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iphonecocoacore-animation

Core Animation rotating a layer around arbitrary point

How can I rotate a layer using Core Animation around an arbitrary point? ( In my case a point that is not inside the layer I want to rotate )

I prefer doing this without changing the anchor point, because unless I get something wrong every time I change the anchor point it also changes the position of the layer.

I tried something like that but it didn't work:

[UIImageView beginAnimations:nil context:nil];
CATransform3D rotationTransform = CATransform3DIdentity;
rotationTransform = CATransform3DTranslate(rotationTransform, 0.0, -100.0, 0.0);
rotationTransform = CATransform3DRotate(rotationTransform, DegreesToRadians(180),
                        0.0, 0.0, 1.0);
rotationTransform = CATransform3DTranslate(rotationTransform, 0.0, 100.0, 0.0)
shape1.layer.transform = rotationTransform;
[UIImageView commitAnimations];

It looks like the rotation axis is moving during the rotate.

Solution

  • I finaly did it by creating a new bigger layer with it's center at my rotation axis and setting the layer i want to rotate as it's sub layer.

    Then I rotate the bigger layer instead of the sub layer