Using Core OpenGL to programmatically create a context with depth buffer: What am I doing wrong? - objective-c

Question

I'm trying to create an OpenGL context with depth buffer using Core OpenGl. I then wish to display the OpenGL content via a CAOpenGLLayer. From what I've read it seems I should be able to create the desired context by the following method:
I declare the following instance variable in the interface
#interface TorusCAOpenGLLayer : CAOpenGLLayer
{
//omitted code
CGLPixelFormatObj pix;
GLint pixn;
CGLContextObj ctx;
}
Then in the implementation I override copyCGLContextForPixelFormat, which I believe should create the required context
- (CGLContextObj)copyCGLContextForPixelFormat:(CGLPixelFormatObj)pixelFormat
{
CGLPixelFormatAttribute attrs[] =
{
kCGLPFAColorSize, (CGLPixelFormatAttribute)24,
kCGLPFAAlphaSize, (CGLPixelFormatAttribute)8,
kCGLPFADepthSize, (CGLPixelFormatAttribute)24,
(CGLPixelFormatAttribute)0
};
NSLog(#"Pixel format error:%d", CGLChoosePixelFormat(attrs, &pix, &pixn)); //returns 0
NSLog(#"Context error: %d", CGLCreateContext(pix, NULL, &ctx)); //returns 0
NSLog(#"The context:%p", ctx); // returns same memory address as similar NSLog call in function below
return ctx;
}
Finally I override drawInCGLContext to display the content.
-(void)drawInCGLContext:(CGLContextObj)glContext pixelFormat: (CGLPixelFormatObj)pixelFormat forLayerTime:(CFTimeInterval)timeInterval displayTime:(const CVTimeStamp *)timeStamp
{
// Set the current context to the one given to us.
CGLSetCurrentContext(glContext);
int depth;
NSLog(#"The context again:%p", glContext); //returns the same memory address as the NSLog in the previous function
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
glOrtho(0.5, 0.5, 1.0, 1.0, -1.0, 1.0);
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glEnable(GL_DEPTH_TEST);
glGetIntegerv(GL_DEPTH_BITS, &depth);
NSLog(#"%i bits depth", depth); // returns 0
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
//drawing code here
// Call super to finalize the drawing. By default all it does is call glFlush().
[super drawInCGLContext:glContext pixelFormat:pixelFormat forLayerTime:timeInterval displayTime:timeStamp];
}
The program compiles fine and displays the content, but without the depth testing. Is there something extra I have to do to get this to work? Or is my entire approach wrong?

Answer 1

Looks like I was overriding the wrong method. To obtain the required depth buffer one should override the copyCGLPixelFormatForDisplayMask like so:
- (CGLPixelFormatObj)copyCGLPixelFormatForDisplayMask:(uint32_t)mask {
CGLPixelFormatAttribute attributes[] =
{
kCGLPFADepthSize, 24,
0
};
CGLPixelFormatObj pixelFormatObj = NULL;
GLint numPixelFormats = 0;
CGLChoosePixelFormat(attributes, &pixelFormatObj, &numPixelFormats);
if(pixelFormatObj == NULL)
NSLog(#"Error: Could not choose pixel format!");
return pixelFormatObj;
}
Based on the code here.