学步园

1、载入png绘图

     Bitmap bitmap = new Bitmap(frameWidth, frameHeight);
     Graphics g = Graphics.FromImage(bitmap);
     g.DrawImage(Image , new Rectangle(0, 0, bitmap.Width, bitmap.Height), new Rectangle(frameWidth * frame, 0, frameWidth, frameHeight), GraphicsUnit.Pixel);

2、创建内存设备上下文环境

     IntPtr screenDC = Win32.GetDC(IntPtr.Zero);
     IntPtr memDc = Win32.CreateCompatibleDC(screenDC);

3、选择对象到指定的内存设备上下文环境

     hBitmap = bitmap.GetHbitmap(Color.FromArgb(0));
     oldBits = Win32.SelectObject(memDc, hBitmap);

4、定义混合结构

     Win32.BLENDFUNCTION blendFunc = new Win32.BLENDFUNCTION();

      blendFunc.BlendOp = Win32.AC_SRC_OVER;
      blendFunc.SourceConstantAlpha = 255;
      blendFunc.AlphaFormat = Win32.AC_SRC_ALPHA;
      blendFunc.BlendFlags = 0;

5、使用更新分层窗体函数

      Win32.UpdateLayeredWindow(Handle, screenDC, ref topLoc, ref bitMapSize, memDc, ref srcLoc, 0, ref blendFunc, Win32.ULW_ALPHA);

如此，可用具有透明效果的任意形状的png图片做窗体界面。