How to keep on rotating a view with a CAKeyFrameAnimation?

Question

I try to do this: There is an view which has been rotated already to some value, lets say 15 degrees.

Imagine a view rotated by 15 degrees.

Next, I only know, that I want this view to rotate from it's current rotation to 40 degrees.

Imagine how that view now rotates from 15 to 40 degrees.

For practice, I want to do that with CAKeyFrameAnimation. But the thing is, all I can do there is to hard-specify from where to where. There's no convenient "pick up current state" thing like UIView animations have, right? How would I go about it?

Also, I want to specify always 3 keyframes for that rotation, no matter how much the needed amount of rotation is.

Imagine how that view rotates from 15 to 40 degrees, using 3 keyframes to do so

But another big problem: It might happen, that another animation has to kick in with a different target. lets say a view is currently rotation from 20 to 100 degrees, and just somewhere inbetween the animation a new animation is kicked and wants that view to go to 15 degrees. With UIView animations that's simple. How to do that with CAKeyFrameAnimation?

Basically I want it to behave like UIView animations which pick up current state ;)

CALayer* theLayer = rotatedView.layer;

CAKeyframeAnimation* animation;
animation = [CAKeyframeAnimation animationWithKeyPath:@"transform.rotation.z"];

animation.duration = 2;
animation.repeatCount = 1;
animation.removedOnCompletion = NO;
animation.fillMode = kCAFillModeForwards;

animation.values = [NSArray arrayWithObjects:
                    [NSNumber numberWithFloat:(10.0 / 180.0) * M_PI],
                    [NSNumber numberWithFloat:(20.0 / 180.0) * M_PI],
                    [NSNumber numberWithFloat:(30.0 / 180.0) * M_PI], nil];

[theLayer addAnimation:animation forKey:@"transform.rotation.z"];

score 1 · Accepted Answer · edited May 23 '17 at 11:48

1

You can use theLayer.transform or theLayer.affineTransform to get the current transform matrix (before the animation), then use iphone sdk CGAffineTransform getting the angle of rotation of an object to get the angle to start with.

edited May 23 '17 at 11:48

Community

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answered Feb 02 '10 at 16:01

kennytm

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score 0 · Answer 2 · edited May 23 '17 at 12:06

You can obtain the starting angle for use in setting up your animation either using code like what I provide in this answer:

CATransform3D rotationTransform = [theLayer transform];
float angle;
if (rotationTransform.m11 < 0.0f)
        angle = 180.0f - (asin(rotationTransform.m12) * 180.0f / M_PI);
else
        angle = asin(rotationTransform.m12) * 180.0f / M_PI;

or using the simpler helper keypath method suggested here:

float currentAngle = ([[theLayer valueForKeyPath:@"transform.rotation.z"] floatValue] * 180.0f / M_PI);

If you are adding this animation to one already in progress, you will need to query the current angle of theLayer's presentationLayer, instead of theLayer directly. The presentationLayer for a CALayer reflects the current state of a layer mid-animation.

How to keep on rotating a view with a CAKeyFrameAnimation?

2 Answers2