// for EGL calls
#define EGL_EGLEXT_PROTOTYPES
#include "EGL/egl.h"
#include "EGL/eglext.h"
#include "GLES/gl.h"
#define GL_GLEXT_PROTOTYPES
#include "GLES/glext.h"

// Use code from this repository. Note that define __ANDROID_API__ must be set properly for it to work
// Also add -lEGL at link stage
#include "GraphicBuffer.h" 

// bind FBO (create FBO my_handle first!)
glBindFramebuffer(GL_FRAMEBUFFER, my_handle);

// attach texture to FBO (create texture my_texture first!)
glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, my_texture, 0);

// usage for the GraphicBuffer
int usage = GraphicBuffer::USAGE_HW_RENDER | GraphicBuffer::USAGE_SW_READ_OFTEN | GraphicBuffer::USAGE_SW_WRITE_NEVER;

// create GraphicBuffer
GraphicBuffer* graphicBuf = new GraphicBuffer(width, height, PIXEL_FORMAT_RGBA_8888, usage);

// get the native buffer
auto clientBuf = (EGLClientBuffer) graphicBuf->getNativeBuffer();

// obtaining the EGL display
EGLDisplay disp = eglGetDisplay(EGL_DEFAULT_DISPLAY);

// specifying the image attributes
EGLint eglImageAttributes[] = {EGL_IMAGE_PRESERVED_KHR, EGL_TRUE, EGL_NONE};

// creating an EGL image
EGLImageKHR imageEGL = eglCreateImageKHR(disp, EGL_NO_CONTEXT, EGL_NATIVE_BUFFER_ANDROID, clientBuf, eglImageAttributes);

// Doing some OpenGL rendering like glDrawArrays
// Shaders also work, need `#extension GL_OES_EGL_image_external : require`
// Now the result is inside the FBO my_handle

// binding the OUTPUT texture
glBindTexture(GL_TEXTURE_2D, my_texture);

// attaching an EGLImage to OUTPUT texture
glEGLImageTargetTexture2DOES(GL_TEXTURE_2D, imageEGL);

// Obtaining the content image:

// pointer for reading and writing texture data
void *readPtr, *writePtr;

// locking the buffer
graphicBuf->lock(GraphicBuffer::USAGE_SW_READ_OFTEN, &readPtr);

// setting the write pointer
writePtr = <set to a valid memory area, like malloc(_YOUR_SIZE_)>

// obtaining the stride (for me it was always = width)
int stride = graphicBuf->getStride();

// loop over texture rows
for (int row = 0; row < height; row++) {
    // copying, 4 = 4 channels RGBA because of the format above
    memcpy(writePtr, readPtr, width * 4);

    // adding stride * 4 to read pointer
    readPtr = (void *)(int(readPtr) + stride * 4);

    // adding width * 4 to write pointer
    writePtr = (void *)(int(writePtr) + width * 4);
}

// NOW data is in writePtr memory

// unlocking the buffer
graphicBuf->unlock();

// for EGL calls
#define EGL_EGLEXT_PROTOTYPES
#include "EGL/egl.h"
#include "EGL/eglext.h"
#include "GLES/gl.h"
#define GL_GLEXT_PROTOTYPES
#include "GLES/glext.h"

// for API >= 26
// Also add -lEGL -lnativewindow -lGLESv3 at link stage
#include "android/hardware_buffer.h"

// bind FBO (create FBO my_handle first!)
glBindFramebuffer(GL_FRAMEBUFFER, my_handle);

// attach texture to FBO (create texture my_texture first!)
glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, my_texture, 0);

// OUR parameters that we will set and give it to AHardwareBuffer
AHardwareBuffer_Desc usage;

// filling in the usage for HardwareBuffer
usage.format = AHARDWAREBUFFER_FORMAT_R8G8B8A8_UNORM;
usage.height = outputHeight;
usage.width = outputWidth;
usage.layers = 1;
usage.rfu0 = 0;
usage.rfu1 = 0;
usage.stride = 10;
usage.usage = AHARDWAREBUFFER_USAGE_CPU_READ_OFTEN | AHARDWAREBUFFER_USAGE_CPU_WRITE_NEVER
        | AHARDWAREBUFFER_USAGE_GPU_COLOR_OUTPUT;

// create GraphicBuffer
AHardwareBuffer* graphicBuf;
AHardwareBuffer_allocate(&usage, &graphicBuf); // it's worth to check the return code

// ACTUAL parameters of the AHardwareBuffer which it reports
AHardwareBuffer_Desc usage1;

// for stride, see below
AHardwareBuffer_describe(graphicBuf, &usage1);

// get the native buffer
EGLClientBuffer clientBuf = eglGetNativeClientBufferANDROID(graphicBuf);

// obtaining the EGL display
EGLDisplay disp = eglGetDisplay(EGL_DEFAULT_DISPLAY);

// specifying the image attributes
EGLint eglImageAttributes[] = {EGL_IMAGE_PRESERVED_KHR, EGL_TRUE, EGL_NONE};

// creating an EGL image
EGLImageKHR imageEGL = eglCreateImageKHR(disp, EGL_NO_CONTEXT, EGL_NATIVE_BUFFER_ANDROID, clientBuf, eglImageAttributes);
/**
 * @note this part should be earlies than any draw or framebuffer options.
 * @note refer to answer of @solidpixel at https://stackoverflow.com/questions/64447069/use-gleglimagetargettexture2does-to-replace-glreadpixels-on-android
 * @{
 */
// binding the OUTPUT texture
gl->glBindTexture(GL_TEXTURE_2D, my_texture);

// attaching an EGLImage to OUTPUT texture
glEGLImageTargetTexture2DOES(GL_TEXTURE_2D, imageEGL);
/**
 * @}
 */
// Doing some OpenGL rendering like glDrawArrays
// Shaders also work, need `#extension GL_OES_EGL_image_external_essl3 : require`
// Now the result is inside the FBO my_handle

// Obtaining the content image:

// pointer for reading and writing texture data
void *readPtr, *writePtr;
/**
 * @note We must make sure all drawing options finished before read back.
 * @{
 */
 glFinish();
 /**
 * @}
 */
// locking the buffer
AHardwareBuffer_lock(graphicBuf, AHARDWAREBUFFER_USAGE_CPU_READ_OFTEN, -1, nullptr, (void**) &readPtr); // worth checking return code

// setting the write pointer
writePtr = <set to a valid memory area, like malloc(_YOUR_SIZE_)>

// obtaining the stride (for me it was always = width)
int stride = usage1.stride;

// loop over texture rows
for (int row = 0; row < height; row++) {
    // copying, 4 = 4 channels RGBA because of the format above
    memcpy(writePtr, readPtr, width * 4);

    // adding stride * 4 to read pointer
    readPtr = (void *)(int(readPtr) + stride * 4);

    // adding width * 4 to write pointer
    writePtr = (void *)(int(writePtr) + width * 4);
}

// NOW data is in writePtr memory

// unlocking the buffer
AHardwareBuffer_unlock(graphicBuf, nullptr); // worth checking return code