Animation 如何沿路径设置contentsRect属性的动画？

我加载了一个png精灵表和相应的plist文件，我正在尝试设置CALayer的contentsRect属性的动画，以显示上述aprite表中的精灵动画。下面是一个代码：

CGFloat width = myLayer.frame.size.width;
CGFloat height = myLayer.frame.size.height;
myLayer.bounds = CGRectMake( 0, 0, width, height );
myLayer.contentsGravity = kCAGravityCenter;
myLayer.contents=(id)pImage; // This is my sprite sheet


CAKeyframeAnimation *keyFrameContentsRectAnimation = [CAKeyframeAnimation animationWithKeyPath:@"contentsRect"];
keyFrameContentsRectAnimation.path = pAnimationPath; // This is a path to animate on
keyFrameContentsRectAnimation.values = pRects; // This is an array of normalized CGRects representing sprite sheet
keyFrameContentsRectAnimation.fillMode = kCAFillModeRemoved;
keyFrameContentsRectAnimation.calculationMode = kCAAnimationDiscrete;
keyFrameContentsRectAnimation.duration=pAnimationDuration;
keyFrameContentsRectAnimation.repeatCount = 1;

只要我禁用路径动画（即，从keyFrameContentsRectAnimation中注释掉路径属性），上述代码似乎就能按预期工作-动画工作，内容在精灵工作表中移动

但问题是：我的所有精灵都需要在层帧内进行一些偏移，以使动画看起来正确（偏移量根据透明度裁剪而变化）

所以我想，如果我从这些偏移点创建一条路径，并将其放入动画的路径属性中，应该可以解决这个问题。不幸的是，事实并非如此。。。

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一旦我添加路径属性，我就会看到整个精灵表图像，而不是精灵动画。。。我错过了什么？

好吧，经过一些阅读和实验，我有了一个有效的解决方案。。。为了让精灵显示在正确的位置，我必须将另一个动画添加到动画组中，并将CALayer剪辑到精灵的尺寸：

myLayer.bounds = CGRectMake( 0, 0, 256.0, 256.0 ); //my sprite dimentions

myLayer.contentsGravity = kCAGravityCenter;
myLayer.contents=(id)pImage; // This is my sprite sheet


CAKeyframeAnimation *keyFrameContentsRectAnimation = [CAKeyframeAnimation animationWithKeyPath:@"contentsRect"];

keyFrameContentsRectAnimation.values = pRects; // This is an array of normalized CGRects representing sprite sheet
keyFrameContentsRectAnimation.fillMode = kCAFillModeRemoved;
keyFrameContentsRectAnimation.calculationMode = kCAAnimationDiscrete;
keyFrameContentsRectAnimation.duration=pAnimationDuration;
keyFrameContentsRectAnimation.repeatCount = 1;  

CAKeyframeAnimation* kfanim = [CAKeyframeAnimation animationWithKeyPath:@"contents"];
kfanim.path = pAnimationPath;
kfanim.values = pRects;
kfanim.fillMode = kCAFillModeBoth;
kfanim.calculationMode = kCAAnimationDiscrete;
kfanim.duration=pAnimationDuration;
kfanim.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];


NSArray *animations = [NSArray arrayWithObjects:keyFrameContentsRectAnimation,
                       kfanim, nil];

CAAnimationGroup *animationGroup = [CAAnimationGroup animation];
[animationGroup setDuration:pAnimationDuration];
[animationGroup setRepeatCount: 1];
[animationGroup setAnimations:animations];