Question

I am trying to switch my application over to using framebuffer/renderbuffer objects (looking to render to texture later) but whenever I use the framebuffer/renderbuffer, nothing renders. When the default framebuffer is left on, as is the default, it renders fine; All colour, depth and stencil related features work exactly as expected.

Initialisation code:

if(frameBuffer == 0 || !GLES20.glIsFramebuffer(frameBuffer)){
    int[] retVal = new int[1];
    GLES20.glGenFramebuffers(1, retVal, 0);
    frameBuffer = retVal[0];
    retVal[0] = 0;

    if(renderBufferColour != 0 || !GLES20.glIsRenderbuffer(renderBufferColour)){
        GLES20.glGenRenderbuffers(1, retVal, 0);
        renderBufferColour = retVal[0];
    }

    if(renderBufferDepth != 0 || !GLES20.glIsRenderbuffer(renderBufferDepth)){
        GLES20.glGenRenderbuffers(1, retVal, 0);
        renderBufferDepth = retVal[0];
    }

    if(renderBufferStencil != 0 || !GLES20.glIsRenderbuffer(renderBufferStencil)){
        GLES20.glGenRenderbuffers(1, retVal, 0);
        renderBufferStencil = retVal[0];
    }
}

Framebuffer enabling code (commenting this out allows rendering using the default buffer):

GLES20.glBindFramebuffer(GLES20.GL_FRAMEBUFFER, frameBuffer);

GLES20.glBindRenderbuffer(GLES20.GL_RENDERBUFFER, renderBufferColour);
GLES20.glRenderbufferStorage(GLES20.GL_RENDERBUFFER, GLES20.GL_RGBA4, width, height);
GLES20.glFramebufferRenderbuffer(
        GLES20.GL_FRAMEBUFFER,
        GLES20.GL_COLOR_ATTACHMENT0,
        GLES20.GL_RENDERBUFFER,
        renderBufferColour);

GLES20.glBindRenderbuffer(GLES20.GL_RENDERBUFFER, renderBufferDepth);
GLES20.glRenderbufferStorage(GLES20.GL_RENDERBUFFER, GLES20.GL_DEPTH_COMPONENT16, width, height);
GLES20.glFramebufferRenderbuffer(
        GLES20.GL_FRAMEBUFFER,
        GLES20.GL_DEPTH_ATTACHMENT,
        GLES20.GL_RENDERBUFFER,
        renderBufferDepth);

GLES20.glBindRenderbuffer(GLES20.GL_RENDERBUFFER, renderBufferStencil);
GLES20.glRenderbufferStorage(GLES20.GL_RENDERBUFFER, GLES20.GL_STENCIL_INDEX8, width, height);
GLES20.glFramebufferRenderbuffer(
        GLES20.GL_FRAMEBUFFER,
        GLES20.GL_STENCIL_ATTACHMENT,
        GLES20.GL_RENDERBUFFER,
        renderBufferStencil);

if (GLES20.glCheckFramebufferStatus(GLES20.GL_FRAMEBUFFER) != GLES20.GL_FRAMEBUFFER_COMPLETE)
    throw new RuntimeException(String.format("Failed to make complete framebuffer object %x", GLES20.glCheckFramebufferStatus(GLES20.GL_FRAMEBUFFER)));

The exception at the end is not thrown and when checking glGetError() after each step, no error is returned. Am I missing something here?

Answer 1

Ok, after reading the OpenGLES 2.0 manual, I came across this paragraph:

By allowing the images of a renderbuffer to be attached to a framebuffer,
OpenGL ES provides a mechanism to support off-screen rendering. Further, by
allowing the images of a texture to be attached to a framebuffer, OpenGL ES provides
a mechanism to support render to texture.

It appears to me that application render buffers are always off-screen not on-screen as I had expected. This, if I have read correctly, is why there is no image on the screen.