how find position of CAlayer during animation?

Question

I am implementing game application.In which i am using layer for animation.

CGMutablePathRef path = CGPathCreateMutable();
CGPathMoveToPoint(path, NULL, previousValuex, previousValue);
CGPathAddLineToPoint(path, NULL, valuex, value);
previousValue=value;
previousValuex=valuex;

CAKeyframeAnimation *animation;
animation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
animation.path = path;
animation.duration =1.0;
animation.repeatCount = 0;
//animation.rotationMode = kCAAnimationRotateAutoReverse;
animation.calculationMode = kCAAnimationPaced;

// Create a new layer for the animation to run in.
CALayer *moveLayer = [imgObject layer];
[moveLayer addAnimation:animation forKey:@"position"];

Now i want to find layer position during animation?Is it possibel?please help me.

Answer 1

In order to find the current position during an animation, you will need to look at the properties of the layer's presentationLayer . The properties of the layer itself will only reflect the final target value for an implicit animation, or the initial value before you applied the CABasicAnimation . The presentationLayer gives you the instantaneous value of whatever property you are animating.

For example,

CGPoint currentPosition = [[moveLayer presentationLayer] position];

will get you the current position of the layer as it is animating about your path. Unfortunately, I believe it is difficult to use key-value observing with the presentation layer, so you may need to manually poll this value if you want to track it.

Answer 2

我从未尝试过这样做，但是您应该能够在动画过程中（也许通过KVO吗？）监视CALayer的frame属性（或position ， bounds或anchorPoint ，具体取决于您的需求）。

Answer 3

If your CALayer is inside another CALayer you may need to apply the affineTransform of the parent CALayer to get the position of the child CALayer like this:

// Create your layers
CALayer *child = CALayer.layer;
CALayer *parent = self.view.layer;
[parent addSubLayer:child];

// Apply animations, transforms etc...

// Child center relative to parent
CGPoint childPosition = ((CALayer *)child.presentationLayer).position;

// Parent center relative to UIView
CGPoint parentPosition = ((CALayer *)parent.presentationLayer).position;
CGPoint parentCenter = CGPointMake(parent.bounds.size.width/2.0, parent.bounds.size.height /2.0);

// Child center relative to parent center
CGPoint relativePos = CGPointMake(childPosition.x - parentCenter.x, childPosition.y - parentCenter.y);

// Transformed child position based on parent's transform (rotations, scale etc)
CGPoint transformedChildPos = CGPointApplyAffineTransform(relativePos, ((CALayer *)parent.presentationLayer).affineTransform);

// And finally...
CGPoint positionInView = CGPointMake(parentPosition.x +transformedChildPos.x, parentPosition.y + transformedChildPos.y);

This code is based on code I just wrote in which the parent CALayer was rotating and the position was changing and I wanted to get the position of a child CALayer relative to a touch position in the UIView the parent belonged to. So this is the basic idea, but I haven't actually run this pseudocode version.