WPF 大图片平移拖动边界定义问题

[E次奥]

最近在实现一个类似QQ图片查看器的东西，遇到一些问题，求各位帮忙；

图片用的变换缩放改变显示大小， 放大后，如何拖动才能让图片的边界不能进入窗体内部？

[exception92]

描述过于简单，代码+贴图。

[jack_z63]

废话不说，直接看下面代码：
private void Domousemove(Rectangle img, MouseEventArgs e)
{
if (e.LeftButton != MouseButtonState.Pressed)
{
return;
}
TransformGroup group = grid1.FindResource("Imageview") as TransformGroup;

TranslateTransform transform = group.Children[1] as TranslateTransform;
Point position = e.GetPosition(img);

var transform0 = group.Children[0] as ScaleTransform;
double xScale = transform0.ScaleX; //取出放大系数

double parentH = img.ActualHeight; //容器控件高
double parentW = img.ActualWidth; //容器控件宽
double yCount = parentH * yScale; //当前图像高
double xCount = parentW * xScale; //当前图像宽
double xRight = parentW - xCount; //容器与图像宽的差
double yBottom = parentH - yCount; //容器与图像高的差
double diffX = position.X - mouseXY.X; //当前申请的平移X分量
double diffY = position.Y - mouseXY.Y; //当前申请的平移Y分量
if (((transform.X + diffX) < xRight) || ((transform.Y + diffY) < yBottom) || ((transform.X + diffX) > 0) ||
((transform.Y + diffY) > 0))
{ //如果申请平移量使图像边界进入容器内则不执行平移
transform.X += 0;
transform.Y += 0;
}
else
{
transform.X += diffX; // m_PreviousMousePoint.X;
transform.Y += diffY; // m_PreviousMousePoint.Y;
}
mouseXY = position;

}