iphone - how to rotate CALayer at one point

Question

how to rotate CALayer at one selected point.

Answer 1

CATransform3D transform = CATransform3DIdentity;
transform = CATransform3DTranslate(transform, rotationPoint.x-center.x, rotationPoint.y-center.y, 0.0);
transform = CATransform3DRotate(transform, rotationAngle, 0.0, 0.0, -1.0);
transform = CATransform3DTranslate(transform, center.x-rotationPoint.x, center.y-rotationPoint.y, 0.0);

Where center is the center of your layer, rotationAngle is in radians (positive is counterclockwise), and rotationPoint is the point about which you wish to rotate. center and rotationPoint are in the coordinate space of the containing view.