从当前 CAAnimation 的状态开始新的 CAAnimation

Question

我使用一对 CALayers 作为图像蒙版，允许我以设定的速度为灯泡填充或排空设置动画，同时也跟随当前的触摸位置。也就是说，一个蒙版会随着触摸跳动，而另一个则滑到那个位置。由于我使用了显式动画，因此在添加动画时我不得不设置遮罩滑动遮罩的位置。这意味着如果我开始填充，然后在填充完成之前开始清空，则清空将从完成的填充位置开始（反之亦然）。

有没有办法获取动画的位置，设置动画每一步的位置，或者让新动画从活动动画的当前状态开始？

处理动画的代码如下：

- (void)masksFillTo:(CGFloat)height {
    // Clamp the height we fill to inside the bulb. Remember Y gets bigger going down.
    height = MIN(MAX(BULB_TOP, height), BULB_BOTTOM);

    // We can find the target Y location by subtracting the Y value for the top of the
    // bulb from the height.
    CGFloat targetY = height - BULB_TOP;

    // Find the bottom of the transparent mask to determine where the solid fill
    // is sitting. Then find how far that fill needs to move.
    // TODO: This works with the new set position, so overriding old anime doesn't work
    CGFloat bottom = transMask.frame.origin.y + transMask.frame.size.height;

    // If the target is above the bottom of the solid, we want to fill up.
    // This means the empty mask jumps and the transparent mask slides.
    CALayer *jumper;
    CALayer *slider;
    if (bottom - targetY >= 0) {
        jumper = emptyMask;
        slider = transMask;

        // We need to reset the bottom to the emptyMask
        bottom = emptyMask.frame.origin.y + emptyMask.frame.size.height;
    } else {
        jumper = transMask;
        slider = emptyMask;
    }

    [jumper removeAllAnimations];
    [slider removeAllAnimations];

    CGFloat dy = bottom - targetY;

    [CATransaction begin]; 
    [CATransaction setValue:(id)kCFBooleanTrue forKey:kCATransactionDisableActions];
    [jumper setPosition:CGPointMake(jumper.position.x, jumper.position.y - dy)];
    [self slideMaskFillTo:height withMask:slider]; // Do this inside here or an odd flash glitch appears.
    [CATransaction commit];
}

// TODO: Always starts from new position, even if animation hasn't reached it.
- (void)slideMaskFillTo:(CGFloat)height withMask:(CALayer *)slider {
    // We can find the target Y location by subtracting the Y value for the top of the
    // bulb from the height.
    CGFloat targetY = height - BULB_TOP;

    // We then find the bottom of the mask.
    CGFloat bottom = slider.frame.origin.y + slider.frame.size.height;

    CGFloat dy = bottom - targetY;

    // Do the animation. Animating with duration doesn't appear to work properly.
    // Apparently "When modifying layer properties from threads that don’t have a runloop, 
    // you must use explicit transactions."
    CABasicAnimation *a = [CABasicAnimation animationWithKeyPath:@"position"];
    a.duration = (dy > 0 ? dy : -dy) / PXL_PER_SEC; // Should be 2 seconds for a full fill
    a.fromValue = [NSValue valueWithCGPoint:slider.position];
    CGPoint newPosition = slider.position;
    newPosition.y -= dy;
    a.toValue = [NSValue valueWithCGPoint:newPosition];
    a.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
    [slider addAnimation:a forKey:@"colorize"];

    // Update the actual position
    slider.position = newPosition;
}

还有一个如何调用的示例。请注意，这意味着它可以称为中间动画。

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];
    CGPoint point = [touch locationInView:self.view];

    [self masksFillTo:point.y];
}

如果有人发现它相关，这就是图像和蒙版的创建。

// Instantiate the different bulb images - empty, transparent yellow, and solid yellow. This
// includes setting the frame sizes. This approach found at http://stackoverflow.com/a/11218097/264775
emptyBulb = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"Light.png"]];
transBulb = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"Light-moving.png"]];
solidBulb = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"Light-on.png"]];

[emptyBulb setFrame:CGRectMake(10, BULB_TOP, 300, BULB_HEIGHT)]; // 298 x 280
[transBulb setFrame:CGRectMake(10, BULB_TOP, 300, BULB_HEIGHT)]; // 298 x 280
[solidBulb setFrame:CGRectMake(10, BULB_TOP, 300, BULB_HEIGHT)]; // 298 x 280

[self.view addSubview:solidBulb]; // Empty on top, then trans, then solid.
[self.view addSubview:transBulb];
[self.view addSubview:emptyBulb];

// Create a mask for the empty layer so it will cover the other layers.
emptyMask = [CALayer layer];
[emptyMask setContentsScale:emptyBulb.layer.contentsScale]; // handle retina scaling
[emptyMask setFrame:emptyBulb.layer.bounds];
[emptyMask setBackgroundColor:[UIColor blackColor].CGColor];
emptyBulb.layer.mask = emptyMask;

// Also create a mask for the transparent image.
transMask = [CALayer layer];
[transMask setContentsScale:transBulb.layer.contentsScale]; // handle retina scaling
[transMask setFrame:transBulb.layer.bounds];
[transMask setBackgroundColor:[UIColor blackColor].CGColor];
transBulb.layer.mask = transMask;

Answer 1

刚刚通过this answer 找到了解决方案。如果您查看文档的右侧部分，您会发现以下内容：

- (id)presentationLayer

返回包含当前事务开始时所有属性的图层副本，并应用任何活动动画。

因此，如果我在第一次检查透明蒙版位置（也称为实体级别）之前添加此代码，我会抓取当前动画位置并可以在填充和填充之间切换。

CALayer *temp;

if (transMask.animationKeys.count > 0) {
    temp = transMask.presentationLayer;
    transMask.position = temp.position;
}

if (emptyMask.animationKeys.count > 0) {
    temp = emptyMask.presentationLayer;
    emptyMask.position = temp.position;
}

Answer 2

layer.presentation() 每次获取原始图层时都会对其进行复制，并且您需要为您拥有的每个自定义 CALayer 覆盖 init(layer: Any)。

另一种从当前状态开始的可能方法是使用当前动画的 beginTime 设置动画的 beginTime。它允许使用偏移量开始新的动画。

在你的情况下，它可能是（Swift）：

if let currentAnimation = slider.animation(forKey: "colorize") {
    let currentTime = CACurrentMediaTime()
    let animationElapsedTime = currentAnimation.beginTime + currentAnimation.duration - currentTime
    a.beginTime = currentTime - animationElapsedTime
}

不过，这对于线性时序非常有效，但对于其他时序，可能很难计算出正确的时间。