Android initialise openGL2.0 context with EGL

Question

I want to do off-screen image processing on Android in native code, so I need create the openGL context in native code by EGL.

By EGL, we can create EGLSurface, I can see there are three choices there: * EGL_WINDOW_BIT * EGL_PIXMAP_BIT * EGL_BUFFER_BIT

The first one is for on-screen processing, the second one is for off-screen, so I use EGL_PIXMAP_BIT like this:

// Step 1 - Get the default display.
EGLDisplay eglDisplay = eglGetDisplay((EGLNativeDisplayType) 0);
if ((eglDisplay = eglGetDisplay(EGL_DEFAULT_DISPLAY)) == EGL_NO_DISPLAY) {
    LOGH("eglGetDisplay() returned error %d", eglGetError());
    exit(-1);
}

// Step 2 - Initialize EGL.
if (!eglInitialize(eglDisplay, 0, 0)) {
    LOGH("eglInitialize() returned error %d", eglGetError());
    exit(-1);
}

// Step 3 - Make OpenGL ES the current API.
eglBindAPI(EGL_OPENGL_ES_API);

// Step 4 - Specify the required configuration attributes.
EGLint pi32ConfigAttribs[] = { EGL_SURFACE_TYPE, EGL_PIXMAP_BIT,
        EGL_BLUE_SIZE, 8, EGL_GREEN_SIZE, 8, EGL_RED_SIZE, 8, EGL_NONE,
        EGL_BIND_TO_TEXTURE_RGBA, EGL_TRUE };

// Step 5 - Find a config that matches all requirements.
int iConfigs;
EGLConfig eglConfig;
eglChooseConfig(eglDisplay, pi32ConfigAttribs, &eglConfig, 1, &iConfigs);
if (iConfigs != 1) {
    LOGH(
            "Error: eglChooseConfig(): config not found %d - %d.\n", eglGetError(), iConfigs);
    exit(-1);
}

// Step 6 - Create a surface to draw to.
EGLSurface eglSurface = eglCreatePbufferSurface(eglDisplay, eglConfig,
        NULL);

// Step 7 - Create a context.
EGLContext eglContext = eglCreateContext(eglDisplay, eglConfig, NULL,
        ai32ContextAttribs);

// Step 8 - Bind the context to the current thread
eglMakeCurrent(eglDisplay, eglSurface, eglSurface, eglContext);

The code failed at step 5, it seems Android doesn't support off screen processing? EGL_PIXMAP_BIT type is not supported.!

Answer 1

You are trying to use EGL options that just don't work on Android and pbuffers only work on some GPUs - not Nvidia Tegra. pi32ConfigAttribs[] should look like this regardless of whether it will be on-screen or off-screen:

EGLint pi32ConfigAttribs[] = 
{
    EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
    EGL_RED_SIZE, 8,
    EGL_GREEN_SIZE, 8,
    EGL_BLUE_SIZE, 8,
    EGL_ALPHA_SIZE, 8,
    EGL_DEPTH_SIZE, 0,
    EGL_STENCIL_SIZE, 0,
    EGL_NONE
};

Android is very inflexible in how they support off-screen EGLSurfaces. They defined their own pixmap type named EGL_NATIVE_BUFFER_ANDROID.

To create an EGL surface that is off-screen on Android, construct a SurfaceTexture and pass that to eglCreateWindowSurface(). You should also look at using the EGL Image Extension and EGL_NATIVE_BUFFER_ANDROID, as discussed here:

http://software.intel.com/en-us/articles/using-opengl-es-to-accelerate-apps-with-legacy-2d-guis

http://software.intel.com/en-us/articles/porting-opengl-games-to-android-on-intel-atom-processors-part-1

UPDATE: Here is some sample code that creates an off-screen surface:

private EGL10 mEgl;
private EGLConfig[] maEGLconfigs;
private EGLDisplay mEglDisplay = null;
private EGLContext mEglContext = null;
private EGLSurface mEglSurface = null;
private EGLSurface[] maEglSurfaces = new EGLSurface[MAX_SURFACES];

@Override
public void onSurfaceTextureAvailable(SurfaceTexture surfaceTexture, int width, int height) 
{
    InitializeEGL();
    CreateSurfaceEGL(surfaceTexture, width, height);
}

private void InitializeEGL()
{
    mEgl = (EGL10)EGLContext.getEGL();

    mEglDisplay = mEgl.eglGetDisplay(EGL10.EGL_DEFAULT_DISPLAY);

    if (mEglDisplay == EGL10.EGL_NO_DISPLAY)
        throw new RuntimeException("Error: eglGetDisplay() Failed " + GLUtils.getEGLErrorString(mEgl.eglGetError()));

    int[] version = new int[2];

    if (!mEgl.eglInitialize(mEglDisplay, version))
        throw new RuntimeException("Error: eglInitialize() Failed " + GLUtils.getEGLErrorString(mEgl.eglGetError()));

    maEGLconfigs = new EGLConfig[1];

    int[] configsCount = new int[1];
    int[] configSpec = new int[]
    {
        EGL10.EGL_RENDERABLE_TYPE, EGL_OPENGL_ES2_BIT,
        EGL10.EGL_RED_SIZE, 8,
        EGL10.EGL_GREEN_SIZE, 8,
        EGL10.EGL_BLUE_SIZE, 8,
        EGL10.EGL_ALPHA_SIZE, 8,
        EGL10.EGL_DEPTH_SIZE, 0,
        EGL10.EGL_STENCIL_SIZE, 0,
        EGL10.EGL_NONE
    };
    if ((!mEgl.eglChooseConfig(mEglDisplay, configSpec, maEGLconfigs, 1, configsCount)) || (configsCount[0] == 0))
        throw new IllegalArgumentException("Error: eglChooseConfig() Failed " + GLUtils.getEGLErrorString(mEgl.eglGetError()));

    if (maEGLconfigs[0] == null)
        throw new RuntimeException("Error: eglConfig() not Initialized");

    int[] attrib_list = { EGL_CONTEXT_CLIENT_VERSION, 2, EGL10.EGL_NONE };

    mEglContext = mEgl.eglCreateContext(mEglDisplay, maEGLconfigs[0], EGL10.EGL_NO_CONTEXT, attrib_list);  
}

private void CreateSurfaceEGL(SurfaceTexture surfaceTexture, int width, int height)
{
    surfaceTexture.setDefaultBufferSize(width, height);

    mEglSurface = mEgl.eglCreateWindowSurface(mEglDisplay, maEGLconfigs[0], surfaceTexture, null);

    if (mEglSurface == null || mEglSurface == EGL10.EGL_NO_SURFACE)
    {
        int error = mEgl.eglGetError();

        if (error == EGL10.EGL_BAD_NATIVE_WINDOW)
        {
            Log.e(LOG_TAG, "Error: createWindowSurface() Returned EGL_BAD_NATIVE_WINDOW.");
            return;
        }
        throw new RuntimeException("Error: createWindowSurface() Failed " + GLUtils.getEGLErrorString(error));
    }
    if (!mEgl.eglMakeCurrent(mEglDisplay, mEglSurface, mEglSurface, mEglContext))
        throw new RuntimeException("Error: eglMakeCurrent() Failed " + GLUtils.getEGLErrorString(mEgl.eglGetError()));

    int[] widthResult = new int[1];
    int[] heightResult = new int[1];

    mEgl.eglQuerySurface(mEglDisplay, mEglSurface, EGL10.EGL_WIDTH, widthResult);
    mEgl.eglQuerySurface(mEglDisplay, mEglSurface, EGL10.EGL_HEIGHT, heightResult);
    Log.i(LOG_TAG, "EGL Surface Dimensions:" + widthResult[0] + " " + heightResult[0]);
}

private void DeleteSurfaceEGL(EGLSurface eglSurface)
{
    if (eglSurface != EGL10.EGL_NO_SURFACE)
        mEgl.eglDestroySurface(mEglDisplay, eglSurface);
}