iPhone: Layering a transparent openGL view on top

Question

I am working on iPhone app and I have an openGL view rendering on top of a regular UIView. It's working, but I can't seem to get the openGL view to have a transparent background that shows the UIView underneath. Instead, I get a big black box.

I have tried setting the background color to UIColor clearColor, I've set opaque to NO, I've set glClearColor to 0.0,0.0,0.0,0.0.

I think I'm misunderstanding/misusing something related to blend modes, but I'm not sure. Can anyone give me a bit of sample code which shows how to do this?

Thanks in advance.

Answer 1

Here's what I had to do to get this to work:

eaglLayer.opaque = NO;      
eaglLayer.drawableProperties = [NSDictionary dictionaryWithObjectsAndKeys:
                                kEAGLColorFormatRGBA8, kEAGLDrawablePropertyColorFormat, nil];
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);

And incase you're doing what I was doing and are trying to test it with the GLGravity demo, there's another call to glClearColor(0.0f, 0.0f, 0.0f, 1.0f); every time drawView is called -- so make sure you change that one to glClearColor(0.0f, 0.0f, 0.0f, 0.0f); too! :)

Answer 2

Add those in EAGLView.m

-(id)initWithCoder:(NSCoder*)coder

self.opaque = NO;
self.backgroundColor = [UIColor clearColor];

CAEAGLLayer *eaglLayer = (CAEAGLLayer *)self.layer;
eaglLayer.opaque = NO;

CGColorSpaceRef rgb = CGColorSpaceCreateDeviceRGB();
const CGFloat myColor[] = {0.0, 0.0, 0.0, 0.0};
eaglLayer.backgroundColor = CGColorCreate(rgb, myColor);
CGColorSpaceRelease(rgb);

Answer 3

Check the color format of your view. If you’ve set it to kEAGLColorFormatRGB565 via the drawableProperties dictionary, the alpha channel of the view’s contents will be implicitly treated as 1.0, regardless of what you draw into it.