Request a DepthBuffer in OpenGL ES for iPhone - iphone

Question

I'm creating a 3D OpenGL ES view on the iPhone and want to set up a depth buffer, so I can use it. I'm calling glEnable(GL_DEPTH_TEST) and such, but because I haven't set up the z-buffer, it does nothing.
I'm looking for an equivalent call to
glutInitDisplayMode(GLUT_DEPTH)
Any help would be most welcome. Thanks!

Answer 1

As you suspect, you've no depth buffer. You'll need to attach a depth buffer to your frame buffer in whatever UIView subclass you've created that uses a CAEAGLLayer as its layer.
Supposing you're working with Apple's OpenGL ES Xcode template, the relevant UIView subclass is EAGLView. There's a method in there, createFramebuffer, that is responsible for creating the frame buffer. Initially it'll say:
- (void)createFramebuffer
{
if (context && !defaultFramebuffer)
{
[EAGLContext setCurrentContext:context];
// Create default framebuffer object.
glGenFramebuffers(1, &defaultFramebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, defaultFramebuffer);
// Create color render buffer and allocate backing store.
glGenRenderbuffers(1, &colorRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);
[context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer *)self.layer];
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &framebufferWidth);
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &framebufferHeight);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, colorRenderbuffer);
if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
NSLog(#"Failed to make complete framebuffer object %x", glCheckFramebufferStatus(GL_FRAMEBUFFER));
}
}
What that does is generates and binds a frame buffer, then it generates and binds a colour render buffer, gifts the colour buffer the inherent storage that comes with a CAEAGLLayer, grabs the frame dimensions for later and attaches the colour buffer to the render buffer.
You need also to create and attach a depth buffer. Which should be as simple as (with a suitable instance variable added for depthRenderbuffer; typing directly in here):
glGenRenderbuffers(1, &depthRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, framebufferWidth, framebufferHeight);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderbuffer);
Which does what it looks like it does — generates and binds a render buffer, allocates it storage to be a 16bit depth buffer of the same dimensions as the colour buffer and then attaches it to the frame buffer.
So, in total (untested):
- (void)createFramebuffer
{
if (context && !defaultFramebuffer)
{
[EAGLContext setCurrentContext:context];
// Create default framebuffer object.
glGenFramebuffers(1, &defaultFramebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, defaultFramebuffer);
// Create color render buffer and allocate backing store.
glGenRenderbuffers(1, &colorRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, colorRenderbuffer);
[context renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer *)self.layer];
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &framebufferWidth);
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &framebufferHeight);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, colorRenderbuffer);
// Create depth render buffer and allocate backing store.
glGenRenderbuffers(1, &depthRenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, depthRenderbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, framebufferWidth, framebufferHeight);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthRenderbuffer);
if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
NSLog(#"Failed to make complete framebuffer object %x", glCheckFramebufferStatus(GL_FRAMEBUFFER));
}
}