Proper way to implement zoom in CA?

FROM : Colin Cornaby
DATE : Wed Nov 07 08:27:25 2007

(I sent this message to the Quartz list and didn't get any response. 
Given that this list is higher traffic and seems to be talking about 
CA I'm reposting it here.)

I wrote an application under OpenGL under Tiger that I have been 
porting to CoreAnimation over the last four months. I basically found 
that the GL engine I was writing replicated most of the  layering 
functionality of CoreAnimation, so it was just easier to move the 
project entirely over. (And implicit animations are pretty...)

My experience so far with CoreAnimation has been good, but the one 
thing I have never really gotten working again is zoom. In my OpenGL 
version, I would simply change the bounds of the gl viewport in order 
to change the scale of the entire composition.

CoreAnimation seems to have a facility to do something similar using 
setBounds and autoresizingMask, but so far I haven't gotten it 
working. I set my sublayers resizing mask for width and height, and 
then adjust the bounds of the parent layer, and my layers don't 
actually draw at the correct size.

The admittedly cheap hack I've been using in the mean time is simply 
doing a 3D transform and pushing the layer forward or away on the Z 
axis. I have a few issues with this approach. First, layers don't 
redraw with new bounds when I zoom in. So when I zoom in to layers 
that are drawn on the fly, they are all pixelated because they are 
still being drawn at a 1.0 scale bounds. The second issue is that 
there are some layers that I would like not to scale. It seems like 
the setBounds/autoresizingMask route would also address this, as it 
looks like I can adjust scaling behavior on a per layer basis.

I'm hoping all of this makes sense to someone. :) I'm just looking for 
a few pointers if anyone else has run into this issue.

Thanks,
Colin