Re: CoreAnimation with and manual animation...

FROM : Jens Alfke
DATE : Wed Apr 02 00:17:41 2008

On 1 Apr '08, at 10:44 AM, Jesse Grosjean wrote:

> n my app it seems like it would be simpler to just setup a timer and 
> just directly update the ships position based on it's velocity for 
> each time interval from my timer. I'd still want to use the built in 
> core animation animations for other properties such as transparency, 
> filters, etc. But for layer position it seems like it would be 
> easiest to control that directly...


You're right. Last year I was fooling around with hooking CA up to a 
2D physics engine, and I just let the engine tell me where and when to 
position the objects, and set their position properties accordingly.

For best results, disable animations for this, otherwise CA will try 
to interpolate positions and things won't move correctly. I was doing 
this by using a CATransaction to disable all animations, but I think 
in hindsight it might be better just to to adjust the layers' 
animation dictionaries to clear out the animation for the "position" 
key.

(Using an existing physics engine is a great way to go, if you want to 
do this. I was using Box2D, but there's another similar one called 
Chipmunk. The math for this stuff gets really hairy — I've just 
started reading "Physics For Game Developers", and it's fascinating 
but I'm so glad I don't have to implement that myself!)

—Jens