SpriteKit 实现 COC 游戏场景的平移和缩放

继承SKSpriteNode，重写touches逻辑，可实现类似COC游戏场景的平移和缩放。

代码如下：

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{    if (1 == touches.count) {        UITouch *touch = [touches anyObject];        CGPoint currentPoint = [touch locationInNode:self.parent];        CGPoint previousPoint = [touch previousLocationInNode:self.parent];        CGPoint translation = CGPointMake(currentPoint.x - previousPoint.x, currentPoint.y - previousPoint.y);        [self handlePanTranslation:translation];    } else if (2 == touches.count) {        NSArray *arr = [touches allObjects];        UITouch *touch1 = [arr objectAtIndex:0];        UITouch *touch2 = [arr objectAtIndex:1];        CGPoint position1 = [touch1 locationInNode:self];        CGPoint position2 = [touch2 locationInNode:self];        CGPoint previousPosition1 = [touch1 previousLocationInNode:self];        CGPoint previousPosition2 = [touch2 previousLocationInNode:self];                // calculate pinch rate and execute pinch        CGFloat distance = WLDistanceBetweenPoints(position1, position2);        CGFloat preDistance = WLDistanceBetweenPoints(previousPosition1, previousPosition2);                CGFloat rate = self.currentRate + (distance - preDistance) / preDistance;        CGFloat minWidth = self.scene.size.width;        CGFloat minHeight = self.scene.size.height;        CGFloat minWidthRate = minWidth / 1280.f;        CGFloat minHeightRate = minHeight / 656.f;        rate = MIN(rate, 1.5);        rate = MAX(rate, minWidthRate);        rate = MAX(rate, minHeightRate);                CGSize beforeSize = self.size;        self.xScale = rate;        self.yScale = rate;        CGSize afterSize = self.size;                self.currentRate = rate;                // garuntee edge from out of screen        CGFloat xDelta = (afterSize.width - beforeSize.width) / 2;        CGFloat yDelta = (afterSize.height - beforeSize.height) / 2;        CGPoint currentPosition = self.position;        currentPosition.x -= xDelta;        currentPosition.y -= yDelta;        currentPosition.x = MIN(currentPosition.x, 0);        currentPosition.x = MAX(currentPosition.x, self.scene.size.width - self.size.width);        currentPosition.y = MIN(currentPosition.y, 0);        currentPosition.y = MAX(currentPosition.y, self.scene.size.height - self.size.height);        self.position = currentPosition;    }}