位图图像：纵向裁剪

Question

为我的应用添加相机功能正在扼杀我！从基本的UWP相机样本开始，但我必须添加缩放功能，在预览控件周围添加ScrollViewer并使我的生活变得复杂。在不同的样本中找到了裁剪代码。一切都在横向上工作，但当您将平板电脑旋转为肖像时，裁剪后的图像（即使没有任何实际裁剪）也会旋转90度。

裁剪逻辑采用originX / Y，ScrollViewer.ViewportWidth / Height＆amp; ScrollViewer.ExtentWidth /高度。我不明白这些值如何随着旋转而变化！在Landscape中我使用topLeft作为X / Y.我会为肖像做什么？我将宽度设置为400，在两个视图中它都是STILL 400，所以我不相信应该翻转宽度/高度。

这是裁剪代码。任何人都可以评论2（实际上是4个）方向应该有什么不同吗？

       async public static Task<WriteableBitmap> GetCroppedBitmapAsync(StorageFile originalImageFile,
                                                 Point startPoint, Size cropSize, Size previewSize)
    {
        using (IRandomAccessStream stream = await originalImageFile.OpenReadAsync())
        {
            // Create a decoder from the stream. With the decoder, we can get the properties of the image.
            BitmapDecoder decoder = await BitmapDecoder.CreateAsync(stream);

            // Adjust the start x/y to the stream size 
            uint scaledStartPointX = (uint)Math.Round((decoder.PixelWidth * (startPoint.X / previewSize.Width)));
            uint scaledStartPointY = (uint)Math.Round((decoder.PixelHeight * (startPoint.Y / previewSize.Height)));

            // Now get the scaled size of the viewport (ie the cropped area)
            uint selectedAreaWidth = (uint)Math.Round(decoder.PixelWidth * (cropSize.Width / previewSize.Width));
            uint selectedAreaHeight = (uint)Math.Round(decoder.PixelHeight * (cropSize.Height / previewSize.Height));

            // Get the cropped pixels.
            byte[] pixels = await GetPixelData(decoder, scaledStartPointX, scaledStartPointY, selectedAreaWidth, selectedAreaHeight,
                decoder.PixelWidth, decoder.PixelHeight);

            // Stream the bytes into a WriteableBitmap
            WriteableBitmap cropBmp = new WriteableBitmap((int)selectedAreaWidth, (int)selectedAreaHeight);
            Stream pixStream = cropBmp.PixelBuffer.AsStream();
            pixStream.Write(pixels, 0, (int)(selectedAreaWidth * selectedAreaHeight * 4));

            return cropBmp;
        }

    }