?using System;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Reflection;

namespace AlphaBlendTest
{

   public class DrawTransp
    {

        private struct BlendFunction
        {
            public byte BlendOp;//源混合操作
            public byte BlendFlags;//必須是0
            public byte SourceConstantAlpha;//0到255間的值，這里0表示完全透明，255表示完全不透明。
            public byte AlphaFormat;//有兩個值 0表示常量alpha值，AC_SRC_ALPHA表示每個像素有各自的alpha通道

        }

        private enum BlendOperation : byte
        {
            AC_SRC_OVER = 0x00//表示根據源alpha值把源圖像疊加到目標圖像上
        }

        private enum BlendFlags : byte
        {
            Zero = 0x00
        }

        private enum SourceConstantAlpha : byte
        {
            Transparent = 0x00,
            Opaque = 0xFF
        }

        private enum AlphaFormat : byte
        {
            AC_SRC_ALPHA = 0x01
        }

        private class PlatformAPIs
        {   
            /// <summary>
            /// 用于繪制透明或半透明的位圖，WinCE5.0+的版本支持，
            /// </summary>
            /// <param name="hdcDest">目標設備圖面的句柄</param>
            /// <param name="xDest">繪制目標圖面的x軸坐標</param>
            /// <param name="yDest">繪制目標圖面的y軸坐標</param>
            /// <param name="cxDest">目標矩形的寬</param>
            /// <param name="cyDest">目標矩形的高</param>
            /// <param name="hdcSrc">源設備圖面的句柄</param>
            /// <param name="xSrc">源x坐標</param>
            /// <param name="ySrc">源y坐標</param>
            /// <param name="cxSrc">源圖寬</param>
            /// <param name="cySrc">源圖高</param>
            /// <param name="blendFunction">BLENDFUNCTION結構，控制源和目標位圖的混合方式</param>
            /// <returns></returns>
            [DllImport("coredll.dll")]           
            extern public static Int32 AlphaBlend(IntPtr hdcDest, Int32 xDest, Int32 yDest, Int32 cxDest, Int32 cyDest, IntPtr hdcSrc, Int32 xSrc, Int32 ySrc, Int32 cxSrc, Int32 cySrc, BlendFunction blendFunction);

        }

       public DrawTransp()
        {

          
           
        }

       
     public static void DrawTime(string time, Graphics gx,int x, int y)
     {
       Font timeFont  = new Font("Tahoma", 32, FontStyle.Regular);
         SizeF size = gx.MeasureString(time, timeFont);
         //int x = this.Width / 2 - (int)size.Width / 2;
         gx.DrawString(time, timeFont, new SolidBrush(Color.WhiteSmoke), x, y);

     }

       /// <summary>
       /// 繪制透明圖像
       /// </summary>
       /// <param name="gx">繪圖圖面</param>
       /// <param name="image">需要繪制的位圖</param>
       /// <param name="transp">透明度trasp/250</param>
       /// <param name="x">繪圖起點的橫坐標</param>
       /// <param name="y">繪圖起點的縱坐標</param>
        public static void DrawAlpha(Graphics gx, Bitmap image, byte transp, int x, int y)
        {
            using (Graphics gxSrc = Graphics.FromImage(image))
            {
                IntPtr hdcDst = gx.GetHdc();
                IntPtr hdcSrc = gxSrc.GetHdc();
                BlendFunction blendFunction = new BlendFunction();
                blendFunction.BlendOp = (byte)BlendOperation.AC_SRC_OVER;  
                blendFunction.BlendFlags = (byte)BlendFlags.Zero;        
                blendFunction.SourceConstantAlpha = transp;
                blendFunction.AlphaFormat = (byte)0;   
                PlatformAPIs.AlphaBlend(hdcDst, x, y, image.Width, image.Height, hdcSrc, 0, 0, image.Width, image.Height, blendFunction);
                gx.ReleaseHdc(hdcDst);    
                gxSrc.ReleaseHdc(hdcSrc);       
            }
        }





    }
}