I've created an image service in C# which takes a base layer image (JPG), layers one more more transparent PNG's (32 bit), and then outputs a final JPG image. I'm trying to squeeze every last millisecond out of this function and my code is bottlenecking at the DrawImage call in GDI+. Managed code here:
// 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();
Now, I read about the performance gains obtained by calling GDI directly by P/Invoke and made an attempt at replacing the DrawImage call. I created a unit test to try to duplicate the same functionality of loading a JPG and then layering one transparent PNG on top of it.
Ref: 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);
But this fails to produce a layered image. Just the PNG without the base JPG. What should I be doing differently? I'm a little out of my league when in comes to straight GDI.
I ended up using SharpDX to access both the WIC and Direct2d API's. The results are impressive to say the least. When compositing with Direct2d I'm seeing increased performance as much as 400-500% over GDI+.
I also tried GDI+ and the Task Parallel Library to break up images into four quandrants and do compositing work in each core. The results weren't nearly as signficant as using SharpDX.
Here's the code I ended up using. The reference to "renderSettings" is just a configuration object. Substitute as needed along with the renderLayer image list.