Re: CoreAnimation efficiency

FROM : Jens Alfke
DATE : Thu Mar 06 22:16:28 2008

On 6 Mar '08, at 2:43 AM, Half Activist wrote:

>     As I'm investigating on which drawing techniques to use for a 
> software I'm planing to create,
>     imagine a kind of vector drawing program (that's not really that 
> but a somewhat similar).
>     In its actual version, all drawing relies on NSBezierPath/Quartz 
> primitives and is really fast.
>     Now, I'd like to use CALayers and CoreAnimation extensively


I've used CA but am not an expert on its implementation. Here's my 
take. Large numbers of layers aren't a problem. Large numbers of 
layers *with custom drawing* would be a problem. That's because such a 
layer will have a pixmap backing it, and CA will try to keep the 
layers' pixmaps in the graphics coprocessor's memory, which is rather 
limited.

Bezier paths don't seem like a good candidate for representing via 
individual CA layers. A large but simple path can be represented as a 
few dozen bytes of memory in an NSBezierPath object, but would require 
megabytes of memory for a pixmap. Drawing the pixmap will also require 
processing a lot more pixels than drawing the path; if the path is 
unfilled, it might be hundreds of times as many.

(On the other hand, layers consisting of solid colors, borders, round 
corners and/or text are very cheap, because they're drawn using OpenGL 
primitives and don't need a pixmap.)

—Jens