Windows 8 Store App：使用固定比率进行图像裁剪

Question

我在微软的Windows 8应用程序上遇到了这个针对图像裁剪的解决方案，但我需要强制用户裁剪到特定比例（例如1：1,4：3），请建议/或任何有更好的解决方案吗？

非常感谢你。

这是解决方案（该解决方案允许用户在x，y上自由裁剪） http://code.msdn.microsoft.com/windowsapps/CSWin8AppCropBitmap-52fa1ad7/sourcecode?fileId=70609&pathId=1727496808

http://code.msdn.microsoft.com/windowsapps/CSWin8AppCropBitmap-52fa1ad7

/// <summary> 
    /// If a pointer which is captured by the corner moves，the select region will be updated. 
    /// </summary> 
    void Corner_PointerMoved(object sender, PointerRoutedEventArgs e) 
    { 

        Windows.UI.Input.PointerPoint pt = e.GetCurrentPoint(this); 
        uint ptrId = pt.PointerId; 

        if (pointerPositionHistory.ContainsKey(ptrId) && pointerPositionHistory[ptrId].HasValue) 
        { 
            Point currentPosition = pt.Position; 
            Point previousPosition = pointerPositionHistory[ptrId].Value; 

            double xUpdate = currentPosition.X - previousPosition.X; 
            double yUpdate = currentPosition.Y - previousPosition.Y; 

            this.selectedRegion.UpdateCorner((sender as ContentControl).Tag as string, xUpdate, yUpdate); 

            pointerPositionHistory[ptrId] = currentPosition; 
        } 

        e.Handled = true; 
    }