C#中创建Alpha混色效果

在Visual Studio中创建Windows窗体程序，将Form调整到一定大小，并将背景色改为白色。

然后，右击Form，选择【查看代码】，在头部添加下面的命名空间：

using System.Drawing.Drawing2D;

在窗体的构造函数后添加如下代码：（构造函数即public Form1(){InitializeComponent();}后面）

protected override void OnPaint(PaintEventArgs e)
        {
            Graphics g = e.Graphics;
            //创建一个填充矩形
            SolidBrush brush = new SolidBrush(Color.BlueViolet);
            g.FillRectangle(brush, 180, 70, 200, 150);

    //创建一个位图，其中的两个矩形之间有透明效果
            Bitmap bm1 = new Bitmap(200, 100);
            Graphics bg1 = Graphics.FromImage(bm1);
            SolidBrush redBrush = new SolidBrush(Color.FromArgb(210, 255, 0, 0));
            SolidBrush greenBrush = new SolidBrush(Color.FromArgb(210, 0, 255, 0));
            bg1.FillRectangle(redBrush, 0, 0, 150, 70);
            bg1.FillRectangle(greenBrush, 30, 30, 150, 70);
            g.DrawImage(bm1, 100, 50);

    //创建第二个位图，其中两个矩形之间没有透明效果
            Bitmap bm2 = new Bitmap(200, 100);
            Graphics bg2 = Graphics.FromImage(bm2);
            bg2.CompositingMode = CompositingMode.SourceCopy;
            bg2.FillRectangle(redBrush, 0, 0, 150, 70);
            bg2.FillRectangle(greenBrush, 30, 30, 150, 70);
            g.CompositingQuality = CompositingQuality.GammaCorrected;

   //g.CompositingMode = CompositingMode.SourceCopy;

    g.DrawImage(bm2, 300, 100);
            Bitmap bm3 = new Bitmap(200, 100);
            Graphics bg3 = Graphics.FromImage(bm3);
            redBrush = new SolidBrush(Color.FromArgb(100, 255, 0, 0));
            greenBrush = new SolidBrush(Color.FromArgb(100, 0, 255, 0));
            bg3.FillRectangle(redBrush, 0, 0, 150, 70);
            bg3.FillRectangle(greenBrush, 30, 30, 150, 70);
            g.DrawImage(bm3, 100, 150);
        }

演示效果如下：