I want to animate the drawing of  CGPath in a UIView, so it looks as if it's 
being drawn. I have the UIView, I have the CGPath, I am able to split the 
CGPath at any point from 0 to 100% into that which should be drawn and that 
which shouldn't yet, that's all done, so I can, fairly efficiently, call 
-(CGPath)[ myObject fractionalPath:(CGFloat)fraction ] and get a path. 

The idea is to call setNeedsDisplay on the UIView from time to time, then 
figure out, when I get my -drawRect call how far through the animation I am, 
call fractionalPath: for that fraction of the total animation time, and draw 
it. The path isn't that complex, it doesn't take very long to draw and I'm 
compositing already-fully-drawn paths into a backing UIImage so there's only 
one 'live one' at any time. 

The bit I'm not sure about is how to sync this up with the natural framerate of 
the device. I could call setNeedsDisplay on a timer, or with a delay after each 
drawRect, but there is surely a better way to do this, is there not? If I do 
call setNeedsDisplay a lot, will I only get drawRect at most at the natural 
framerate of the device. 

Is there an obvious technology I'm missing? This is a pretty simple way to do a 
quick animation of a single path, so OpenGL or anything like that is massive 
overkill and I didn't see anything CALayer would give me which would help, but 
wondered if I'd missed something there as that does have the concept of 
animating a property, even a custom one, between two values and I wondered if I 
could hook into that. 
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