在夹点期间限制平移以缩放iOS

在我的应用程序中,我已经实现了缩放和平移。缩放和平移都有效,但我想限制平移,以便缩放图像的边缘不能拖到视图中留下空白。

不同比例因子的坐标范围似乎不是线性的。例如,在具有764x764图像视图的iPad上,在2x变焦下,全平移的变换X坐标范围是-191到191。在3倍,范围大约是-254到254。

所以我的问题是,如何计算给定比例因子的泛极限?

这是我的手势识别器代码:

@interface myVC()
{
  CGPoint ptPanZoom1;
  CGPoint ptPanZoom2;
  CGFloat fltScale;
}
@property (nonatomic, strong) UIImageView* imgView; // View hosting pan/zoom image
@end

- (IBAction) handlePan:(UIPanGestureRecognizer*) sender
{
  if ( sender.state == UIGestureRecognizerStateBegan )
  {
    ptPanZoom2 = ptPanZoom1;
    return;
  }

  if ( (sender.state == UIGestureRecognizerStateChanged)
    || (sender.state == UIGestureRecognizerStateEnded) )
  {
    CGPoint ptTrans = [sender translationInView:self.imgView];

    ptPanZoom1.x = ptTrans.x + ptPanZoom2.x;
    ptPanZoom1.y = ptTrans.y + ptPanZoom2.y;

    CGAffineTransform trnsFrm1 = CGAffineTransformMakeTranslation(ptPanZoom1.x, ptPanZoom1.y);
    CGAffineTransform trnsFrm2 = CGAffineTransformMakeScale(fltScale, fltScale);
    self.imgView.transform = CGAffineTransformConcat(trnsFrm1, trnsFrm2);
  }
}

- (IBAction) handlePinch:(UIPinchGestureRecognizer*) sender
{
  if ( (sender.state == UIGestureRecognizerStateBegan)
    || (sender.state == UIGestureRecognizerStateChanged)
    || (sender.state == UIGestureRecognizerStateEnded) )
  {
    fltScale *= sender.scale;
    sender.scale = 1.0;

    if ( fltScale <= 1.0 )
    {
      fltScale = 1.0;
      ptPanZoom1.x  = 0.0; // When scale goes to 1, snap position back
      ptPanZoom1.y  = 0.0;
    }
    else if ( fltScale > 6.0 )
    {
      fltScale = 6.0;
    }

    CGAffineTransform trnsFrm1 = CGAffineTransformMakeTranslation(ptPanZoom1.x, ptPanZoom1.y);
    CGAffineTransform trnsFrm2 = CGAffineTransformMakeScale(fltScale, fltScale);
    self.imgView.transform = CGAffineTransformConcat(trnsFrm1, trnsFrm2);
  }
}