Calculate rotation angle for anchor point - ios

Question

I got stuck with a problem where I need to reposition views to predefined locations.
All views have a UIPanGestureRecognizer and a UIRotationGestureRecognizer and are positioned/rotated inside the controllers view. Upon a certain event the views should move to a new position with a new rotation angle.
Everything works fine but a soon as one of the gesture recognizer was active and thus the anchorPoint has changed repositioning/rotation fails.
Here is my method I try to use to take the shift in the anchorPoint into account.
- (CGPoint)centerPointWithInVisibleAreaForPoint:(CGPoint)point
{
CGPoint anchorP = self.layer.anchorPoint;
anchorP.x -= 0.5;
anchorP.y -= 0.5;
CGRect rect = self.bounds;
CGFloat widthDelta = CGRectGetWidth(self.bounds) * anchorP.x;
CGFloat heightDelta = CGRectGetHeight(self.bounds) * anchorP.y;
CGPoint newCenter = CGPointMake(point.x + widthDelta, point.y + heightDelta);
return newCenter;
}
The controller asks for the corrected center point and sets the center value of the view. Afterwards the rotation transform is set using CGAffineTransformConcat(view.transform, CGAffineTransformMakeRotation(differenceAngle)).
I think the problem is caused by the fact that the predefined target angle is based on a rotation around the center which is obviously different when rotated around a different anchorPoint, but I don't know how to compensate for that.

Answer 1

The only solution I found (and it is after all the most easiest one) is to reset the anchorPoint to 0.5/0.5 and correct the position accordingly.
- (void)resetAnchorPoint
{
if (!CGPointEqualToPoint(self.layer.anchorPoint, CGPointMake(0.5, 0.5))) {
CGFloat width = CGRectGetWidth(self.bounds);
CGFloat height = CGRectGetHeight(self.bounds);
CGPoint newPoint = CGPointMake(width * 0.5, height * 0.5);
CGPoint oldPoint = CGPointMake(width * self.layer.anchorPoint.x, height * self.layer.anchorPoint.y);
newPoint = CGPointApplyAffineTransform(newPoint, self.transform);
oldPoint = CGPointApplyAffineTransform(oldPoint, self.transform);
CGPoint position = self.layer.position;
position.x += (newPoint.x - oldPoint.x);
position.y += (newPoint.y - oldPoint.y);
[CATransaction setDisableActions:YES];
self.layer.position = position;
self.layer.anchorPoint = CGPointMake(0.5, 0.5);
[CATransaction setDisableActions:NO];
}
}