我在C#中创建了一个图像服务,它接受一个基础层图片(JPG),将一个或多个透明的PNG(32位)覆盖在其上,并输出最终的JPG图像。 我试图从这个函数中挤出每一毫秒,并且我的代码在GDI+的DrawImage调用处成为瓶颈。 下面是我的托管代码:
// Load base image and create graphics
Image image = LoadImage(renderSettings.RenderedImageDirectory + baseLayer);
Graphics graphics = Graphics.FromImage(image);
graphics.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
graphics.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
graphics.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighSpeed;
// Draw additional layers to final image
for (int i = 1; i < renderLayers.Count; i++) {
// SLOW -- LoadImage just a utility method that returns an Image from disk or cache
graphics.DrawImage(LoadImage(renderSettings.RenderedImageDirectory + renderLayers[i]), 0, 0, image.Width, image.Height);
}
if (graphics != null) graphics.Dispose();
现在,我了解到通过P/Invoke直接调用GDI可以获得性能提升,并尝试替换DrawImage调用。我创建了一个单元测试来尝试复制加载JPG并在其上叠加一个透明PNG的相同功能。
参考:http://social.msdn.microsoft.com/Forums/en-US/winforms/thread/29582142-0068-40dd-bd99-4b3883a76350
Bitmap sourceImage = new Bitmap("c:\\base.jpg");
Bitmap overlayImage = new Bitmap("c:\\layer1.png");
// NOTE: ImageHelper is a utility class containing all the P/Invoke stuff
// Get source image in memory
Graphics sourceImageGraphics = Graphics.FromImage(sourceImage);
IntPtr sourceImageHDC = sourceImageGraphics.GetHdc();
IntPtr sourceImageCDC = ImageHelper.CreateCompatibleDC(sourceImageHDC);
IntPtr sourceImageHandle = sourceImage.GetHbitmap();
ImageHelper.SelectObject(sourceImageCDC, sourceImageHandle);
// Get overlay image in memory
Graphics overlayImageGraphics = Graphics.FromImage(overlayImage);
IntPtr overlayImageHDC = overlayImageGraphics.GetHdc();
IntPtr overlayImageCDC = ImageHelper.CreateCompatibleDC(overlayImageHDC);
IntPtr overlayImageHandle = overlayImage.GetHbitmap();
ImageHelper.SelectObject(overlayImageCDC, overlayImageHandle);
ImageHelper.BitBlt(sourceImageHDC, 0, 0, sourceImage.Width, sourceImage.Height, overlayImageCDC, 0, 0, ImageHelper.TernaryRasterOperations.SRCAND);
ImageHelper.AlphaBlend(sourceImageHDC, 0, 0, sourceImage.Width, sourceImage.Height, overlayImageCDC, 0, 0, sourceImage.Width, sourceImage.Height, new ImageHelper.BLENDFUNCTION(ImageHelper.AC_SRC_OVER, 0, 0xff, ImageHelper.AC_SRC_ALPHA));
// Release source Image memory.
ImageHelper.DeleteDC(sourceImageCDC);
ImageHelper.DeleteObject(sourceImageHandle);
sourceImageGraphics.ReleaseHdc(sourceImageHDC);
sourceImageGraphics.Dispose();
// Release overlay Image memory.
ImageHelper.DeleteDC(overlayImageCDC);
ImageHelper.DeleteObject(overlayImageHandle);
overlayImageGraphics.ReleaseHdc(overlayImageHDC);
overlayImageGraphics.Dispose();
// Save to jpg
sourceImage.Save("c:\\output.jpg", ImageFormat.Jpeg);
但是这样无法产生分层图像,只有没有基础JPG的PNG。我应该做些什么不同的事情呢?当涉及到纯GDI时,我有点力不从心。