I'm failing to understand I think exactly what CALayer gives me and thus whether or not it's good for something I'm working on. I've read the documentation pretty thoroughly I think but I'm not getting it.
Target here is IPhone OS, which may matter. Concept is a view with a number of 'objects' drawn on it, 5, 15, 15, 20 .. that's about it. They can move around, they can have some kind of z-ordering amongst themselves. The objects need to draw themselves instead of having one big drawRect: statement. One way to do it would be to have one UIView which asks each object "are you in this rectangle" and if so "please draw nicely" at the correct place on the UIView's layer. I was a bit bothered however what would happen if I move an object from one point to another, at the least I'd have to invalidate the entire rectangle from the corner the thing started, to where it ended up to make sure everything it passed over gets redrawn and perhaps even that's not enough. So I read about CALayers and was trying to understand whether I get something for free over and above the method just described. Do CALayers retain their content so that as they are moved they don't redraw themselves but are just recomposited in a different area of the screen? That would of course be a win as the first method means redrawing the object in different locations on the UIView's layer, recomposition means I drew it once and that's it. How about other layers, if the content is retained, then I wouldn't have to redraw those either, the entire movement just becomes a compositing exercise by the GPU. If CALayers don't retain content (or perhaps only a limited number of them can if there's a GPU limitation) then there would still be redrawing calls but, it seems, I wouldn't have to worry about figuring out what layers need redraws (ie figuring out the big dirty rectangle), something else would be working that out and just telling the affected CALayers to redraw. Am I understanding CALayer at all or am I totally out in the woods here and have misunderstood the concepts? Is there a piece of documentation which explains these points which I either missed, or failed to understand properly. Thanks. _______________________________________________ Cocoa-dev mailing list ([email protected]) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [email protected]
