如何将图像从SharpDX/Direct2D复制到.NET位图

我开发了一个.NETWinForms应用程序，需要缩放许多大图像，并将它们显示为表单上的小图标。我对性能有问题，特别是在特定的机器上。因此，我现在的目标是使用SharpDX使用Direct2D缩放这些图像。不知何故，现在图像被缩放了，但我无法将图像从DirectX位图复制到.NET位图

Private Sub CopyBitmapFromDxToGDI(bitmap As d2.Bitmap1, bmp As Drawing.Bitmap)
   Dim d2dBitmapProps2 = New d2.BitmapProperties1(d2PixelFormat, 96, 96, BitmapOptions.CpuRead Or BitmapOptions.CannotDraw  )
   Dim d2dRenderTarget2 = New d2.Bitmap1(d2dContext, New Size2(bmp.Width, bmp.Height), d2dBitmapProps2)
   d2dRenderTarget2.CopyFromRenderTarget(d2dContext)
   Dim surface = d2dRenderTarget2.Surface
   Dim dataStream As DataStream = Nothing
   surface.Map(dxgi.MapFlags.Read, dataStream)
   Dim bmpData As System.Drawing.Imaging.BitmapData = bmp.LockBits(
      New System.Drawing.Rectangle(0, 0, bmp.Width, bmp.Height),
      System.Drawing.Imaging.ImageLockMode.ReadWrite,
      System.Drawing.Imaging.PixelFormat.Format32bppPArgb)

   Dim offset = 3
   Debug.WriteLine($"({surface.Description.Width}, {surface.Description.Height})")
   For y As Integer = 0 To surface.Description.Height - 1         
      For x As Integer = 0 To surface.Description.Width -1         
         Dim b As Byte = dataStream.Read(Of Byte)()
         Dim g As Byte = dataStream.Read(Of Byte)()
         Dim r As Byte = dataStream.Read(Of Byte)()
         Dim a As Byte = dataStream.Read(Of Byte)()            

         Marshal.WriteByte(bmpData.Scan0, offset, a)
         offset += 1
         Marshal.WriteByte(bmpData.Scan0, offset, r)
         offset += 1
         Marshal.WriteByte(bmpData.Scan0, offset, g)
         offset += 1
         Marshal.WriteByte(bmpData.Scan0, offset, b)
         offset += 1
      Next
   Next
   bmp.UnlockBits(bmpData)
   surface.Unmap()
End Sub

代码相当简单。我创建了一个允许CPU访问的新位图，从中获取数据流，然后逐字节将数据写入.NET位图。然而，这段代码大多不起作用。仅当目标图像具有特定大小时，它才能正确渲染图像。对于特定的大小，它只会因AccessViolationException而崩溃。对于特定的大小，它被渲染为奇怪：

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你知道我在代码中遗漏了什么吗？

要解决这个问题，需要使用dataRectangle.Pitch计算内存流中每个像素的位置。以下代码现在可以正常工作：

Private Sub CopyBitmapFromDxToGDI(bitmap As d2.Bitmap1, bmp As Drawing.Bitmap)
   Dim d2TempBitmapProps = New d2.BitmapProperties1(d2PixelFormat, 96, 96, BitmapOptions.CpuRead Or BitmapOptions.CannotDraw)
   Dim d2TempBitmap = New d2.Bitmap1(d2dContext, New Size2(bmp.Width, bmp.Height), d2TempBitmapProps)      
   d2TempBitmap.CopyFromRenderTarget(d2dContext)

   Dim surface = d2TempBitmap.Surface
   Dim dataStream As DataStream = Nothing
   Dim dataRectangle As DataRectangle = surface.Map(dxgi.MapFlags.Read, dataStream)
   Dim bmpData As Imaging.BitmapData = bmp.LockBits(New Drawing.Rectangle(0, 0, bmp.Width, bmp.Height), Imaging.ImageLockMode.ReadWrite, Imaging.PixelFormat.Format32bppPArgb)

   Dim offset = bmpData.Reserved
   Dim buffer(4) As Byte
   For y As Integer = 0 To surface.Description.Height - 1
      For x As Integer = 0 To surface.Description.Width - 1

         dataStream.Seek((y * dataRectangle.Pitch) + (x * 4), SeekOrigin.Begin)
         dataStream.Read(buffer, 0, 4)           

         Marshal.WriteByte(bmpData.Scan0, offset, buffer(3))            
         Marshal.WriteByte(bmpData.Scan0, offset+1, buffer(0))
         Marshal.WriteByte(bmpData.Scan0, offset+2, buffer(1))
         Marshal.WriteByte(bmpData.Scan0, offset+3, buffer(2))
         offset += 4
      Next
   Next
   bmp.UnlockBits(bmpData)
   surface.Unmap()
   dataStream.Dispose()
   d2TempBitmap.Dispose()
End Sub

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很难看出问题出在哪里，因为没有所有的代码。可能是GDI+位图和ID2D1Bitmap1格式之间的格式不匹配。此外，还必须使用从surface.Map返回的俯仰（也称步幅）值。这是曲面的精确宽度（以字节为单位），可能与图像的宽度不同。看起来

offset

的值是错误的。示例#2 at显示为每行计算的偏移量为

offset=bitmapData.Stride*y

。谢谢@AndrewMorton。这个示例很有帮助，现在我计算每个像素在数据流中的位置，这就完成了。dataStream.Seek（（y*dataRectangle.Pitch）+（x*4），SeekOrigin.Begin）dataStream.Read（缓冲区，0,4）