Timer-Based Animation - iOS Core Animation - page 243

//start the timer
self . lastStep = CACurrentMediaTime ();
self . timer = [ CADisplayLink displayLinkWithTarget : self
selector : @selector (step:)];
[ self . timer addToRunLoop :[ NSRunLoop mainRunLoop ]
forMode : NSDefaultRunLoopMode ];
}
void updateShape( cpShape *shape, void *unused)
{
//get the crate object associated with the shape
Crate *crate = ( __bridge Crate *)shape-> data ;
//update crate view position and angle to match physics shape
cpBody *body = shape-> body ;
crate. center = cpBodyGetPos (body);
crate. transform = CGAffineTransformMakeRotation ( cpBodyGetAngle (body));
}
- ( void )step:( CADisplayLink *)timer
{
//calculate step duration
CFTimeInterval thisStep = CACurrentMediaTime ();
CFTimeInterval stepDuration = thisStep - self . lastStep ;
self . lastStep = thisStep;
//update physics
cpSpaceStep ( self . space , stepDuration);
//update all the shapes
cpSpaceEachShape ( self . space , & updateShape , NULL );
}
@end