在Windows Mobile 显示透明 PNG的方法

同样在移植的过程中，发现 .Net compact Framework 不支持透明图像。原本具有透明属性的Png (含有 alpha通道），通过 Graphics.DrawImage 显示之后，不再具有透明特性。这对于地图分层显示带了麻烦。举例来说。带地名卫星地图一般是由两层图片叠加而成。

两个图片叠加形成最后的图片

当由于.Net Compact Framework缺省不支持透明图像，两幅图叠加是 道路图回彻底覆盖掉下面的卫星图。原来的透明色变成白色。 同样如果再有其它图层（比如路径），又覆盖掉道路图。
经过Google 搜索，有两种方法可以实现在Windows mobile 上透明图像的显示。

是通过IImagingFactory 接口

using System; using System.Drawing; using System.Runtime.InteropServices; namespace DotNetPocketStreet.Drawing { enum ImageLockMode { ImageLockModeRead = 0x0001, ImageLockModeWrite = 0x0002, ImageLockModeUserInputBuf = 0x0004 }; // Pulled from gdipluspixelformats.h in the Windows Mobile 5.0 Pocket PC SDK public enum PixelFormatID : int { PixelFormatIndexed = 0x00010000, // Indexes into a palette PixelFormatGDI = 0x00020000, // Is a GDI-supported format PixelFormatAlpha = 0x00040000, // Has an alpha component PixelFormatPAlpha = 0x00080000, // Pre-multiplied alpha PixelFormatExtended = 0x00100000, // Extended color 16 bits/channel PixelFormatCanonical = 0x00200000, PixelFormatUndefined = 0, PixelFormatDontCare = 0, PixelFormat1bppIndexed = (1 | ( 1 << <img class="wp-smiley" alt="8)" src="http://www.imobilebbs.com/wordpress/wp-includes/images/smilies/icon_cool.gif"> | PixelFormatIndexed | PixelFormatGDI), PixelFormat4bppIndexed = (2 | ( 4 << <img class="wp-smiley" alt="8)" src="http://www.imobilebbs.com/wordpress/wp-includes/images/smilies/icon_cool.gif"> | PixelFormatIndexed | PixelFormatGDI), PixelFormat8bppIndexed = (3 | ( 8 << <img class="wp-smiley" alt="8)" src="http://www.imobilebbs.com/wordpress/wp-includes/images/smilies/icon_cool.gif"> | PixelFormatIndexed | PixelFormatGDI), PixelFormat16bppRGB555 = (5 | (16 << <img class="wp-smiley" alt="8)" src="http://www.imobilebbs.com/wordpress/wp-includes/images/smilies/icon_cool.gif"> | PixelFormatGDI), PixelFormat16bppRGB565 = (6 | (16 << <img class="wp-smiley" alt="8)" src="http://www.imobilebbs.com/wordpress/wp-includes/images/smilies/icon_cool.gif"> | PixelFormatGDI), PixelFormat16bppARGB1555 = (7 | (16 << <img class="wp-smiley" alt="8)" src="http://www.imobilebbs.com/wordpress/wp-includes/images/smilies/icon_cool.gif"> | PixelFormatAlpha | PixelFormatGDI), PixelFormat24bppRGB = (8 | (24 << <img class="wp-smiley" alt="8)" src="http://www.imobilebbs.com/wordpress/wp-includes/images/smilies/icon_cool.gif"> | PixelFormatGDI), PixelFormat32bppRGB = (9 | (32 << <img class="wp-smiley" alt="8)" src="http://www.imobilebbs.com/wordpress/wp-includes/images/smilies/icon_cool.gif"> | PixelFormatGDI), PixelFormat32bppARGB = (10 | (32 << <img class="wp-smiley" alt="8)" src="http://www.imobilebbs.com/wordpress/wp-includes/images/smilies/icon_cool.gif"> | PixelFormatAlpha | PixelFormatGDI | PixelFormatCanonical), PixelFormat32bppPARGB = (11 | (32 << <img class="wp-smiley" alt="8)" src="http://www.imobilebbs.com/wordpress/wp-includes/images/smilies/icon_cool.gif"> | PixelFormatAlpha | PixelFormatPAlpha | PixelFormatGDI), PixelFormat48bppRGB = (12 | (48 << <img class="wp-smiley" alt="8)" src="http://www.imobilebbs.com/wordpress/wp-includes/images/smilies/icon_cool.gif"> | PixelFormatExtended), PixelFormat64bppARGB = (13 | (64 << <img class="wp-smiley" alt="8)" src="http://www.imobilebbs.com/wordpress/wp-includes/images/smilies/icon_cool.gif"> | PixelFormatAlpha | PixelFormatCanonical | PixelFormatExtended), PixelFormat64bppPARGB = (14 | (64 << <img class="wp-smiley" alt="8)" src="http://www.imobilebbs.com/wordpress/wp-includes/images/smilies/icon_cool.gif"> | PixelFormatAlpha | PixelFormatPAlpha | PixelFormatExtended), PixelFormatMax = 15 } // Pulled from imaging.h in the Windows Mobile 5.0 Pocket PC SDK public enum BufferDisposalFlag : int { BufferDisposalFlagNone, BufferDisposalFlagGlobalFree, BufferDisposalFlagCoTaskMemFree, BufferDisposalFlagUnmapView } // Pulled from imaging.h in the Windows Mobile 5.0 Pocket PC SDK public enum InterpolationHint : int { InterpolationHintDefault, InterpolationHintNearestNeighbor, InterpolationHintBilinear, InterpolationHintAveraging, InterpolationHintBicubic } // Pulled from gdiplusimaging.h in the Windows Mobile 5.0 Pocket PC SDK public struct BitmapData { public uint Width; public uint Height; public int Stride; public PixelFormatID PixelFormat; public IntPtr Scan0; public IntPtr Reserved; } // Pulled from imaging.h in the Windows Mobile 5.0 Pocket PC SDK public struct ImageInfo { public uint GuidPart1; // I am being lazy here, I don't care at this point about the RawDataFormat GUID public uint GuidPart2; // I am being lazy here, I don't care at this point about the RawDataFormat GUID public uint GuidPart3; // I am being lazy here, I don't care at this point about the RawDataFormat GUID public uint GuidPart4; // I am being lazy here, I don't care at this point about the RawDataFormat GUID public PixelFormatID pixelFormat; public uint Width; public uint Height; public uint TileWidth; public uint TileHeight; public double Xdpi; public double Ydpi; public uint Flags; } // Pulled from imaging.h in the Windows Mobile 5.0 Pocket PC SDK [ComImport, Guid("327ABDA7-072B-11D3-9D7B-0000F81EF32E"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)] [ComVisible(true)] public interface IImagingFactory { uint CreateImageFromStream(); // This is a place holder, note the lack of arguments uint CreateImageFromFile(string filename, out INativeImage image); // We need the MarshalAs attribute here to keep COM interop from sending the buffer down as a Safe Array. uint CreateImageFromBuffer([MarshalAs(UnmanagedType.LPArray)] byte[] buffer, uint size, BufferDisposalFlag disposalFlag, out INativeImage image); uint CreateNewBitmap(uint width, uint height, PixelFormatID pixelFormat, out IBitmapImage bitmap); uint CreateBitmapFromImage(INativeImage image, uint width, uint height, PixelFormatID pixelFormat, InterpolationHint hints, out IBitmapImage bitmap); uint CreateBitmapFromBuffer(); // This is a place holder, note the lack of arguments uint CreateImageDecoder(); // This is a place holder, note the lack of arguments uint CreateImageEncoderToStream(); // This is a place holder, note the lack of arguments uint CreateImageEncoderToFile(); // This is a place holder, note the lack of arguments uint GetInstalledDecoders(); // This is a place holder, note the lack of arguments uint GetInstalledEncoders(); // This is a place holder, note the lack of arguments uint InstallImageCodec(); // This is a place holder, note the lack of arguments uint UninstallImageCodec(); // This is a place holder, note the lack of arguments } // Pulled from imaging.h in the Windows Mobile 5.0 Pocket PC SDK [ComImport, Guid("327ABDA9-072B-11D3-9D7B-0000F81EF32E"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)] [ComVisible(true)] public interface INativeImage { uint GetPhysicalDimension(out Size size); uint GetImageInfo(out ImageInfo info); uint SetImageFlags(uint flags); uint Draw(IntPtr hdc, ref Rectangle dstRect, IntPtr NULL); // "Correct" declaration: uint Draw(IntPtr hdc, ref Rectangle dstRect, ref Rectangle srcRect); uint PushIntoSink(); // This is a place holder, note the lack of arguments uint GetThumbnail(uint thumbWidth, uint thumbHeight, out INativeImage thumbImage); } // Pulled from imaging.h in the Windows Mobile 5.0 Pocket PC SDK [ComImport, Guid("327ABDAA-072B-11D3-9D7B-0000F81EF32E"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)] [ComVisible(true)] public interface IBitmapImage { uint GetSize(out Size size); uint GetPixelFormatID(out PixelFormatID pixelFormat); uint LockBits(ref Rectangle rect, uint flags, PixelFormatID pixelFormat, out BitmapData lockedBitmapData); uint UnlockBits(ref BitmapData lockedBitmapData); uint GetPalette(); // This is a place holder, note the lack of arguments uint SetPalette(); // This is a place holder, note the lack of arguments } }

调用方法如下

using (Graphics gxBuffer = Graphics.FromImage(backBuffer)) { // Since we nop'd OnPaintBackground, take care of it here gxBuffer.Clear(this.BackColor); // Ask the Image object from Imaging to draw itself. IntPtr hdcDest = gxBuffer.GetHdc(); Rectangle dstRect = new Rectangle(100, 100, 148, 148); imagingResource.Draw(hdcDest, ref dstRect, IntPtr.Zero); gxBuffer.ReleaseHdc(hdcDest); // Ask the Image object from Imaging to draw itself. /*IntPtr*/ hdcDest = gxBuffer.GetHdc(); // This is redundant, but keeps the necessary code together /*Rectangle*/ dstRect = new Rectangle(50, 70, 50+132, 70+132); imagingImage.Draw(hdcDest, ref dstRect, IntPtr.Zero); gxBuffer.ReleaseHdc(hdcDest); } // Put the final composed image on screen. e.Graphics.DrawImage(backBuffer, 0, 0);

文档可参考 http://msdn.microsoft.com/en-us/library/aa452202.aspx

另外一种方法还是采用Manged code, 对于预先知道透明色值的图像，比如地图API中的路径，背景色总为0xFFE0E0E0
可以使用下面方法

ImageAttributes _imageAttributes = new ImageAttributes(); Color color = Color.FromArgb(0xE0E0E0); _imageAttributes.SetColorKey(color, color); Rectangle dstRect = new Rectangle(x, y, netImage.GetWidth(), netImage.GetHeight()); gxBuffer.DrawImage(netImage._bitmap, dstRect, 0, 0, netImage.GetWidth(), netImage.GetHeight(), GraphicsUnit.Pixel, _imageAttributes);

最终结果如下图