Android OpenGL ES Framebuffer objects - rendering depth-buffer to texture

Question

I am using an Android device running Froyo supporting OpenGL ES 1.1 and OpenGL ES 2.0

I want to render the depth buffer to a texture. Having seen a number of example

Answer 1

OK, an answer of sorts. Got this to work on Android 2.2 with OpenGL ES 2:

    // Create a frame buffer
    glGenFramebuffers( 1, &(frame_buffer ) );

    // Generate a texture to hold the colour buffer
    glGenTextures(1, &(colour_texture) );
    glBindTexture(GL_TEXTURE_2D, colour_texture);
    // Width and height do not have to be a power of two
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA,
            pixelWidth, pixelHeight,
            0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

    // Probably just paranoia
    glBindTexture(GL_TEXTURE_2D, 0);

    // Create a texture to hold the depth buffer
    glGenTextures(1, &(depth_texture) );
    glBindTexture(GL_TEXTURE_2D, depth_texture);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT,
            pixelWidth, pixelHeight,
            0, GL_DEPTH_COMPONENT, GL_UNSIGNED_SHORT, NULL);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

    glBindTexture(GL_TEXTURE_2D, 0);        

    glBindFramebuffer(GL_FRAMEBUFFER, frame_buffer);

    // Associate the textures with the FBO.

    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                    GL_TEXTURE_2D, colour_texture, 0);

    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT,
                    GL_TEXTURE_2D, depth_texture, 0);

    // Check FBO status.    
    GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);

    if ( status == GL_FRAMEBUFFER_COMPLETE )
    {
        // Success
    }

Pretty trivial really, follow the OpenGL ES2 manual and do everything in the right order.

Tried this with OpenGL ES 1.1, adding OES to the required function calls and _OES to the constants since frame buffer objects is an extension. Any attempt to attach a depth texture to the frame buffer results in an incomplete frame buffer object.

So at the moment my conclusion is that this doesn't work with OpenGL ES 1.1 on Android, but it clearly does work with ES 2.2.

If anyone has a solution for ES 1.1 it would be interesting to see it.

Answer 2

Rendering to a depth texture isn't supported on many devices. You'll need to attach a renderbuffer for your depth buffer.