How can I test if my framebuffer object is rendering properly?

Question

I'm using a framebuffer object with a color buffer attachment to do some per-pixel hit testing. I'd like to render it to the screen for debugging and testing but right now all I'm getting is a big white nothingness. I assume I have to send some render command similar to glSwapBuffers(), but as I'm only using one buffer I don't know what it would be swapping to. Is there an equivalent command for using just one buffer?

Here's my setup:

 // Store the real framebuffer
 glGetIntegerv(GL_FRAMEBUFFER_BINDING_OES, (GLint*) &regularFbo);
 // Generate an offscreen framebuffer/renderbuffer for rendering the hit detection polys
 // Create framebuffer
 glGenFramebuffersOES(1, &hitDetectionFbo);
 glBindFramebufferOES(GL_FRAMEBUFFER_OES, hitDetectionFbo);
 // Create colorbuffer
 glGenRenderbuffersOES(1, &colorBuffer);
 glBindRenderbufferOES(GL_RENDERBUFFER_OES, colorBuffer);
 // Create storage (RGBA) for color buffer
 glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_RGBA8_OES, SCREEN_WIDTH, SCREEN_HEIGHT);
 // Attach color buffer to framebuffer
 glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, colorBuffer);
 glDisable(GL_DEPTH_TEST);
 glDepthMask(GL_FALSE);

This doesn't flag any glErrors but I'm clearly missing something, as nothing is appearing on screen after I switch over to my new FBO. The program will render just fine if I continue to use the original framebuffer (through a glBindFramebufferOES(GL_FRAMEBUFFER_OES, regularFbo) call).

Thanks for the help, -S

Answer 1

On the iPhone platform, the only FBO that can be used directly as the backbuffer is the one that has a color buffer that has been allocated using:

[myEaglContext renderbufferStorage:GL_RENDERBUFFER fromDrawable: eaglLayer];

If you allocate a color buffer using glRenderbufferStorageOES, then it's a normal off-screen FBO, and the best way to make it show up the screen is to bind it to a texture and render a quad.