在 cocoa touch 中实现基于触摸的旋转

Question

我想知道在我的 iPhone 应用程序中实现基于旋转的拖动运动的最佳方法是什么。

我有一个 UIView，当用户手指触摸视图并移动它时，我希望围绕其中心旋转。把它想象成一个需要用手指调节的表盘。

基本问题归结为：

1）我是否应该记住调用touchesBegan时的初始角度和变换，然后每次调用touchesMoved时根据手指的当前位置对视图应用新的变换，例如：

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

  UITouch *touch = [touches anyObject];
  CGPoint currentPoint = [touch locationInView:self]; //current position of touch   

 if (([touch view] == self) 
    &&  [Utility getDistance:currentPoint toPoint:self.middle] <= ROTATE_RADIUS //middle is centre of view
    && [Utility getDistance:currentPoint toPoint:self.middle] >= MOVE_RADIUS) { //will be rotation gesture

  //remember state of view at beginning of touch
  CGPoint top = CGPointMake(self.middle.x, 0);
  self.initialTouch = currentPoint;
  self.initialAngle = angleBetweenLines(self.middle, top, self.middle, currentPoint);   
  self.initialTransform = self.transform;
 }
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{

  UITouch *touch = [touches anyObject];
  CGPoint currentPoint = [touch locationInView:self]; //current position of touch

  if (([touch view] == self) 
  &&  [Utility getDistance:currentPoint toPoint:self.middle] <= ROTATE_RADIUS
  && [Utility getDistance:currentPoint toPoint:self.middle] >= MOVE_RADIUS) { //a rotation gesture

  //rotate tile
  float newAngle = angleBetweenLines(self.middle, CGPointMake(self.middle.x, 0), self.middle, currentPoint); //touch angle
  float angleDif = newAngle - self.initialAngle; //work out dif between angle at beginning of touch and now.
  CGAffineTransform newTransform = CGAffineTransformRotate(self.initialTransform, angleDif); //create new transform
  self.transform = newTransform;  //apply transform.
}

或者

2）我是否应该简单地记住最后一个已知的位置/角度，并根据该位置/角度与现在之间的角度差异旋转视图，例如：

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

      UITouch *touch = [touches anyObject];
      CGPoint currentPoint = [touch locationInView:self]; //current position of touch   

     if (([touch view] == self) 
        &&  [Utility getDistance:currentPoint toPoint:self.middle] <= ROTATE_RADIUS
        && [Utility getDistance:currentPoint toPoint:self.middle] >= MOVE_RADIUS) { //will be rotation gesture

      //remember state of view at beginning of touch
      CGPoint top = CGPointMake(self.middle.x, 0);
      self.lastTouch = currentPoint;
      self.lastAngle = angleBetweenLines(self.middle, top, self.middle, currentPoint);  
     }
    }

    - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{

      UITouch *touch = [touches anyObject];
      CGPoint currentPoint = [touch locationInView:self]; //current position of touch

      if (([touch view] == self) 
      &&  [Utility getDistance:currentPoint toPoint:middle] <= ROTATE_RADIUS
      && [Utility getDistance:currentPoint toPoint:middle] >= MOVE_RADIUS) { //a rotation gesture

      //rotate tile
      float newAngle = angleBetweenLines(self.middle, CGPointMake(self.middle.x, 0), self.middle, currentPoint); //touch angle
      float angleDif = newAngle - self.lastAngle; //work out dif between angle at beginning of touch and now.
      CGAffineTransform newTransform = CGAffineTransformRotate(self.transform, angleDif); //create new transform

      self.transform = newTransform;  //apply transform.
      self.lastTouch = currentPoint;
      self.lastAngle = newAngle;
    }

第二个选项对我来说更有意义，但它并没有给出非常令人满意的结果（锯齿状更新和不平滑旋转）。就性能而言，哪种方法最好（如果有）？

干杯!

Answer 1

它实际上比您尝试过的要简单得多。

您需要三个数据点：

• 您的观点的起源。
• 当前触摸的位置 上
• 一次触摸的位置

传递给您的 Touch 对象实际上包含最后一次触摸的位置。所以你不需要跟踪它。

您所要做的就是计算两条线之间的角度：

• 原点到当前触摸
• 原点到上一次触摸

然后将其转换为弧度并在 CGAffineTransformRotate() 中使用它。在你的 TouchMoved 处理程序中完成这一切。

这是一个计算您需要的函数：

static inline CGFloat angleBetweenLinesInRadians(CGPoint line1Start, CGPoint line1End, CGPoint line2Start, CGPoint line2End) {

    CGFloat a = line1End.x - line1Start.x;
    CGFloat b = line1End.y - line1Start.y;
    CGFloat c = line2End.x - line2Start.x;
    CGFloat d = line2End.y - line2Start.y;

    CGFloat line1Slope = (line1End.y - line1Start.y) / (line1End.x - line1Start.x);
    CGFloat line2Slope = (line2End.y - line2Start.y) / (line2End.x - line2Start.x);

    CGFloat degs = acosf(((a*c) + (b*d)) / ((sqrt(a*a + b*b)) * (sqrt(c*c + d*d))));


    return (line2Slope > line1Slope) ? degs : -degs;    
}

由 Jeff LaMarche 提供：

http://iphonedevelopment.blogspot.com/2009/12/better-two-finger-rotate-gesture.html

示例：

UITouch *touch = [touches anyObject];
CGPoint origin = [view center];
CGFloat angle = angleBetweenLinesInRadians(origin, [touch previousLocationInView:self.superview.superview], origin, [touch locationInView:self.superview.superview]);

Answer 2

您是否考虑过使用UIRotationGestureRecognizer？似乎逻辑已经融入其中，并且可能会让事情变得更简单。