Is it possible to get a 16-bit depth buffer on the iPhone?

Question

Hi!

We're making a game using cocos2d but are having problems with the depth buffer. I'm trying to setup a 16-bit depth buffer on the iPhone but so far I only get 24-bit depth.

The reason I want 16-bit depth buffer is:

• A: I don't need the precision of 24-bit.
• B: I'm hoping it will be faster.

This is how I set the depth format in cocos2d:

[[CCDirector sharedDirector] setDepthBufferFormat:kDepthBuffer16];

Which at some point ends up in EAGLView (v1.3)

glGenRenderbuffersOES(1, &_depthBuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, _depthBuffer);
glRenderbufferStorageOES(GL_RENDERBUFFER_OES, _depthFormat, newSize.width, newSize.height);
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, _depthBuffer);

Where _depthFormat is GL_DEPTH_COMPONENT16_OES (verified while debugging)

And here's how I check the number of bits:

GLint depthBufferBits;
glGetIntegerv( GL_DEPTH_BITS, &depthBufferBits );
NSLog( @"Depth buffer bits: %d", depthBufferBits );

And the output is:

Depth buffer bits: 24

What am I missing? I've tried the same code on iPod Touch (2nd gen) and iPhone 3GS, always comes back as 24 bit.

Update:

I've now updated cocos2d to the latest version from the GIT repo. Here's how I initialize the director and window:

- (void) applicationDidFinishLaunching:(UIApplication*)application
{
    // Init the window
    window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    [[UIApplication sharedApplication] setIdleTimerDisabled:YES];
    // cocos2d will inherit these values
    [window setUserInteractionEnabled:YES]; 
    [window setMultipleTouchEnabled:YES];

    [CCDirector setDirectorType:CCDirectorTypeDisplayLink];

    CCDirector* director = [CCDirector sharedDirector];

    [director setAnimationInterval:1.0/60];
    [director setDisplayFPS:YES];

    EAGLView *glView = [EAGLView viewWithFrame:[window bounds]
                                   pixelFormat:kEAGLColorFormatRGBA8                // RGBA8 color buffer
                                   depthFormat:GL_DEPTH_COMPONENT16_OES   // 16-bit depth buffer
                            preserveBackbuffer:NO];

    [director setOpenGLView:glView];
    [director setProjection:kCCDirectorProjection2D];

    [window addSubview:glView];
    [window makeKeyAndVisible];     

    [CCTexture2D setDefaultAlphaPixelFormat:kTexture2DPixelFormat_RGBA8888];

    [director runWithScene:[LevelScene scene]];
}

Still getting a 24-bit depth buffer according to glGetIntegerv( GL_DEPTH_BITS, &depthBufferBits );

Answer 1

I'm not sure about the internals but setDepthBufferFormat is deprecated. I can also imagine that it's simply (no longer) possible to change the depth buffer after the GL view has been created. With Cocos2D v0.99.5 beta 3 the initialization has changed quite a bit. I suggest you update to the latest version, even though it's beta.

Then take a look here: http://www.cocos2d-iphone.org/wiki/doku.php/prog_guide:setup_buffers

The important part is the initialization of the EAGLView, where you can set the depth buffer:

EAGLView *glView = [EAGLView viewWithFrame:[window bounds]
                               pixelFormat:kEAGLColorFormatRGBA8
                               depthFormat:GL_DEPTH_COMPONENT16_OES
                        preserveBackbuffer:NO];