Rotating image round a fix point - iphone

Question

Firstly I am new to Objective C, any help will be most appreciated. I trying to write a Gauge app (which will eventually show the Angle of the phone). The issue I have is when I rotate the Needle image, it rotates to the correct angle, but not from the Anchor point - the image moves position. Even when I move, say from 0 dregs to 90 and back to 0, the image is does not end up back in its original position! The code I am using is below: .
(PS I am only currently only running the app on the simulator)
*** Rotate Invoked by ....
// Rotate Image
[self rotateImage:_imgNeedle duration: vAnimationDuration curve: UIViewAnimationCurveLinear degrees:vValue];
-(void)rotateImage:(UIImageView *)image
duration:(NSTimeInterval)duration
curve:(int)curve
degrees:(CGFloat)degrees
{
// Setup the animation
[self setAnchorPoint:CGPointMake(.44,.85) forView:image];
// image.transform = CGAffineTransformMakeRotation(d2r(degrees));
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:duration];
[UIView setAnimationCurve:curve];
[UIView setAnimationBeginsFromCurrentState:YES];
// The transform matrix
CGAffineTransform transform = CGAffineTransformMakeRotation(d2r(degrees));
image.transform = transform;
// Commit the changes
[UIView commitAnimations];
}
// Set Anchor Point
-(void)setAnchorPoint:(CGPoint)anchorPoint forView:(UIView *)view
{
CGPoint newPoint = CGPointMake(view.bounds.size.width * anchorPoint.x, view.bounds.size.height * anchorPoint.y);
CGPoint oldPoint = CGPointMake(view.bounds.size.width * view.layer.anchorPoint.x, view.bounds.size.height * view.layer.anchorPoint.y);
newPoint = CGPointApplyAffineTransform(newPoint, view.transform);
oldPoint = CGPointApplyAffineTransform(oldPoint, view.transform);
CGPoint position = view.layer.position;
position.x -= oldPoint.x;
position.x += newPoint.x;
position.y -= oldPoint.y;
position.y += newPoint.y;
view.layer.position = position;
view.layer.anchorPoint = anchorPoint;
}

Answer 1

I am not sure about the layer position, but when I change the anchorPoint, the frame changes, so I will adjust the frame.
-(void)setAnchorPoint:(CGPoint)anchorPoint forView:(UIView *)view
{
CGPoint newPoint = CGPointMake(view.bounds.size.width * anchorPoint.x, view.bounds.size.height * anchorPoint.y);
CGPoint oldPoint = CGPointMake(view.bounds.size.width * view.layer.anchorPoint.x, view.bounds.size.height * view.layer.anchorPoint.y);
newPoint = CGPointApplyAffineTransform(newPoint, view.transform);
oldPoint = CGPointApplyAffineTransform(oldPoint, view.transform);
/*
CGPoint position = view.layer.position;
position.x -= oldPoint.x;
position.x += newPoint.x;
position.y -= oldPoint.y;
position.y += newPoint.y;
view.layer.position = position;
*/
view.frame = CGRectOffset(view.frame, newPoint.x-oldPoint.x, newPoint.y-oldPoint.y);
view.layer.anchorPoint = anchorPoint;
}
And also if you want to go back to the original position with multiple calling of rotateImage, I think you should only set the anchor point once before that. Since if you make two separate animation with the same rotateImage method, the anchor point will be recalculated with your current implementation.
-(void)rotateImage:(UIImageView *)image
duration:(NSTimeInterval)duration
curve:(int)curve
degrees:(CGFloat)degrees
{
// Setup the animation
// [self setAnchorPoint:CGPointMake(.44,.85) forView:image];
// image.transform = CGAffineTransformMakeRotation(d2r(degrees));
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:duration];
[UIView setAnimationCurve:curve];
[UIView setAnimationBeginsFromCurrentState:YES];
// The transform matrix
CGAffineTransform transform = CGAffineTransformMakeRotation(d2r(degrees));
image.transform = transform;
// Commit the changes
[UIView commitAnimations];
}