平面png與位圖頂部的c＃

Question

我想在純色位圖上用透明度平鋪一個png。

到目前爲止我有此

using (System.Drawing.Image backImage = System.Drawing.Image.FromFile(layer1imagename)) 

    using (System.Drawing.Image frontImage = System.Drawing.Image.FromFile(HttpContext.Current.Server.MapPath("~/") + layer2)) 

    using (Image IMG1 = new Bitmap(251, 400)) 
    using (Graphics compositeGraphics = Graphics.FromImage(IMG1)) 
    { 
     compositeGraphics.CompositingMode = System.Drawing.Drawing2D.CompositingMode.SourceCopy; 
     compositeGraphics.DrawImageUnscaled(backImage, 0, 0); 
     compositeGraphics.DrawImageUnscaled(frontImage, 0, 0); 
     compositeGraphics.Dispose(); 
     frontImage.Dispose(); 
     backImage.Dispose(); 
     IMG1.Save(layer1imagename, System.Drawing.Imaging.ImageFormat.Png); 
    } 

然而這原來除去頂層的透明度。我如何保留頂部的透明PNG？

Answer 1

變更using (Image IMG1 = new Bitmap(251, 400))變爲using (Image IMG1 = new Bitmap(251, 400, PixelFormat.Format32bppArgb))。

爲MSDN的引用，請參閱：

• http://msdn.microsoft.com/en-us/library/3z132tat.aspx
• http://msdn.microsoft.com/en-us/library/system.drawing.imaging.pixelformat.aspx

編輯 - 按評論：

要畫你想你需要使用一個不同的CompositingMode - SourceOver instead of SourceCopy的PNG。