UWP 裁切 SoftwareBitmap

  //设置源图ImageSource为WriteableBitmap类型
            BitmapImage himage = this.imageTarget2.Source as BitmapImage;

            RandomAccessStreamReference random = RandomAccessStreamReference.CreateFromUri(himage.UriSource);

            using (IRandomAccessStream stream = await random.OpenReadAsync())
            {
                stream.Seek();
                BitmapDecoder decoder = await BitmapDecoder.CreateAsync(stream);
                BitmapFrame bitmapFrame = await decoder.GetFrameAsync();
                // Get the pixels
                var transform = new BitmapTransform { ScaledWidth = decoder.PixelWidth, ScaledHeight = decoder.PixelHeight };
                PixelDataProvider dataProvider =
                    await bitmapFrame.GetPixelDataAsync(BitmapPixelFormat.Bgra8,
                        BitmapAlphaMode.Straight,
                        transform,
                        ExifOrientationMode.RespectExifOrientation,
                        ColorManagementMode.ColorManageToSRgb);

                var image_array = dataProvider.DetachPixelData();
                var image_array_width = (int)decoder.PixelWidth;
                var image_array_height = (int)decoder.PixelHeight;
                var writeableBitmap = new WriteableBitmap(image_array_width, image_array_height);
                stream.Seek();
                await writeableBitmap.SetSourceAsync(stream);
                this.imageSource1.Source = writeableBitmap;//WriteableBitmap 类型很重要
            }

  //裁切方法
        public async static Task<SoftwareBitmap> GetCroppedBitmapAsync(SoftwareBitmap softwareBitmap, uint x, uint y, uint width, uint height)
        {
            using (InMemoryRandomAccessStream stream = new InMemoryRandomAccessStream())
            {
                BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.BmpEncoderId, stream);

                encoder.SetSoftwareBitmap(softwareBitmap);

                encoder.BitmapTransform.Bounds = new BitmapBounds()
                {
                    X = x,
                    Y = y,
                    Height = height,
                    Width = width
                };

                await encoder.FlushAsync();

                BitmapDecoder decoder = await BitmapDecoder.CreateAsync(stream);

                return await decoder.GetSoftwareBitmapAsync(softwareBitmap.BitmapPixelFormat, softwareBitmap.BitmapAlphaMode);
            }
        }

            //实例:
            WriteableBitmap wb = this.imageSource1.Source as WriteableBitmap; ;
            SoftwareBitmap sb = new SoftwareBitmap(BitmapPixelFormat.Bgra8, wb.PixelWidth, wb.PixelHeight);
            sb.CopyFromBuffer(wb.PixelBuffer);//WriteableBitmap转为SoftwareBitmap
            var sbmp = await GetCroppedBitmapAsync(sb, 0, 50, 100, 100);//调用裁切方法
            WriteableBitmap writeableBitmap = new WriteableBitmap(sbmp.PixelWidth, sbmp.PixelHeight);
            sbmp.CopyToBuffer(writeableBitmap.PixelBuffer);//SoftwareBitmap转为WriteableBitmap
            this.imageTarget2.Source = writeableBitmap;//设置目标图ImageSource为WriteableBitmap类型