GLFM

GLFM is a C API for mobile app development with OpenGL ES. It is largely inspired by GLFW.

GLFM runs on iOS 9, tvOS 9, Android 4.1 (API 16), and WebGL 1.0 (via Emscripten).

Additionally, GLFM provides Metal support on iOS and tvOS.

Features

• OpenGL ES 2, OpenGL ES 3, and Metal display setup.
• Retina / high-DPI support.
• Touch and keyboard events.
• Accelerometer, magnetometer, gyroscope, and device rotation (iOS/Android only)
• Events for application state and context loss.

Feature Matrix

Additionally, there is prelimnary support for macOS with OpenGL 3.2. The macOS version is useful for development purposes, but is not release quality. There is no function to set the window size, for example.

Non-goals

GLFM is limited in scope, and isn't designed to provide everything needed for an app. For example, GLFM doesn't provide (and will never provide) the following:

• No image loading.
• No text rendering.
• No audio.
• No menus, UI toolkit, or scene graph.
• No integration with other mobile features like web views, maps, or game scores.

Instead, GLFM can be used with other cross-platform libraries that provide what an app needs.

Use GLFM

A CMakeLists.txt file is provided for convenience, although CMake is not required.

Without CMake:

1. Add the GLFM source files (in include and src) to your project.
2. Include a void glfmMain(GLFMDisplay *display) function in a C/C++ file.

For release builds, define NDEBUG to remove superfluous logging statements. NDEBUG is automatically defined for release builds in Android Studio, but not in Xcode.

Example

This example initializes the display in glfmMain() and draws a triangle in onDraw(). A more detailed example is available here.

#include "glfm.h"

static GLint program = 0;
static GLuint vertexBuffer = 0;
static GLuint vertexArray = 0;

static void onDraw(GLFMDisplay *display);
static void onSurfaceDestroyed(GLFMDisplay *display);

void glfmMain(GLFMDisplay *display) {
    glfmSetDisplayConfig(display,
                         GLFMRenderingAPIOpenGLES2,
                         GLFMColorFormatRGBA8888,
                         GLFMDepthFormatNone,
                         GLFMStencilFormatNone,
                         GLFMMultisampleNone);
    glfmSetRenderFunc(display, onDraw);
    glfmSetSurfaceDestroyedFunc(display, onSurfaceDestroyed);
}

static void onSurfaceDestroyed(GLFMDisplay *display) {
    // When the surface is destroyed, all existing GL resources are no longer valid.
    program = 0;
    vertexBuffer = 0;
    vertexArray = 0;
}

static GLuint compileShader(const GLenum type, const GLchar *shaderString, GLint shaderLength) {
    GLuint shader = glCreateShader(type);
    glShaderSource(shader, 1, &shaderString, &shaderLength);
    glCompileShader(shader);
    return shader;
}

static void onDraw(GLFMDisplay *display) {
    if (program == 0) {
        const GLchar vertexShader[] =
            "#version 100\n"
            "attribute highp vec4 position;\n"
            "void main() {\n"
            "   gl_Position = position;\n"
            "}";

        const GLchar fragmentShader[] =
            "#version 100\n"
            "void main() {\n"
            "  gl_FragColor = vec4(0.85, 0.80, 0.75, 1.0);\n"
            "}";

        program = glCreateProgram();
        GLuint vertShader = compileShader(GL_VERTEX_SHADER, vertexShader, sizeof(vertexShader) - 1);
        GLuint fragShader = compileShader(GL_FRAGMENT_SHADER, fragmentShader, sizeof(fragmentShader) - 1);

        glAttachShader(program, vertShader);
        glAttachShader(program, fragShader);

        glLinkProgram(program);

        glDeleteShader(vertShader);
        glDeleteShader(fragShader);
    }
    if (vertexBuffer == 0) {
        const GLfloat vertices[] = {
             0.0,  0.5, 0.0,
            -0.5, -0.5, 0.0,
             0.5, -0.5, 0.0,
        };
        glGenBuffers(1, &vertexBuffer);
        glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
        glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
    }

    int width, height;
    glfmGetDisplaySize(display, &width, &height);
    glViewport(0, 0, width, height);
    glClearColor(0.08f, 0.07f, 0.07f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

#if defined(GL_VERSION_3_0) && GL_VERSION_3_0
    if (vertexArray == 0) {
        glGenVertexArrays(1, &vertexArray);
    }
    glBindVertexArray(vertexArray);
#endif

    glUseProgram(program);
    glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);

    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
    glDrawArrays(GL_TRIANGLES, 0, 3);

    glfmSwapBuffers(display);
}

API

See glfm.h

Build the GLFM examples with Xcode

Use cmake to generate an Xcode project:

cmake -D GLFM_BUILD_EXAMPLES=ON -B build/apple -G Xcode 
open build/apple/GLFM.xcodeproj

In Xcode, switch to the glfm_touch target and run on a simulator or a device.

Build the GLFM examples with Emscripten

Use emcmake to set environmental variables for cmake, then build:

emcmake cmake -D GLFM_BUILD_EXAMPLES=ON -B build/emscripten
cmake --build build/emscripten

Then run locally:

emrun build/emscripten/examples/glfm_touch.html

Build the GLFM examples with Android Studio

There is no CMake generator for Android Studio projects, but you can include CMakeLists.txt in a new or existing project.

1. Select "Start a new Android Studio project".
2. Select "No Activity".
3. In "Save location", enter [path/to/glfm]/build/android and press "Finish".
4. In AndroidManifest.xml, add the main <activity> like so:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android">

    <uses-feature android:glEsVersion="0x00020000" android:required="true" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true">

        <!-- Add this activity to your AndroidManifest.xml -->
        <activity android:name="android.app.NativeActivity"
                  android:exported="true"
                  android:configChanges="orientation|screenLayout|screenSize|keyboardHidden|keyboard">
            <meta-data
                android:name="android.app.lib_name"
                android:value="glfm_touch" />  <!-- glfm_triangle, glfm_touch, glfm_typing, glfm_compass, or glfm_test_pattern -->
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>
    </application>

</manifest>

5. In app/build.gradle, add the externalNativeBuild and sourceSets.main sections like so:

apply plugin: 'com.android.application'

android {
    compileSdkVersion 32
    buildToolsVersion "32.0.0"
    defaultConfig {
        applicationId "com.brackeen.glfmexample"
        minSdkVersion 15
        targetSdkVersion 32
        versionCode 1
        versionName "1.0"

        // Add externalNativeBuild in defaultConfig (1/2)
        externalNativeBuild {
            cmake {
                arguments "-DGLFM_BUILD_EXAMPLES=ON"
            }
        }
    }
    
    // Add sourceSets.main and externalNativeBuild (2/2)
    sourceSets.main {
        assets.srcDirs = ["../../../examples/assets"]
    }
    externalNativeBuild {
        cmake {
            path "../../../CMakeLists.txt"
        }
    }
    namespace 'com.brackeen.glfmexample'
}

6. Press "Sync Now" and "Run 'app'"

Caveats

• OpenGL ES 3.1 and 3.2 support is only available in Android.
• GLFM is not thread-safe. All GLFM functions must be called on the main thread (that is, from glfmMain or from the callback functions).

Questions

What IDE should I use? Why is there no desktop implementation? Use Xcode or Android Studio. For desktop, use GLFW with the IDE of your choice.

If you prefer not using the mobile simulators for everyday development, a good solution is to use GLFW instead, and then later port your app to GLFM. Not all OpenGL calls will port to OpenGL ES perfectly, but for maximum OpenGL portability, use OpenGL 3.2 Core Profile on desktop and OpenGL ES 2.0 on mobile.

Why is the entry point glfmMain() and not main()?

Otherwise, it wouldn't work on iOS. To initialize the Objective-C environment, the main() function must create an autorelease pool and call the UIApplicationMain() function, which never returns. On iOS, GLFM doesn't call glfmMain() until after the UIApplicationDelegate and UIViewController are initialized.

Why is GLFM event-driven? Why does GLFM take over the main loop?

Otherwise, it wouldn't work on iOS (see above) or on HTML5, which is event-driven.