=None. If a string argument is provided and is in the control's list, that item becomes current. Normally returns the current string. If a provided arg did not match any list item, the control's state is not changed and None is returned.

If select is pressed when the Dropdown has focus, the list is displayed. The increase and decrease buttons move the list currency. If select is pressed after changing the currency the callback is triggered, the list is closed and the control will display the newly selected entry. If next or prev are pressed while the list is open, focus will move to the next widget. In this event the list will close and no selection change will be recognised: the control will show the element which was visible at the start and the callback will not run. Moving the focus is a means of cancelling any changes.

The callback's first argument is the dropdown instance followed by any args specified to the constructor. The currently selected item may be retrieved by means of the instance's value or textvalue methods.

Alternative approach

By default the Dropdown runs a single callback regardless of the element chosen. This can be changed by specifying elements such that each element comprises a 3-list or 3-tuple with the following contents:

1. String to display.
2. Callback.
3. Tuple of args (may be ()).

In this case constructor args callback and args must not be supplied. Args received by the callback functions comprise the Dropdown instance followed by any supplied args. The following is a complete example (minus initial import statements):

class BaseScreen(Screen):
    def __init__(self):
        def cb(dd, arg):
            print('Gas', arg)

        def cb_radon(dd, arg):
            print('Radioactive', arg)

        super().__init__()
        wri = CWriter(ssd, freesans20, GREEN, BLACK, verbose=False)
        els = (('hydrogen', cb, ('H2',)),
               ('helium', cb, ('He',)),
               ('neon', cb, ('Ne',)),
               ('xenon', cb, ('Xe',)), 
               ('radon', cb_radon, ('Ra',)))
        Dropdown(wri, 2, 2, elements = els,
                bdcolor = RED, fgcolor=RED, fontcolor = YELLOW)
        CloseButton(wri)


Screen.change(BaseScreen)

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6.9 DialogBox class

from gui.widgets import DialogBox  # File: dialog.py

An active dialog box. Auto generated dialogs contain only pushbutton instances, but user created dialogs may contain any widget.

This implements a modal dialog box based on a horizontal row of pushbuttons. Any button press will close the dialog. The caller can determine which button was pressed. The size of the buttons and the width of the dialog box are calculated from the strings assigned to the buttons. This ensures that buttons are evenly spaced and identically sized. Typically used for simple queries such as "yes/no/cancel".

Constructor positional args:

1. writer The Writer instance (defines font) to use.
2. row=20 Location on screen.
3. col=20

Mandatory keyword only arg:

• elements A list or tuple of 2-tuples. Each defines the text and color of a pushbutton, e.g. (('Yes', RED), ('No', GREEN)).

Optional keyword only args:

• label=None Text for an optional label displayed in the centre of the dialog box.
• bgcolor=DARKGREEN Background color of window.
• buttonwidth=25 Minimum width of buttons. In general button dimensions are calculated from the size of the strings in elements.
• closebutton=True If set, a close button will be displayed at the top RH corner of the dialog box.
• callback=dolittle
• args=[]

Classmethod (inherited from Screen):

• value(cls, val=None) The val arg can be any Python type.

The DialogBox is a Screen subclass. Pressing any button closes the dialog and sets the Screen value to the text of the button pressed or "Close" in the case of the close button. The outcome can therefore be tested by running Screen.value() or by implementing the callback. The latter receives the DialogBox instance as a first arg, followed by any args supplied to the constructor.

Note that dialog boxes can also be constructed manually, enabling more flexible designs. For example these might have widgets other than pushbuttons. The approach is to write a user subclass of Window. Example code may be found in gui/demos/screens.py.

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6.10 Textbox widget

from gui.widgets import Textbox  # File: textbox.py

Displays multiple lines of text in a field of fixed dimensions. Text may be clipped to the width of the control or may be word-wrapped. If the number of lines of text exceeds the height available, scrolling will occur. Access to text that has scrolled out of view may be achieved by calling a method. If the widget is instantiated as active scrolling may be performed using the increase and decrease buttons. The widget supports fixed and variable pitch fonts.

Constructor mandatory positional arguments:

1. writer The Writer instance (font and screen) to use.
2. row Location on screen.
3. col
4. width Width of the object in pixels.
5. nlines Number of lines of text to display. The object's height is determined from the height of the font:
   height in pixels = nlines*font_height
   As per all widgets the border is drawn two pixels beyond the control's boundary.

Keyword only arguments:

• fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
• bgcolor=None Background color of object. If None the Writer background default is used.
• bdcolor=False Color of border. If False no border will be drawn. If a color is provided, a border line will be drawn around the control.
• clip=True By default lines too long to display are right clipped. If False is passed, word-wrap is attempted. If the line contains no spaces it will be wrapped at the right edge of the window.
• active=False If True scrolling may be performed via the increase and decrease buttons.

Methods:

• append Args s, ntrim=None, line=None Append the string s to the display and scroll up as required to show it. By default only the number of lines which will fit on screen are retained. If an integer ntrim=N is passed, only the last N lines are retained; ntrim may be greater than can be shown in the control, hidden lines being accessed by scrolling.
  If an integer (typically 0) is passed in line the display will scroll to show that line.
• scroll Arg n Number of lines to scroll. A negative number scrolls up. If scrolling would achieve nothing because there are no extra lines to display, nothing will happen. Returns True if scrolling occurred, otherwise False.
• value No args. Returns the number of lines of text stored in the widget.
• clear No args. Clears all lines from the widget and refreshes the display.
• goto Arg line=None Fast scroll to a line. By default shows the end of the text. 0 shows the start.

Fast updates:
Rendering text to the screen is relatively slow. To send a large amount of text the fastest way is to perform a single append. Text may contain newline ('\n') characters as required. In that way rendering occurs once only.

ntrim__ If text is regularly appended to a Textbox its buffer grows, using RAM. The value of ntrim sets a limit to the number of lines which are retained, with the oldest (topmost) being discarded as required.

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6.11 Meter widget

This passive widget displays a single floating point value on a vertical linear scale. Optionally it can support data dependent callbacks.

from gui.widgets import Meter  # File: meter.py

The two styles of meter, both showing a value of 0.65. This passive widget provides a vertical linear meter display of values scaled between 0.0 and 1.0. In these examples each meter simply displays a data value.

This example has two data sensitive regions, a control region with hysteresis and an alarm region. Callbacks can run in response to specific changes in the Meter's value emulating data-dependent behaviour including alarms and controls (like thermostats) having hysteresis.

The class supports one or more Region instances. Visually these appear as colored bands on the scale. If the meter's value enters, leaves or crosses one of these bands a callback is triggered. This receives an arg indicating the nature of the change which caused the trigger. For example an alarm might be triggered when the value, initially below the region, enters it or crosses it. The alarm might be cleared on exit or if crossed from above. Hysteresis as used in thermostats is simple to implement. Examples of these techniques may be found in gui.demos.tstat.py.

Regions may be modified, added or removed programmatically.

Constructor mandatory positional args:

1. writer The Writer instance (defines font) to use.
2. row Location on screen.
3. col

Keyword only args:

• height=50 Height of meter.
• width=10 Width.
• fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
• bgcolor=BLACK Background color of meter. If None the Writer background is used.
• bdcolor=False Color of border. If False no border will be drawn. If a color is provided, a border line will be drawn around the control.
• ptcolor=None Color of meter pointer or bar. Default is foreground color.
• divisions=5 No. of graduations to show.
• label=None A text string will cause a Label to be drawn below the meter. An integer will create a Label of that width for later use.
• style=Meter.LINE The pointer is a horizontal line. Meter.BAR causes a vertical bar to be displayed. Much easier to read on monochrome displays.
• legends=None If a tuple of strings is passed, Label instances will be displayed to the right hand side of the meter, starting at the bottom. E.G. ('0.0', '0.5', '1.0')
• value=0 Initial value.

Methods:

1. value Args: n=None, color=None.
   • n should be a float in range 0 to 1.0. Causes the meter to be updated. Out of range values are constrained. If None is passed the meter is not updated.
   • color Updates the color of the bar or line if a value is also passed. None causes no change.
     Returns the current value.
2. text Updates the label if present (otherwise throws a ValueError). Args:
   • text=None The text to display. If None displays last value.
   • invert=False If true, show inverse text.
   • fgcolor=None Foreground color: if None the Writer default is used.
   • bgcolor=None Background color, as per foreground.
   • bdcolor=None Border color. As per above except that if False is passed, no border is displayed. This clears a previously drawn border.
3. del_region Arg: a Region instance. Deletes the region. No callback will run.

Legends

Depending on the font in use for legends additional space may be required above and below the Meter to display the top and bottom legends.

Example of use of Regions

# Instantiate Meter
ts = Meter(wri, row, sl.mcol + 5, ptcolor=YELLOW, height=100, width=15,
           style=Meter.BAR, legends=('0.0', '0.5', '1.0'))
# Instantiate two Regions and associate with the Meter instance.
reg = Region(ts, 0.4, 0.55, MAGENTA, ts_cb)
al = Region(ts, 0.9, 1.0, RED, al_cb)

The callback ts_cb will run in response to data values between 0.4 and 0.55: if the value enters that range having been outside it, if it leaves the range, or if successive values are either side of the range. The al_cb callback behaves similarly for data values between 0.9 and 1.0.

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6.11.1 Region class

from gui.widgets import Region  # File: region.py

Instantiating a Region associates it with a supporting widget (currently only a Meter). Constructor positional args are as follows:

• tstat The parent instance.
• vlo Low value (0 <= vlo <= 1.0).
• vhi High value (vlo < vhi <= 1.0).
• color For visible band.
• callback This receives two args, reg being the Region instance and reason, an integer indicating why the callback occurred (see below).
• args=() Optional additional tuple of positional args for the callback.

Method:

• adjust Args: vlo, vhi. Change the range of the Region. Constraints are as per the above constructor args.

Class variables (constants).

These define the reasons why a callback occurred. A change in the Tstat value or an adjustment of the Region values can trigger a callback. The value might change such that it enters or exits the region. Alternatively it might change from being below the region to above it: this is described as a transit. The following cover all possible options.

• EX_WB_IA Exit region. Was below before it entered. Is now above.
• EX_WB_IB Exit, was below, is below.
• EX_WA_IA Exit, was above, is above.
• EX_WA_IB Exit, was above, is below.
• T_IA Transit, is above (was below by definition of a transit).
• T_IB Transit, is below.
• EN_WA Entry, was above.
• EN_WB Entry, was below.

The following, taken from gui.demos.tstat.py is an example of a thermostat callback with hysteresis:

    def ts_cb(self, reg, reason):
        # Turn on if T drops below low threshold when it had been above high threshold. Or
        # in the case of a low going drop so fast it never registered as being within bounds
        if reason == reg.EX_WA_IB or reason == reg.T_IB:
            self.led.value(True)
        elif reason == reg.EX_WB_IA or reason == reg.T_IA:
            self.led.value(False)

Values for these constants enable them to be combined with the bitwise or operator if you prefer that coding style:

if reason & (reg.EX_WA_IB | reg.T_IB):  # Leaving region heading down

On instantiation of a Region callbacks do not run. The desirability of this is application dependent. If the user Screen is provided with an after_open method, this can be used to assign a value to the Tstat to cause region callbacks to run as appropriate.

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6.12 Slider and HorizSlider widgets

from gui.widgets import Slider, HorizSlider  # File: sliders.py

Different styles of slider.

These emulate linear potentiometers in order to display or control floating point values. A description of the user interface in the active case may be found in Floating Point Widgets.

Vertical Slider and horizontal HorizSlider variants are available. These are constructed and used similarly. The short forms (v) or (h) are used below to identify these variants.

Constructor mandatory positional args:

1. writer The Writer instance (defines font) to use.
2. row Location on screen.
3. col

Optional keyword only arguments:

• height Dimension of the bounding box. Default 100 pixels (v), 20 (h).
• width Dimension of the bounding box. Default 20 pixels (v), 100 (h).
• divisions=10 Number of graduations on the scale.
• legends=None A tuple of strings to display near the slider. These will be distributed evenly along its length, starting at the bottom (v) or left (h).
• fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
• bgcolor=None Background color of object. If None the Writer background default is used.
• fontcolor=None Text color. Defaults to foreground color.
• bdcolor=False Color of border. If False no border will be drawn. If a color is provided, a border line will be drawn around the control.
• slotcolor=None Color for the slot: this is a thin rectangular region in the centre of the control along which the slider moves. Defaults to the background color.
• prcolor=None If active, in precision mode the white focus border changes to yellow to for a visual indication. An alternative color can be provided. WHITE will defeat this change.
• callback=dolittle Callback function which runs whenever the control's value changes. If the control is active it also runs on instantiation. This enables dynamic color changes. Default is a null function.
• args=[] A list/tuple of arguments for above callback.
• value=0.0 The initial value: slider will be at the bottom (v), left (h).
• active=True Determines whether the control can accept user input.
• min_delta=0.01 Minimim value increment
• max_delta=0.1 Maximum value increment (long button presses)

Methods:

• greyed_out Optional Boolean argument val=None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
• value=None Optional float argument. If supplied the slider moves to show the new value and the callback is triggered. The method constrains the range to 0.0 to 1.0. The method always returns the control's value.
• color Mandatory arg color The control is rendered in the selected color. This supports dynamic color changes.

If instantiated as active, the floating point widget behaves as per section 1.12. When the widget has focus, increase and decrease buttons adjust the value. Brief presses cause small changes, longer presses cause accelerating change. A long press of select invokes high precision mode.

Callback

The callback receives an initial arg being the widget instance followed by any user supplied args. The callback can be a bound method, typically of a Screen subclass. The callback runs when the widget is instantiated and whenever the value changes. This enables dynamic color change. See gui/demos/active.py.

Legends

Depending on the font in use for legends additional space may be required around sliders to display all legends.

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6.13 Scale widget

from gui.widgets import Scale  # File: scale.py

This displays floating point data having a wide dynamic range, and optionally provides for user input of such values. It is modelled on old radios where a large scale scrolls past a small window having a fixed pointer. This enables a scale with (say) 200 graduations (ticks) to readily be visible on a small display, with sufficient resolution to enable the user to interpolate between ticks. Default settings enable estimation of a value to within about +-0.1%.

The Scale may be active or passive. A description of the user interface in the active case may be found in Floating Point Widgets.

The scale handles floats in range -1.0 <= V <= 1.0, however data values may be scaled to match any given range.

Legends for the scale are created dynamically as it scrolls past the window. The user may control this by means of a callback. Example code may be found in nano-gui which has a Scale whose value range is 88.0 to 108.0. A callback ensures that the display legends match the user variable. A further callback can enable the scale's color to change over its length or in response to other circumstances.

Constructor mandatory positional args:

1. writer The Writer instance (defines font) to use.
2. row Location on screen.
3. col

Optional keyword only arguments:

• ticks=200 Number of "tick" divisions on scale. Must be divisible by 2.
• value=0.0 Initial value.
• height=0 Default is a minimum height based on the font height.
• width=100
• fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
• bgcolor=None Background color of object. If None the Writer background default is used.
• bdcolor=None Color of border, default fgcolor. If False no border will be drawn. If a color is provided, a border line will be drawn around the control.
• prcolor=None If active, in precision mode the white focus border changes to yellow to for a visual indication. An alternative color can be provided. WHITE will defeat this change.
• pointercolor=None Color of pointer. Defaults to .fgcolor.
• fontcolor=None Color of legends. Default fgcolor.
• legendcb=None Callback for populating scale legends (see below).
• tickcb=None Callback for setting tick colors (see below).
• callback=dolittle Callback function which runs when the user moves the scale or the value is changed programmatically. If the control is active it also runs on instantiation. Default is a null function.
• args=[] A list/tuple of arguments for above callback.
• active=False By default the widget is passive. By setting active=True the widget can acquire focus; its value can then be adjusted with the increase and decrease buttons.

Methods:

• greyed_out Optional Boolean argument val=None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
• value=None Set or get the current value. Always returns the current value. A passed float is constrained to the range -1.0 <= V <= 1.0 and becomes the Scale's current value. The Scale is updated. Passing None enables reading the current value, but see note below on precision.

For example code see gui/demos/active.py.

Control algorithm

If instantiated as active, the floating point widget behaves as per section 1.12. When the widget has focus, increase and decrease buttons adjust the value. Brief presses cause small changes, longer presses cause accelerating change. A long press of select invokes high precision mode.

Callback

The callback receives an initial arg being the widget instance followed by any user supplied args. The callback can be a bound method, typically of a Screen subclass. The callback runs when the widget is instantiated and whenever the value changes. This enables dynamic color change.

Callback legendcb

The display window contains 20 ticks comprising two divisions; by default a division covers a range of 0.1. A division has a legend at the start and end whose text is defined by the legendcb callback. If no user callback is supplied, legends will be of the form 0.3, 0.4 etc. User code may override these to cope with cases where a user variable is mapped onto the control's range. The callback takes a single float arg which is the value of the tick (in range -1.0 <= v <= 1.0). It must return a text string. An example from ths nano-gui demo shows FM radio frequencies:

def legendcb(f):
    return '{:2.0f}'.format(88 + ((f + 1) / 2) * (108 - 88))

The above arithmetic aims to show the logic. It can (obviously) be simplified.

Callback tickcb

This callback enables the tick color to be changed dynamically. For example a scale might change from green to orange, then to red as it nears the extremes. The callback takes two args, being the value of the tick (in range -1.0 <= v <= 1.0) and the default color. It must return a color. This example is taken from the scale.py demo:

def tickcb(f, c):
    if f > 0.8:
        return RED
    if f < -0.8:
        return BLUE
    return c

Increasing the ticks value

This increases the precision of the display.

It does this by lengthening the scale while keeping the window the same size, with 20 ticks displayed. If the scale becomes 10x longer, the value diference between consecutive large ticks and legends is divided by 10. This means that the tickcb callback must return a string having an additional significant digit. If this is not done, consecutive legends will have the same value.

Precision

For performance reasons the control stores values as integers. This means that if you set value and subsequently retrieve it, there may be some loss of precision. Each visible division on the control represents 10 integer units.

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6.14 ScaleLog widget

from gui.widgets import ScaleLog  # File: scale_log.py

This displays floating point values with extremely wide dynamic range and optionally enables their input. The dynamic range is handled by means of a base 10 logarithmic scale. In other respects the concept is that of the Scale class.

The control is modelled on old radios where a large scale scrolls past a small window having a fixed pointer. The use of a logarithmic scale enables the value to span a range of multiple orders of magnitude.

The Scale may be active or passive. A description of the user interface in the active case may be found in Floating Point Widgets. Owing to the logarithmic nature of the widget, the changes discussed in that reference are multiplicative rather than additive. Thus a long press of increase will multiply the widget's value by a progressively larger factor, enabling many decades to be traversed quickly.

Legends for the scale are created dynamically as it scrolls past the window, with one legend for each decade. The user may control this by means of a callback, for example to display units, e.g. 10MHz. A further callback enables the scale's color to change over its length or in response to other circumstances.

The scale displays floats in range 1.0 <= V <= 10**decades where decades is a constructor arg. The user may readily scale these so that a control having a range of 1-10,000 controls a user value from 1e-6 to 1e-2 while displaying ticks labelled 1μs, 10μs, 100μs, 1ms and 10ms.

Constructor mandatory positional args:

1. writer The Writer instance (defines font) to use.
2. row Location on screen.
3. col

Keyword only arguments (all optional):

• decades=5 Defines the control's maximum value (i.e. 10**decades).
• value=1.0 Initial value for control. Will be constrained to 1.0 <= value <= 10**decades if outside this range.
• height=0 Default is a minimum height based on the font height.
• width=160
• fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
• bgcolor=None Background color of object. If None the Writer background default is used.
• bdcolor=None Color of border, default fgcolor. If False no border will be drawn. If a color is provided, a border line will be drawn around the control.
• prcolor=None If active, in precision mode the white focus border changes to yellow to for a visual indication. An alternative color can be provided. WHITE will defeat this change.
• pointercolor=None Color of pointer. Defaults to .fgcolor.
• fontcolor=None Color of legends. Default WHITE.
• legendcb=None Callback for populating scale legends (see below).
• tickcb=None Callback for setting tick colors (see below).
• callback=dolittle Callback function which runs when the user moves the scale or the value is changed programmatically. If the control is active it also runs on instantiation. Default is a null function.
• args=[] A list/tuple of arguments for above callback. The callback's arguments are the ScaleLog instance, followed by any user supplied args.
• delta=0.01 This determines the smallest amount of change which can be achieved with a brief button press. See Control Algorithm below.
• active=False Determines whether the widget accepts user input.

Methods:

• value=None Set or get the current value. Always returns the current value. A passed float is constrained to the range 1.0 <= V <= 10**decades and becomes the control's current value. The ScaleLog is updated. Always returns the control's current value.
• greyed_out Optional Boolean argument val=None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.

Class variable:

• encoder_rate=5 If the hardware uses an encoder, this determines the rate of change when the value is adjusted. Increase to raise the rate.

For example code see gui/demos/active.py.

Control algorithm

If instantiated as active, the floating point widget behaves as per section 1.12. When the widget has focus, increase and decrease buttons adjust the value. Brief presses cause small changes, longer presses cause accelerating change. A long press of select invokes high precision mode.

In normal mode, the amount of change caused by a brief button press is controlled by the constructor arg delta; the choice of this value represents a compromise between precision and usability.

Owing to the logarithmic nature of the control, a small positive change is defined by multiplication of the value by (1 + delta) and a negative change corresponds to division by (1 + delta). In precision mode delta is reduced by a factor of 10.

Callback

The callback receives an initial arg being the widget instance followed by any user supplied args. The callback can be a bound method, typically of a Screen subclass. The callback runs when the widget is instantiated and whenever the value changes. This enables dynamic color change.

Callback legendcb

The start of each decade is marked by a long "tick" with a user-definable text label. By default it will display a number corresponding to the value at that tick (of form 10**n where n is an integer), but this can be overridden to display values such as "10MHz". The following is a simple example from the scale_ctrl_test demo:

def legendcb(f):
    if f < 999:
        return '{:<1.0f}'.format(f)
    return '{:<1.0f}K'.format(f/1000)

Callback tickcb

This callback enables the tick color to be changed dynamically. For example a scale might change from green to orange, then to red as it nears the extremes. The callback takes two args, being the value of the tick (of form 10**n where n is an integer) and the default color. It must return a color. This example is taken from the scale_ctrl_test demo:

def tickcb(f, c):
    if f > 30000:
        return RED
    if f < 10:
        return BLUE
    return c

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6.15 Dial widget

from gui.widgets import Dial, Pointer  # File: dial.py

A Dial is a passive widget. It presents a circular display capable of displaying an arbitrary number of vectors; each vector is represented by a Pointer instance. The format of the display may be chosen to resemble an analog clock or a compass. In the CLOCK case a pointer resembles a clock's hand extending from the centre towards the periphery. In the COMPASS case pointers are chevrons extending equally either side of the circle centre.

In both cases the length, angle and color of each Pointer may be changed dynamically. A Dial can include an optional Label at the bottom which may be used to display any required text.

In use, a Dial is instantiated. Then one or more Pointer objects are instantiated and assigned to it. The Pointer.value method enables the Dial to be updated affecting the length, angle and color of the Pointer. Pointer values are complex numbers.

Dial class

Constructor mandatory positional args:

1. writer The Writer instance (defines font) to use.
2. row Location on screen.
3. col

Keyword only args:

• height=100 Height and width of dial.
• fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
• bgcolor=None Background color of object. If None the Writer background default is used.
• bdcolor=False Color of border. If False no border will be drawn. If a color is provided, a border line will be drawn around the control.
• ticks=4 No. of gradutions to show.
• label=None A text string will cause a Label to be drawn below the meter. An integer will create a Label of that width for later use.
• style=Dial.CLOCK Pointers are drawn from the centre of the circle as per the hands of a clock. Dial.COMPASS causes pointers to be drawn as arrows centred on the control's centre. Arrow tail chevrons are suppressed for very short pointers.
• pip=None Draws a central dot. A color may be passed, otherwise the foreground color will be used. If False is passed, no pip will be drawn. The pip is suppressed if the shortest pointer would be hard to see.

Method:

1. text Updates the label if present (otherwise throws a ValueError). Args:
   • text=None The text to display. If None displays last value.
   • invert=False If true, show inverse text.
   • fgcolor=None Foreground color: if None the Writer default is used.
   • bgcolor=None Background color, as per foreground.
   • bdcolor=None Border color. As per above except that if False is passed, no border is displayed. This clears a previously drawn border.

When a Pointer is instantiated it is assigned to the Dial by the Pointer constructor.

Pointer class

Constructor arg:

1. dial The Dial instance on which it is to be dsplayed.

Methods:

1. value Args:
   • v=None The value is a complex number. A magnitude exceeding unity is reduced (preserving phase) to constrain the Pointer within the unit circle.
   • color=None By default the pointer is rendered in the foreground color of the parent Dial. Otherwise the passed color is used.
     Returns the current value.

Typical usage:

from hardware_setup import ssd  # Create a display instance
import uasyncio as asyncio
import cmath
from gui.core.ugui import Screen
from gui.core.writer import CWriter
from gui.core.colors import *

from gui.widgets import Dial, Pointer, CloseButton
import gui.fonts.freesans20 as freesans20

async def run(dial):
    hrs = Pointer(dial)
    mins = Pointer(dial)
    hrs.value(0 + 0.7j, RED)
    mins.value(0 + 0.9j, YELLOW)
    dm = cmath.exp(-1j * cmath.pi / 30)  # Rotate by 1 minute
    dh = cmath.exp(-1j * cmath.pi / 1800)  # Rotate hours by 1 minute
    # Twiddle the hands: see vtest.py for an actual clock
    while True:
        await asyncio.sleep_ms(200)
        mins.value(mins.value() * dm, RED)
        hrs.value(hrs.value() * dh, YELLOW)

class BaseScreen(Screen):

    def __init__(self):
        super().__init__()
        wri = CWriter(ssd, freesans20, GREEN, BLACK, verbose=False)
        dial = Dial(wri, 5, 5, ticks = 12, bdcolor=None)
        self.reg_task(run(dial))
        CloseButton(wri)

Screen.change(BaseScreen)

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6.16 Knob widget

from gui.widgets import Knob  # File: knob.py

Rightmost example has no border and 270° travel. Others have 360°.

This emulates a rotary control capable of being rotated through a predefined arc in order to display or set a floating point variable. A Knob may be active or passive. A description of the user interface in the active case may be found in Floating Point Widgets.

Constructor mandatory positional args:

1. writer The Writer instance (defines font) to use.
2. row Location on screen.
3. col

Optional keyword only arguments:

• height=70 Dimension of the square bounding box.
• arc=TWOPI Movement available. Default 2*PI radians (360 degrees). May be reduced, e.g. to provide a 270° range of movement.
• ticks=9 Number of graduations around the dial.
• value=0.0 Initial value. By default the knob will be at its most counter-clockwise position.
• fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
• bgcolor=None Background color of object. If None the Writer background default is used.
• color=None Fill color for the control knob. Default: no fill.
• bdcolor=False Color of border. If False no border will be drawn. If a color is provided, a border line will be drawn around the control.
• prcolor=None If active, in precision mode the white focus border changes to yellow for a visual indication. An alternative color can be provided. WHITE defeats this change; False disables precision mode.
• callback=dolittle Callback function runs when the user moves the knob or the value is changed programmatically.
• args=[] A list/tuple of arguments for above callback.
• active=True Enable user input via the increase and decrease buttons.

Methods:

• greyed_out Optional Boolean argument val=None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
• value Optional argument val. If set, adjusts the pointer to correspond to the new value. The move callback will run. The method constrains the range to 0.0 to 1.0. Always returns the control's value.

Callback

The callback receives an initial arg being the widget instance followed by any user supplied args. The callback can be a bound method, typically of a Screen subclass. The callback runs when the widget is instantiated and whenever the value changes. This enables dynamic color change.

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6.17 Adjuster widget

from gui.widgets import Adjuster, FloatAdj  # File: adjuster.py

Four examples paired with Labels. An example of two Adjuster instances setting a vector.

The Adjuster is a space saving version of the Knob. It is normally paired with a Label which provides user feedback of the value. It has a range of 0.0 to 1.0 and a visual arc of 270°. User code can provide arbitrary scaling or nonlinear operation. This is demonstrated in demos/adjuster.py. The widget was inspired by discussions with the author of this project.

Constructor mandatory positional args:

1. writer The Writer instance. This defines the control's height.
2. row Location on screen.
3. col

Optional keyword only arguments:

• value=0.0 Initial value. By default the knob will be at its most counter-clockwise position.
• fgcolor=None Color of foreground (the control itself). If None the Writer foreground default is used.
• bgcolor=None Background color of object. If None the Writer background default is used.
• color=None Fill color for the control knob. Default: no fill.
• prcolor=None In precision mode the white focus border changes to yellow for a visual indication. An alternative color can be provided. WHITE defeats the change; False disables precision mode.
• callback=dolittle Callback function runs when the user moves the knob or the value is changed programmatically.
• args=[] A list/tuple of arguments for above callback.

Methods:

• greyed_out Optional Boolean argument val=None. If None returns the current 'greyed out' status of the control. Otherwise enables or disables it, showing it in its new state.
• value Optional argument val. If set, adjusts the pointer to correspond to the new value. The move callback will run. The method constrains the range to 0.0 to 1.0. Always returns the control's value.

Callback

The callback receives an initial arg being the widget instance followed by any user supplied args. The callback can be a bound method, typically of a Screen subclass. The callback runs when the widget is instantiated and whenever the value changes. Typically the callback will adjust the text displayed on a linked label.

A numeric entry device

The file widgets/adjuster.py includes an example class which combines an Adjuster with one or two Label instances. The Adjuster changes the displayed value in the Label to its left. Its use is illustrated in demos/adjuster.py. The class can be used as a template for a user class, which may have a different layout on screen. It supports arbitrary mapping and number formatting on a per-instance basis. See code comments for further details.

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6.18 Menu class

from gui.widgets import Menu  # File: menu.py

The Menu class enables the creation of single or multiple level menus. The top level of the menu comprises a row of Button instances at the top of the physical screen. Each button can either call a callback or instantiate a dropdown menu comprising the second menu level.

Each item on a dropdown menu can invoke either a callback or a lower level menu.

Constructor mandatory positional arg:

1. writer The Writer instance (defines font) to use.

Keyword only args:

• height=25 Height of top level menu buttons.
• bgcolor=None Background color of buttons and dropdown.
• fgcolor=None Foreground color.
• textcolor=None Text color.
• select_color=DARKBLUE Background color of selected item on dropdown menu.
• args This should be a tuple containing a tuple of args for each entry in the top level menu. Each tuple should be of one of two forms:

1. (text, cb, (args,)) A single-level entry: the top level Button with text text runs the callback cb with positional args defined by the supplied tuple (which may be ()). The callback receives an initial arg being the Button instance.
2. (text, (element0, element1,...)) In this instance the top level Button triggers a dropdown menu defined by data in the elements tuple.

Each element in the elements tuple is a tuple defining a menu item. This can take two forms, each of which has the text for the menu item as the first value:

1. (text, cb, (args,)) The element triggers callback cb with positional args defined by the supplied tuple (which may be ()). The callback receives an initial arg being the Listbox instance which corresponds to the parent dropdown menu.
2. (text, (elements,)) This element triggers a submenu with a recursive instance of elements.

The following (from gui/demos/menui.py) is complete apart from initial import statements. It illustrates a 3-level menu.

class BaseScreen(Screen):

    def __init__(self):
        def cb(button, n):
            print('Help callback', n)

        def cb_sm(lb, n):
            print('Submenu callback', lb.value(), lb.textvalue(), n)

        super().__init__()
        metals2 = (('Gold', cb_sm, (10,)),
                   ('Silver', cb_sm, (11,)),
                   ('Iron', cb_sm, (12,)),
                   ('Zinc', cb_sm, (13,)),
                   ('Copper', cb_sm, (14,)))  # Level 3

        gases = (('Helium', cb_sm, (0,)),
                 ('Neon', cb_sm, (1,)),
                 ('Argon', cb_sm, (2,)),
                 ('Krypton', cb_sm, (3,)),
                 ('Xenon', cb_sm, (4,)),
                 ('Radon', cb_sm, (5,)))  # Level 2

        metals = (('Lithium', cb_sm, (6,)),
                  ('Sodium', cb_sm, (7,)),
                  ('Potassium', cb_sm, (8,)),
                  ('Rubidium', cb_sm, (9,)),
                  ('More', metals2))  # Level 2

        mnu = (('Gas', gases),
               ('Metal', metals),
               ('Help', cb, (2,)))  # Top level 1

        wri = CWriter(ssd, font, GREEN, BLACK, verbose=False)
        Menu(wri, bgcolor=BLUE, textcolor=WHITE, args = mnu)
        CloseButton(wri)

Screen.change(BaseScreen)

The code

        mnu = (('Gas', gases),
               ('Metal',metals),
               ('Help', cb, (2,)))

defines the top level, with the first two entries invoking submenus and the third running a callback cb with 2 as an arg.

This produces a second level menu with one entry ('More') invoking a third level (metals2):

        metals = (('Lithium', cb_sm, (6,)),
                  ('Sodium', cb_sm, (7,)),
                  ('Potassium', cb_sm, (8,)),
                  ('Rubidium', cb_sm, (9,)),
                  ('More', metals2))

The other entries all run cb_sm with a different arg. They could each run a different callback if the application required it.

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6.19 BitMap Widget

from gui.widgets import BitMap  # File: bitmap.py

This renders a monochrome bitmap stored in a file to a rectangular region. The bitmap file format is C source code generated by the Linux bitmap editor. The bitmap may be rendered in any color. Data and colors can be changed at run time. The widget is intended for larger bitmaps and is designed to minimise RAM usage at cost of performance. For fast updates of smaller bitmaps consider using an icon font.

Constructor mandatory positional args:

1. writer A Writer instance.
2. row Location on screen.
3. col
4. height Image height in pixels. Dimensions must exactly match the image file.
5. width Image width in pixels.

Keyword only args:

• fgcolor=None Foreground (1) color of image.
• bgcolor=None Background (0) color.
• bdcolor=RED Border color.

Methods:__

• value mandatory arg fn path to an image file. Causes the BitMap image to be updated from the file. Blocks for a period depending on filesystem performance.
• color args fgcolor=None, bgcolor=None. Causes the image colors to be changed. The file will be re-read and the image updated.

Beacuse of the use of file storage when an update occurs there will be a brief "dead time" when the GUI is unresponsive. This is not noticeable if the image is displayed when a screen initialises, or if it changes in response to a user action. Use in animations is questionable.

See gui/demos/bitmap.py for a usage example.

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6.20 QRMap Widget

from gui.widgets import QRMap  # File: qrcode.py

This renders QR codes generated using the uQR application. Images may be scaled to render them at larger sizes. Please see the notes below on performance and RAM usage.

Constructor positional args:

1. writer A Writer instance.
2. row Location on screen.
3. col
4. version=4 Defines the size of the image: see below.
5. scale=1

Keyword only args:

• bdcolor=RED Border color.
• buf=None Allows use of a pre-allocated image buffer.

Methods:__

• value mandatory arg text a string for display as a QR code. This method can throw a ValueError if the string cannot be accommodated in the chosen code size (i.e. version).
• __call__ Synonym for value.

Static Method:__

• make_buffer args version, scale. Returns a buffer big enough to hold the QR code bitmap. Use of this is optional: it is a solution if memory errors are encountered when instantiating a QRMap.

Note on image sizes. The size of a QR code bitmap depends on the version and scale parameters according to this formula:
edge_length_in_pixels = (4 * version + 17) * scale
To this must be added a mandatory 4 pixel border around every edge. So the height and width occupied on screen is:
dimension = (4 * version + 25) * scale

Performance
The uQR get_matrix() method blocks: in my testing for about 750ms. A QRMap buffers the scaled matrix and renders it using bit blitting. Blocking by QRMap methods is minimal; refreshing a screen with the same contents is fast.

The uQR library is large, and compiling it uses a substantial amount of RAM. If memory errors are encountered try cross-compiling or the use of frozen byte code.

See gui/demos/qrcode.py for a usage example. The demo expects uQR.py to be located in the root directory of the target.

Contents

7. Graph Plotting

from gui.widgets.graph import PolarGraph, PolarCurve, CartesianGraph, Curve, TSequence

Realtime time sequence simulation.

For example code see gui/demos/plot.py.

7.1 Concepts

Data for Cartesian graphs constitutes a sequence of x, y pairs, for polar graphs it is a sequence of complex z values. The module supports three common cases:

1. The dataset to be plotted is complete at the outset.
2. Arbitrary data arrives gradually and needs to be plotted as it arrives.
3. One or more y values arrive gradually. The X axis represents time. This is a simplifying case of 2.

7.1.1 Graph classes

A user program first instantiates a graph object (PolarGraph or CartesianGraph). This creates an empty graph image upon which one or more curves may be plotted. Graphs are passive widgets so cannot accept user input.

7.1.2 Curve classes

The user program then instantiates one or more curves (Curve or PolarCurve) as appropriate to the graph. Curves may be assigned colors to distinguish them.

A curve is plotted by means of a user defined populate generator. This assigns points to the curve in the order in which they are to be plotted. The curve will be displayed on the graph as a sequence of straight line segments between successive points.

Where it is required to plot realtime data as it arrives, this is achieved via calls to the curve's point method. If a prior point exists it causes a line to be drawn connecting the point to the last one drawn.

7.1.3 Coordinates

PolarGraph and CartesianGraph objects are subclassed from Widget and are positioned accordingly by row and col with a 2-pixel outside border. The coordinate system within a graph conforms to normal mathematical conventions.

Scaling is provided on Cartesian curves enabling user defined ranges for x and y values. Points lying outside of the defined range will produce lines which are clipped at the graph boundary.

Points on polar curves are defined as Python complex types and should lie within the unit circle. Points which are out of range may be plotted beyond the unit circle but will be clipped to the rectangular graph boundary.

Contents

7.2 Graph classes

7.2.1 Class CartesianGraph

Constructor.
Mandatory positional arguments:

1. writer A CWriter instance.
2. row Position of the graph in screen coordinates.
3. col

Keyword only arguments (all optional):

• height=90 Dimension of the bounding box.
• width=110 Dimension of the bounding box.
• fgcolor=None Color of the axis lines. Defaults to Writer foreground color.
• bgcolor=None Background color of graph. Defaults to Writer background.
• bdcolor=None Border color. If False no border is displayed. If None a border is shown in the foreground color. If a color is passed, it is used.
• gridcolor=None Color of grid. Default: Writer foreground color.
• xdivs=10 Number of divisions (grid lines) on x axis.
• ydivs=10 Number of divisions on y axis.
• xorigin=5 Location of origin in terms of grid divisions.
• yorigin=5 As xorigin. The default of 5, 5 with 10 grid lines on each axis puts the origin at the centre of the graph. Settings of 0, 0 would be used to plot positive values only.

Method:

• show No args. Redraws the empty graph. Used when plotting time sequences.

7.2.2 Class PolarGraph

Constructor.
Mandatory positional arguments:

1. writer A CWriter instance.
2. row Position of the graph in screen coordinates.
3. col

Keyword only arguments (all optional):

• height=90 Dimension of the square bounding box.
• fgcolor=None Color of the axis lines. Defaults to Writer foreground color.
• bgcolor=None Background color of graph. Defaults to Writer background.
• bdcolor=None Border color. If False no border is displayed. If None a border is shown in the Writer foreground color. If a color is passed, it is used.
• gridcolor=None Color of grid. Default: Writer foreground color.
• adivs=3 Number of angle divisions per quadrant.
• rdivs=4 Number radius divisions.

Method:

• show No args. Redraws the empty graph.

Contents

7.3 Curve classes

7.3.1 Class Curve

The Cartesian curve constructor takes the following positional arguments:

Mandatory arguments:

1. graph The CartesianGraph instance.
2. color If None is passed, the graph foreground color is used.

Optional arguments:
3. populate=None A generator to populate the curve. See below.
4. origin=(0,0) 2-tuple containing x and y values for the origin. Provides for an optional shift of the data's origin.
5. excursion=(1,1) 2-tuple containing scaling values for x and y.

Methods:

• point Arguments x, y. Defaults None. Adds a point to the curve. If a prior point exists a line will be drawn between it and the current point. If a point is out of range or if either arg is None no line will be drawn. Passing no args enables discontinuous curves to be plotted. This method is normally used for real time plotting.

The populate generator may take zero or more positional arguments. It should repeatedly yield x, y values before returning. Where a curve is discontinuous None, None may be yielded: this causes the line to stop. It is resumed when the next valid x, y pair is yielded.

If populate is not provided the curve may be plotted by successive calls to the point method. This may be of use where data points are acquired in real time, and realtime plotting is required. See class RTRect in gui/demos/plot.py.

Scaling

By default, with symmetrical axes, x and y values are assumed to lie between -1 and +1.

To plot x values from 1000 to 4000 we would set the origin x value to 1000 and the excursion x value to 3000. The excursion values scale the plotted values to fit the corresponding axis.

7.3.2 Class PolarCurve

The constructor takes the following positional arguments:

Mandatory arguments:

1. graph The PolarGraph instance.
2. color

Optional arguments:
3. populate=None A generator to populate the curve. See below.

Methods:

• point Argument z=None. Normally a complex. Adds a point to the curve. If a prior point exists a line will be drawn between it and the current point. If the arg is None no line will be drawn. Passing no args enables discontinuous curves to be plotted. Lines are clipped at the square region bounded by (-1, -1) to (+1, +1).

The populate generator may take zero or more positional arguments. It should yield a complex z value for each point before returning. Where a curve is discontinuous a value of None may be yielded: this causes plotting to stop. It is resumed when the next valid z point is yielded.

If populate is not provided the curve may be plotted by successive calls to the point method. This may be of use where data points are acquired in real time, and realtime plotting is required. See class RTPolar in gui/demos/plot.py.

Scaling

Complex points should lie within the unit circle to be drawn within the grid.

Contents

7.4 Class TSequence

A common task is the acquisition and plotting of real time data against time, such as hourly temperature and air pressure readings. This class facilitates this. Time is on the x-axis with the most recent data on the right. Older points are plotted to the left until they reach the left hand edge when they are discarded. This is akin to old fashioned pen plotters where the pen was at the rightmost edge (corresponding to time now) with old values scrolling to the left with the time axis in the conventional direction.

The user instantiates a graph with the X origin at the right hand side and then instantiates one or more TSequence objects. As each set of data arrives it is appended to its TSequence using the add method. See the example below.

The constructor takes the following args:

Mandatory arguments:

1. graph The CartesianGraph instance.
2. color
3. size Integer. The number of time samples to be plotted. See below.

Optional arguments:
4. yorigin=0 These args provide scaling of Y axis values as per the Curve class. 5 yexc=1

Method:

1. add Arg v the value to be plotted. This should lie between -1 and +1 unless scaling is applied.

Note that there is little point in setting the size argument to a value greater than the number of X-axis pixels on the graph. It will work but RAM and execution time will be wasted: the constructor instantiates an array of floats of this size.

Each time a data set arrives the graph should be cleared and a data value is added to each TSequence instance. The following (slightly simplified) is taken from gui/demos/plot.py and simulates the slow arrival of sinusoidal values.

class TSeq(Screen):
    def __init__(self):
        super().__init__()
        self.g = CartesianGraph(wri, 2, 2, xorigin = 10, fgcolor=GREEN,
                                gridcolor=LIGHTGREEN, bdcolor=False)

    def after_open(self):  # After graph has been drawn
        self.reg_task(self.run(self.g), True)  # Cancel on screen change

    async def run(self, g):
        await asyncio.sleep_ms(0)
        tsy = TSequence(g, YELLOW, 50)
        tsr = TSequence(g, RED, 50)
        t = 0
        while True:
            g.show()  # Redraw the empty graph
            tsy.add(0.9*math.sin(t/10))
            tsr.add(0.4*math.cos(t/10))  # Plot the new curves
            await asyncio.sleep_ms(400)
            t += 1

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8. ESP32 touch pads

On ESP32 physical buttons may be replaced with touch pads. Buttons and pads cannot be mixed, but it is possible to use three pads with an encoder.

The only change required to use touch pads is in hardware_setup.py. Pin instances must be chosen from ones supporting the TouchPad class - see official docs. The Pin constructor may be called with a single arg being the pin number.

The following illustrates the end of a setup file for an application with five touchpads:

# Set up for display driver omitted
ssd = SSD(spi, pcs, pdc, prst)

from gui.core.ugui import Display, quiet
# quiet()
# Define control pins - no pullups.
nxt = Pin(13)  # Move to next control
sel = Pin(14)  # Operate current control
prev = Pin(15)  # Move to previous control
increase = Pin(33)  # Increase control's value
decrease = Pin(32)  # Decrease control's value
# Create a Display instance and assign to display.
display = Display(ssd, nxt, sel, prev, increase, decrease, False, 80)

The final two constructor args are:

• encoder=False No encoder being used in this example.
• touch=80 Use touch interface with a threshold of 80%.

The touch value determines the level from machine.TouchPad.read() at which a touch is determined to have occurred. In the above fragment a value of 80 is passed. Assume the untouched value from TouchPad.read() is 1020. If a value below 80% of 1020 = 816 is read, a touch is deemed to have occurred. Further docs on pushbutton.py may be found here.

9. Realtime applications

Screen refresh is performed in a continuous loop with yields to the scheduler. In normal applications this works well, however a significant proportion of processor time is spent performing a blocking refresh. A means of synchronising refresh to other tasks is provided, enabling the application to control the screen refresh. This is done by means of two Event instances. The refresh task operates as below (code simplified to illustrate this mechanism).

class Screen:
    rfsh_start = Event()  # Refresh pauses until set (set by default).
    rfsh_done = Event()  # Flag a user task that a refresh was done.

    @classmethod
    async def auto_refresh(cls):
        cls.rfsh_start.set()
        while True:
            await cls.rfsh_start.wait()
            ssd.show()  # Synchronous (blocking) refresh.
            # Flag user code.
            cls.rfsh_done.set()
            await asyncio.sleep_ms(0)  # Let user code respond to event

By default the rfsh_start event is permanently set, allowing refresh to free run. User code can clear this event to delay refresh. The rfsh_done event can signal to user code that refresh is complete. As an example of simple usage, the following, if awaited, pauses until a refresh is complete and prevents another from occurring.

    async def refresh_and_stop(self):
        Screen.rfsh_start.set()  # Allow refresh
        Screen.rfsh_done.clear()  # Enable completion flag
        await Screen.rfsh_done.wait()  # Wait for a refresh to end
        Screen.rfsh_start.clear()  # Prevent another.

The demo gui/demos/audio.py provides example usage.

10 ePaper displays

In general ePaper displays do not work well with micro-gui because refresh is slow (seconds) and visually intrusive. Some displays support partial refresh which is faster (hundreds of ms) and non-intrusive. The penalty is "ghosting" where pixels which change from black to white do so imperfectly, leaving a grey trace behind. The degree of ghosting varies between display types.

The Waveshare pico_epaper_42 has quite a low level of ghosting. A full refresh takes about 2.1s and partial about 740ms. In use there is a visible lag between operating a user control and a visible response, but it is usable. Currently this is the only fully supported ePaper display.

It has a socket for a Pico or Pico W, but also comes with a cable suitable for connecting to any host. The hardware_setup.py should be copied or adapted from setup_examples/pico_epaper_42_pico.py. If using the socket, default args may be used (see code comment).

Some attention to detail is required to handle the refresh characteristics. The application must wait for the initial full refresh (which occurs automatically) before putting the display into partial mode. This is done by the screen constructor issuing

        asyncio.create_task(set_partial())

to run

async def set_partial():  # Ensure 1st refresh is a full refresh
    await Screen.rfsh_done.wait()  # Wait for first refresh to end
    ssd.set_partial()

The application then runs in partial mode with a reasonably quick and visually satisfactory response to user inputs such as button events. See the epaper demo.

It is likely that applications will provide a full refresh method to clear any ghosting. The demo provides for a full refresh via the reset button. A full refresh should be done as follows:

async def full_refresh():
    Screen.rfsh_done.clear()  # Enable completion flag
    await Screen.rfsh_done.wait()  # Wait for a refresh to end
    ssd.set_full()
    Screen.rfsh_done.clear()  # Re-enable completion flag
    await Screen.rfsh_done.wait()  # Wait for a single full refresh to end
    ssd.set_partial()  # Subsequent refreshes are partial

The driver for the supported display uses 1-bit color mapping: this means that greying-out has no visible effect. Greyed-out controls cannot accept the focus and are therefore disabled but appearance is unchanged. nano-gui has a 2-bit driver which supports greyscales, but there is no partial support so this is unsuitable for micro_gui.

Contents

Appendix 1 Application design

Tab order and button layout

The "tab order" of widgets on a Screen is the order with which they acquire focus with successive presses of the Next button. It is determined by the order in which they are instantiated. Tab order is important for usability but instantiating in the best order can conflict with program logic. This happens if a widget's callback refers to others not yet instantiated. See demos dropdown.py and linked_sliders.py for one solution.

The obvious layout for the physical buttons is as per a joystick:

This works well with many screen layouts, if the tab order is considered in the layout of the screen. It works well with most widgets including vertical ones such as the Slider. With horizontal widgets such as Scale controls it can be counter intuitive because the horizontal layout does not match the position of the increase and decrease buttons. A different physical layout may be preferred.

The apparently obvious solution of designing a vertical Scale is tricky owing to the fact that the length of the internal text can be substantial and variable.

Encoder interface

This alternative interface comprises two buttons Next and Prev with an an encoder such as this one. Selection occurs when the knob is pressed, and movement when it is rotated. This can be more intuitive, particularly with horizontally oriented controls.

This is the pinout of the Adafruit encoder as viewed from the top, with connections to pins passed to the Display constructor as sel (select), up (increase) and down (decrease).

If an encoder operates in the wrong direction, Increase and Decrease pins should be transposed (physically or logically in hardware_setup.py).

Screen layout

Widgets are positioned using absolute row and col coordinates. These may optionally be calculated using the metrics of other widgets. This facilitates relative positioning which can make layouts easier to modify. Such layouts can also automatically adapt to changes of fonts. To simplify this, all widgets have the following bound variables, which should be considered read-only:

• height As specified. Does not include border.
• width Ditto.
• mrow Maximum absolute row occupied by the widget (including border).
• mcol Maximum absolute col occupied by the widget (including border).

A further aid to metrics is the Writer method .stringlen(s). This takes a string as its arg and returns its length in pixels when rendered using that Writer instance's font.

The mrow and mcol values enable other widgets to be positioned relative to the one previously instantiated. In the cases of sliders, Dial and Meter widgets these take account of space ocupied by legends or labels.

The aclock.py and linked_sliders.py demos provide simple examples of this approach.

Use of graphics primitives

See demo primitives.py.

These notes are for those wishing to draw directly to the Screen instance. This is done by providing the user Screen class with an after_open() method which is written to issue the display driver calls.

The following code instantiates two classes:

import hardware_setup  # Create a display instance
from gui.core.ugui import Screen, ssd, display

The ssd object is an instance of the object defined in the display driver. It is a requirement that this is a subclass of framebuf.FrameBuffer. Hence ssd supports all the graphics primitives provided by FrameBuffer. These may be used to draw on the Screen.

The display object has methods with the same names and args as those of ssd. These support greying out. So you can write (for example)

display.rect(10, 10, 50, 50, RED)

To render in the correct colors it is wise ensure that greying out is disabled prior to calling display methods. This is done with

display.usegrey(False)

There is little point in issuing display.rect as it confers no advantage over ssd.rect. However the Display class adds methods not currently available in framebuf. These are listed below.

• circle(self, x0, y0, r, color, width =1) Width specifies the line width.
• fillcircle(self, x0, y0, r, color)
• clip_rect(self, x, y, w, h, color) Rectangle with clipped corners.
• fill_clip_rect(self, x, y, w, h, color)
• print_left(self, writer, x, y, txt, fgcolor=None, bgcolor=None, invert=False)
• print_centred(self, writer, x, y, text, fgcolor=None, bgcolor=None, invert=False)

Hopefully these are self explanatory. The Display methods use the framebuf convention of x, y coordinates rather than the row, col system used by micro-gui.

The primitives.py demo provides a simple example.

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Appendix 2 Freezing bytecode

This achieves a major saving of RAM. The correct way to do this is via a manifest file. The first step is to clone MicroPython and prove that you can build and deploy firmware to the chosen platform. Build instructions vary between ports and can be found in the MicroPython source tree in ports/<port>/README.md.

The following is an example of how the entire GUI with fonts, demos and all widgets can be frozen on RP2.

Build script:

cd /mnt/qnap2/data/Projects/MicroPython/micropython/ports/rp2
MANIFEST='/mnt/qnap2/Scripts/manifests/rp2_manifest.py'

make submodules
make clean
if make -j 8 BOARD=PICO FROZEN_MANIFEST=$MANIFEST
then
    echo Firmware is in build-PICO/firmware.uf2
else
    echo Build failure
fi
cd -

Manifest file contents (first line ensures that the default files are frozen):

include("$(MPY_DIR)/ports/rp2/boards/manifest.py")
freeze('/mnt/qnap2/Scripts/modules/rp2_modules')

The directory /mnt/qnap2/Scripts/modules/rp2_modules contains only a symlink to the gui directory of the micropython-micro-gui source tree. The freezing process follows symlinks and respects directory structures.

It is usually best to keep hardware_setup.py unfrozen for ease of making changes. I also keep the display driver and boolpalette.py in the filesystem as I have experienced problems freezing display drivers - but feel free to experiment.

Appendix 3 Cross compiling

This addresses the case where a memory error occurs on import. There are better savings with frozen bytecode, but cross compiling the main program module saves the compiler from having to compile a large module on the target hardware. The cross compiler is documented here.

Change to the directory gui/core and issue:

$ /path/to/micropython/mpy-cross/mpy-cross ugui.py

This creates a file ugui.mpy. It is necessary to move, delete or rename ugui.py as MicroPython loads a .py file in preference to .mpy.

If "incorrect mpy version" errors occur, the cross compiler should be recompiled.