Multisampled render to texture in ios - iphone

Question

I am attempting to render to a texture in ios with multisampling enabled and then use that texture in my final output. Is this possible?
So far I have only gotten black textures or aliased images. The code I am using is:
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA4, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glGenFramebuffers(1, &framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
glGenRenderbuffers(1, &colorRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);
//glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA8_OES, width, height);
glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER, 4, GL_RGBA4, width, height);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, colorRenderbuffer);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);
glGenRenderbuffers(1, &depthRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
//glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, width, self.view.bounds.size.height);
glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER, 4, GL_DEPTH_COMPONENT16, width, height);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderbuffer);
GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER) ;
if(status != GL_FRAMEBUFFER_COMPLETE) {
NSLog(#"failed to make complete framebuffer object %x", status);
}
// Render my scene
glBindFramebuffer( GL_FRAMEBUFFER, framebuffer );
glViewport(0,0,width,height);
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
// Draw scene
// Then bind default framebuffer
glBindFramebuffer( GL_FRAMEBUFFER, 1 );
// Draw other things
// Now resolve the multisampling and draw texture
glResolveMultisampleFramebufferAPPLE();
glUseTexture( GL_TEXTURE_2D, texture );
// Draw with texture
This code does not work. It fails if I make the depth render buffer multisampled. If I just use a normal fbo for the depth then it works, but produces an aliased image.
Anyone know where I am going wrong?
Thanks!

Answer 1

Yes! I found what I was doing wrong. I wrongly thought that I could have the following:
Framebuffer
Multisampled colour render buffer attached to a texture
Multisampled depth buffer
But you cannot do this. D: You have to have the following:
Multisampled framebuffer:
Multisampled colour render buffer (Not attached to a texture)
Multisampled depth render buffer
Normal framebuffer:
Colour render buffer attached to a texture. This is what will be written to by glResolveMultisampleFramebufferAPPLE() and what we will use to render the result.
No depth buffer.
I.e. you have to copy the results of the multisampled render to a whole new framebuffer.
Some code:
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA4, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glGenFramebuffers(1, &resolved_framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, resolved_framebuffer);
glGenRenderbuffers(1, &resolvedColorRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, resolvedColorRenderbuffer);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, texture, 0);
glGenFramebuffers(1, &framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);
glGenRenderbuffers(1, &colorRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);
glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER, 4, GL_RGBA8_OES, width, height);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, colorRenderbuffer);
glGenRenderbuffers(1, &depthRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER, 4, GL_DEPTH_COMPONENT16, width, height);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderbuffer);
GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER) ;
if(status != GL_FRAMEBUFFER_COMPLETE) {
NSLog(#"failed to make complete framebuffer object %x", status);
}
// Render my scene
glBindFramebuffer( GL_FRAMEBUFFER, framebuffer );
glViewport(0,0,width,height);
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
// Draw scene
// Then bind default framebuffer
glBindFramebuffer( GL_FRAMEBUFFER, 1 );
// Draw other things
// Now resolve the multisampling into the other fbo
glBindFramebuffer( GL_READ_FRAMEBUFFER_APPLE, framebuffer );
glBindFramebuffer( GL_DRAW_FRAMEBUFFER_APPLE, resolved_framebuffer );
glResolveMultisampleFramebufferAPPLE();
glBindTexture( GL_TEXTURE_2D, texture );
// Draw with texture
Thanks Goz, you got me in the right direction!

Answer 2

I assume you've been working from the sample on this page?
Remove the glFramebufferTexture2D call as this may be causing the multisample render buffer to detach and hence you are have a multisampled back buffer and a single sampled render buffer. Furthermore, creating a single sampled depth buffer wil solve your issues as it will not be paired with theat single sampled render buffer.
Edit: When do you get the error? On the one creating the render buffer? If so you may be best off trying it exactly as in the link I posted (which I assume you are working for).
ie.
glRenderbufferStorageMultisampleAPPLE(GL_RENDERBUFFER, 4, GL_RGBA8_OES, width, height);