setting a CAEAGLLayer properties for OpenGL ES?

Question

Using frame buffer objects for rendering on iOS, which appears to be Apples preferred way of rendering on iOS according to the OpenGL ES Programming Guide for iOS from Apple, one is supposed to use glRenderbufferStorage() for specifying properties like width and hight according to OpenGL ES 2.0 Programming Guide from Munshi, Ginsburg and Shreiner. Apple replaces this with renderbufferStorage:fromDrawable: message sent to the EAGLContext in above guide.

Apple then goes on writing to fetch width and hight from the Renderbuffer as that buffer sets them on creation without further detail.

The width and height are 0 though.

The CAEAGLLayer Class Reference writes to "Set the layer bounds to match the dimensions of the display". The CAEAGLLayer class is the class Apple wants one to use as the backing class of the view one uses. This is done by returning it from the views layerClass method. This CAEAGLLayer only has 1 property "drawableProperties" which is an NSDictionary. Unfortunately that documentation is sparse. Dimensions cannot be set.

Thus: how to go on setting a CAEAGLLayer properties for OpenGL ES?

Here's my code thus far (Note an old example of Apple uses initWithCoder, I either guessed or got from somewhere I don't remember to use initWithFrame):

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) 
    {
        // Initialization code
        theCAEAGLLayer = (CAEAGLLayer*)self.layer;
        theCAEAGLLayer.opaque = YES;
        theEAGLContext = [[EAGLContext alloc] initWithAPI:kEAGLRenderingAPIOpenGLES2];
        [EAGLContext setCurrentContext:theEAGLContext];
        glGenFramebuffers(1, &theFramebuffer);
        glBindFramebuffer(GL_FRAMEBUFFER, theFramebuffer);
        glGenRenderbuffers(1, &theColorRenderbuffer);
        glBindRenderbuffer(GL_RENDERBUFFER, theColorRenderbuffer);
        [theEAGLContext renderbufferStorage:GL_RENDERBUFFER fromDrawable:theCAEAGLLayer];
        glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, theColorRenderbuffer);
        glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &widthOfTheColorRenderbuffer);
        glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &heightOfTheColorRenderbuffer);
        glGenRenderbuffers(1, &theDepthRenderbuffer);
        glBindRenderbuffer(GL_RENDERBUFFER, theDepthRenderbuffer);
        glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, widthOfTheColorRenderbuffer, heightOfTheColorRenderbuffer);
        glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, theDepthRenderbuffer);
        if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
        {

        }
    }
    return self;
}

Answer 1

Proper answer:

UIKit batches together certain operations and defers them until later in the runloop. That's because you may have code that changes the size of a view and changes different bits of text inside it. You probably want that stuff to happen atomically.

What that probably means for you is that the layer hasn't been sized yet. Have you tried moving what you have to - (void)layoutSubviews ?

If you're planning to target iOS 5 only, you can just use GLKView and avoid writing any of this stuff for yourself.

Other comments:

glRenderbufferStorage would create storage at an opaque location that OpenGL could draw to, but how should the OS guess which of your frame buffers is the one you want to show to the user, rather than merely being an intermediate result? The OpenGL spec explicitly doesn't define how you communicate that to your specific OS. In iOS it's achieved via renderbufferStorage:fromDrawable: — that says to add storage that equates to the CALayer that iOS knows how to composite. Apple's method is not a replacement for glRenderbufferStorage , it does something that glRenderbufferStorage can't and shouldn't, and there are many times you'll use it instead even when programming for iOS only.

- (id)initWithFrame: is the initialiser you'd use if you were creating the view manually. - (id)initWithCoder: is used by the system to load the view from a NIB.

Has your UIView definitely specified its layerClass as CAEAGLLayer ? If not then the call to your EAGL context would be permitted to fail.