在可可触摸中实现基于触摸的旋转

问题描述：

我想知道什么是在我的iPhone应用程序中实现基于旋转的拖拽动作的最佳方式。在可可触摸中实现基于触摸的旋转

我有一个UIView，我希望围绕它的中心旋转，当用户手指触摸视图并移动它时。把它想象成需要用手指调整的刻度盘。

的基本问题归结为：

1）我应该还记得最初的角度，改造时的touchesBegan被调用，然后每touchesMoved被调用时应用新的变换，基于当前位置的看法手指，例如，像：

- (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. 
}

2）如果我只是记得我最后已知的位置/角度和旋转基于对之间的角度差的观点，现在，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; 
    }

第二个选项对我更有意义，但它没有给出令人愉快的结果（锯齿更新和非平滑旋转）。在性能方面哪种方式最好（如果有的话）？

干杯！

答

您考虑过使用UIRotationGestureRecognizer吗？看起来好像已经有了逻辑，可能会让事情变得更简单。

虽然UIGestureRecognizers是很好用，它们确实有一个缺点：它通常需要大约10个像素直到他们认出他们的手势。我发现在我的一个与图形相关的应用程序中是不可接受的，所以我以老式的方式来做。如果你想识别多个手势，它会变得更加棘手。知道如何绘制状态图有助于很多... – 2011-04-18 20:29:05

答

它实际上比您尝试的更简单。

您需要三个数据点：

你的观点的由来。
当前触摸
之前的触摸

传递给你的触摸对象实际上包含了最后触摸位置的位置的位置。所以你不需要跟踪它。

所有你需要做的就是两条线之间计算角度：

产地为当前触摸
原产于之前的触摸

然后将其转换成弧度，并使用你的CGAffineTransformRotate（）。在touchesMoved处理程序中完成所有操作。

这里是计算你需要的只是什么功能：

杰夫拉马什的

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;  
}

礼貌：

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

例子：

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

在可可触摸中实现基于触摸的旋转

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