Trouble getting CALayers to be transparent

FROM : vProgrammingLists
DATE : Tue Jan 08 20:47:49 2008

I want to put  transparent CALayers over an OpenGL Texture and use
CAAnimation to fade them in. I thought it would be possible to use
Core Text in the CALayers to accomplish this.

I can get Core Text into the CALayers. I can use CAAnimation to fade
them in, but I cannot get the layers to be transparent.

I have an existing/in progress hybrid Cocoa OpenGL appliction. Before
Leopard, I was showing large amounts of scrollable text over an
OpenGL texture by overlaying a transparent window (making it a child
window) and adding a subview - an NSScrollView with a transparent
background, into the child window which displayed my text.

When Leopard came along, I thought it would be nice to animate the
opacity resulting in a gentle fade in for each 'page' of text. But
every experiment I have tried results in the text displayed on a
white opaque background. Even without the CAAnimation.

I am sure that I am just missing some fundamental simple point. I
hope someone can help.

I have tried:
1. just telling the existing 'NSScrollview' in the transparent Child
window  - setWantsLayer:YES
Result - animates fading in text with white Opaque background.

2. Subclassing CALayer and drawing the text in a
drawInContext:(CGContextRef)context
Using Coretext. Result - animates fading in Text with white Opaque background.

2a. telling the new view that contains the subclassed CALayer -
[theView setBackgroundColor:[NSColor clearColor]];

2b. in my drawInContext:(CGContextRef)context: I try to fill the
rectangle of the view with a transparent CGColor:
  CGContextBeginTransparencyLayer (context, NULL);
  CGContextClearRect(context, frame);
etc. until
  CGContextEndTransparencyLayer (context);
or
   CGFloat transparentValues[4] = {0.0, 0.0, 0.0, 0.0};
   CGColorSpaceRef space =
CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB);
   CGColorRef clearOne  = CGColorCreate(space, transparentValues);

Result: animates fading in Text with white Opaque background.

2c. tried adding a compositing filter to the layer compositing 'srcOver'
Result: animates fading in Text with white Opaque background.

I have tried creating a coloured background, and the colour draws
sort of translucently over the text and the white opaque background.

Can anyone help? Is it a CoreText bug with CALayers or have I missed
something really fundamental?

Vickie