动画点多次,更自然

Question

所以我当前的版本看起来像这样:动画电影

我对核心动画很新,所以我试图实现的是有多个点,比如当前的一个,从左侧框中以各种角度,高度和速度移出它,就像一个网球机.

第一个问题是,我的"球"看起来不像是从重力中被抓住了,而且最初的速度还不够快.

另外,如何通过开始之间的距离变化多次执行此动画.

如果有什么不清楚,请发表评论.

我目前的代码:

- (void)loadView {
    [super loadView];

    self.view.backgroundColor = [UIColor lightGrayColor];   

    CGPoint startPoint = CGPointMake(20, 300);
    CGPoint endPoint = CGPointMake(300, 500);

    UIBezierPath *trackPath = [UIBezierPath bezierPath];
    [trackPath moveToPoint:startPoint];
    [trackPath addQuadCurveToPoint:endPoint controlPoint:CGPointMake(endPoint.x, startPoint.y)];

    CALayer *point = [CALayer layer];
    point.bounds = CGRectMake(0, 0, 20.0, 20.0);
    point.position = startPoint;
    point.contents = (id)([UIImage imageNamed:@"point.png"].CGImage);
    [self.view.layer addSublayer:point];

    CAKeyframeAnimation *anim = [CAKeyframeAnimation animationWithKeyPath:@"position"];
    anim.path = trackPath.CGPath;
    anim.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut];
    anim.repeatCount = HUGE_VALF;
    anim.duration = 2.0;
    [point addAnimation:anim forKey:@"movepoint"];

    CALayer *caseLayer = [CALayer layer];
    caseLayer.bounds = CGRectMake(0, 0, 140.0, 150.0);
    caseLayer.position = startPoint;
    caseLayer.contents = (id)([UIImage imageNamed:@"case.png"].CGImage);
    [self.view.layer addSublayer:caseLayer];

}

Answer 1

模拟重力的最简单方法是使用您在基础物理中学到的抛物线方程。简而言之，下面的函数采用初始位置、速度和角度（以弧度为单位，其中 0 位于右侧）。CALayer 出现在该位置并以该速度和角度进行射击。

我正在使用 CADisplayLink（实际上是一个与帧速率同步的计时器）来非常快速地调用函数。每次调用该函数时，该点都会移动。水平速度是恒定的，垂直速度每帧向底部增加以模拟重力（`vy -= 0.5f;）。如果你想要更多/更少的重力，只需调整这个 0.5f 值即可。

- (id)initWithFrame:(CGRect)frame {

    self = [super initWithFrame:frame];
    if (self) {
      point = [[CALayer alloc] init];
      point.bounds = CGRectMake(0.0f, 0.0f, 10.0f, 10.0f);
      point.backgroundColor = [UIColor redColor].CGColor;
      point.position = CGPointMake(-10.0f, -10.0f);
      [self.layer addSublayer:point];
      [point release];
    }
    return self;
}

-(void)animateBallFrom:(CGPoint)start withSpeed:(CGFloat)speed andAngle:(CGFloat)angle       
  vx = speed*cos(angle);
  vy = speed*sin(angle);


  [CATransaction begin];
  [CATransaction setDisableActions:YES];
  point.position = start;
  [CATransaction commit];

  displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(animate)];
  [displayLink setFrameInterval:2];
  [displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
}

-(void)animate {
  if (point.position.x + point.bounds.size.width/2.0f < 0.0f || point.position.x > self.bounds.size.width + point.bounds.size.width/2.0f ||
    point.position.y + point.bounds.size.height/2.0f < 0.0f || point.position.y > self.bounds.size.height + point.bounds.size.height/2.0f) {
    [displayLink invalidate];
  } else {
    [CATransaction begin];
    [CATransaction setDisableActions:YES];
    point.position = CGPointMake(point.position.x+vx, point.position.y-vy);
    vy -= 0.5f;
    [CATransaction commit];
  }
}

和界面：

@interface Bounce : UIView {
  CALayer *point;
  CADisplayLink *displayLink;
  CGFloat vx, vy;
}

-(void)animateBallFrom:(CGPoint)start withSpeed:(CGFloat)speed andAngle:(CGFloat)angle;

@end