zooming from a particular point - iphone

Question

I am using this code to zoom from a particular point
CGPoint getCenterPointForRect(CGRect inRect)
{
CGRect screenRect = [[UIScreen mainScreen] bounds];
return CGPointMake((screenRect.size.height-inRect.origin.x)/2,(screenRect.size.width-inRect.origin.y)/2);
}
-(void) startAnimation
{
CGPoint centerPoint = getCenterPointForRect(self.view.frame);
self.view.transform = CGAffineTransformMakeTranslation(centerPoint.x, centerPoint.y);
self.view.transform = CGAffineTransformScale( self.view.transform , 0.001, 0.001);
[UIView beginAnimations:nil context:nil];
[UIView setAnimationDuration:kTransitionDuration];
self.view.transform = CGAffineTransformIdentity;
[UIView commitAnimations];
}
Its not working. What is the correct way to do zooming from a particular point.

Answer 1

I think that, if I've diagnosed your problem correctly, you're getting a scaling animation where the view starts tiny and at a point, then scales and moves to the centre of the screen exactly like you want, but the point it starts at is incorrect?
First of all, views scale around their centre. So if you took out the translation and hence reduced the code you have to:
self.view.transform = CGAffineTransformMakeScale( 0.001, 0.001);
And your view ends up taking up the whole screen then it'll remain centred on the middle of the screen, sort of a little as though it's a long way away and you're heading directly towards it.
Supposing you instead want it to grow and move to the centre of the screen from (x, y) then you need something more like:
CGPoint locationToZoomFrom = ... populated by you somehow ...;
CGPoint vectorFromCentreToPoint = CGPointMake(
locationToZoomFrom.x - self.view.center.x,
locationToZoomFrom.y - self.view.center.y);
self.view.transform = CGAffineTransformMakeTranslation(vectorFromCentreToPoint.x, vectorFromCentreToPoint.y);
self.view.transform = CGAffineTransformScale( self.view.transform , 0.001, 0.001);
Where locationToZoomFrom will be the initial centre of the view and its normal centre as per its frame will be the destination.