Question

我现有代码用于跟踪多点触控位置，然后移动，旋转和缩放项目 - 在这种情况下是图像 - 适当。

代码工作得很好，本身就很完美，但是对于这个特殊的任务，我只需要移动和旋转。我花时间试图弄清楚这个例程中发生了什么，但数学不是我的强项，所以想看看是否有人可以提供帮助？

- (CGAffineTransform)incrementalTransformWithTouches:(NSSet *)touches
{
    NSArray *sortedTouches = [[touches allObjects] sortedArrayUsingSelector:@selector(compareAddress:)];
    NSInteger numTouches = [sortedTouches count];

 // No touches
 if (numTouches == 0) {
        return CGAffineTransformIdentity;
    }

 // Single touch
 if (numTouches == 1) {
        UITouch *touch = [sortedTouches objectAtIndex:0];
        CGPoint beginPoint = *(CGPoint *)CFDictionaryGetValue(touchBeginPoints, touch);
        CGPoint currentPoint = [touch locationInView:self.superview];
  return CGAffineTransformMakeTranslation(currentPoint.x - beginPoint.x, currentPoint.y - beginPoint.y);
 }

 // If two or more touches, go with the first two (sorted by address)
 UITouch *touch1 = [sortedTouches objectAtIndex:0];
 UITouch *touch2 = [sortedTouches objectAtIndex:1];

    CGPoint beginPoint1 = *(CGPoint *)CFDictionaryGetValue(touchBeginPoints, touch1);
    CGPoint currentPoint1 = [touch1 locationInView:self.superview];
    CGPoint beginPoint2 = *(CGPoint *)CFDictionaryGetValue(touchBeginPoints, touch2);
    CGPoint currentPoint2 = [touch2 locationInView:self.superview];

 double layerX = self.center.x;
 double layerY = self.center.y;

 double x1 = beginPoint1.x - layerX;
 double y1 = beginPoint1.y - layerY;
 double x2 = beginPoint2.x - layerX;
 double y2 = beginPoint2.y - layerY;
 double x3 = currentPoint1.x - layerX;
 double y3 = currentPoint1.y - layerY;
 double x4 = currentPoint2.x - layerX;
 double y4 = currentPoint2.y - layerY;

 // Solve the system:
 //   [a b t1, -b a t2, 0 0 1] * [x1, y1, 1] = [x3, y3, 1]
 //   [a b t1, -b a t2, 0 0 1] * [x2, y2, 1] = [x4, y4, 1]

 double D = (y1-y2)*(y1-y2) + (x1-x2)*(x1-x2);
 if (D < 0.1) {
        return CGAffineTransformMakeTranslation(x3-x1, y3-y1);
    }

 double a = (y1-y2)*(y3-y4) + (x1-x2)*(x3-x4);
 double b = (y1-y2)*(x3-x4) - (x1-x2)*(y3-y4);
 double tx = (y1*x2 - x1*y2)*(y4-y3) - (x1*x2 + y1*y2)*(x3+x4) + x3*(y2*y2 + x2*x2) + x4*(y1*y1 + x1*x1);
 double ty = (x1*x2 + y1*y2)*(-y4-y3) + (y1*x2 - x1*y2)*(x3-x4) + y3*(y2*y2 + x2*x2) + y4*(y1*y1 + x1*x1);

 return CGAffineTransformMake(a/D, -b/D, b/D, a/D, tx/D, ty/D);
}

我试图阅读矩阵的工作方式，但无法完全理解。更可能是问题的是计算，正如我所提到的那样，这不是我的强项。

我从这个例程中需要的是一个执行我的移动和旋转但忽略比例的变换 - 因此忽略了2个手指触摸点之间的距离，并且缩放不受影响。

我已经看过互联网上的其他例程来处理多点触控旋转，但我尝试的所有例程都有某些方面的问题（平滑，抬手时跳跃等），而上面的代码是移动点，缩放和旋转动作。

任何帮助表示赞赏！

Answer 1

做这样的事情：

CGAffineTransform transform = self.view.transform;
float scale = sqrt(transform.a*transform.a + transform.c*transform.c);
self.view.transform = CGAffineTransformScale(transform, 1/scale, 1/scale);

在touchesMoved：withEvent：和updateOriginalTransformForTouches方法结束时。基本上，您计算当前比例值，然后将转换矩阵与反转比例值相乘。

iPhone多点触控移动，缩放和旋转，如何防止缩放？

1 个答案: