objective-c - 具有贝塞尔曲线和恒定速度的 CAKeyframeAnimation

Question

我正在尝试沿包含一些贝塞尔曲线的 CGPathRef 制作图形动画，我希望动画从开始到结束具有平滑、恒定的速度。不过，我遇到的是每次到达关键点时动画都会缓入缓出。我试过使用不同的 timingFunction 和 calculationMode 设置，但我似乎无法找到正确的组合来完成工作。

这是我到目前为止所得到的:

-(void)animate
{
  CAKeyframeAnimation *posAnim = [CAKeyframeAnimation animationWithKeyPath:@"position"];
  posAnim.path = [self pathForAnimation];
  posAnim.duration = 12.0;
  posAnim.calculationMode = kCAAnimationPaced;
  posAnim.fillMode = kCAFillModeBoth;
  posAnim.removedOnCompletion = NO;
  posAnim.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
  [image.layer addAnimation:posAnim forKey:@"posAnim"];
}

-(CGPathRef)pathForAnimation
{
  CGMutablePathRef path;
  CGPoint point;
  CGPoint controlPoint1;
  CGPoint controlPoint2;

  path = CGPathCreateMutable();
  point = CGPointMake(209.5f, 24.5f);
  CGPathMoveToPoint(path, NULL, point.x, point.y);

  point = CGPointMake(249.5f, 64.5f);
  controlPoint1 = CGPointMake(232.5f, 25.5f);
  controlPoint2 = CGPointMake(249.5f, 37.5f);
  CGPathAddCurveToPoint(path, NULL, controlPoint1.x, controlPoint1.y, controlPoint2.x, controlPoint2.y, point.x, point.y);

  point = CGPointMake(146.5f, 301.5f);
  controlPoint1 = CGPointMake(249.5f, 91.5f);
  controlPoint2 = CGPointMake(147.5f, 258.5f);
  CGPathAddCurveToPoint(path, NULL, controlPoint1.x, controlPoint1.y, controlPoint2.x, controlPoint2.y, point.x, point.y);

  point = CGPointMake(146.5f, 458.5f);
  controlPoint1 = CGPointMake(145.5f, 344.5f);
  controlPoint2 = CGPointMake(170.5f, 418.5f);
  CGPathAddCurveToPoint(path, NULL, controlPoint1.x, controlPoint1.y, controlPoint2.x, controlPoint2.y, point.x, point.y);

  point = CGPointMake(18.5f, 530.5f);
  controlPoint1 = CGPointMake(122.5f, 498.5f);
  controlPoint2 = CGPointMake(18.5f, 530.5f);
  CGPathAddCurveToPoint(path, NULL, controlPoint1.x, controlPoint1.y, controlPoint2.x, controlPoint2.y, point.x, point.y);

  return path;
}

为了它的值(value)，我尝试用直线替换曲线(使用 CGPathAddLineToPoint)，这给了我想要的恒定速度。但当然，如果可能的话，我宁愿有曲线。

我也曾尝试用 timingFunctions 数组替换 timingFunction，但无济于事。

Answer 1

您是否尝试过将关键帧动画的 calculationMode 属性设置为 kCAAnimationCubicPaced？该属性专门用于使动画在整个曲线上遵循恒定的速度。