C#--GDI+的Alpha设置

下面的例子演示了如何使用Color结构的Alpha成分，首先从Color结构中创建两个Color实例，一个是c1,它是蓝色的，其alpha值为100,另一个是绿色的alpha值为50.接着绘制三个实心图形

public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = e.Graphics;
            g.FillRectangle(Brushes.White, this.ClientRectangle);
            Color c1 = Color.FromArgb(100, Color.Blue);
            Color c2 = Color.FromArgb(50, Color.Blue);

            g.FillEllipse(Brushes.Red, 20, 20, 80, 80);
            Point[] pa = new Point[] {
                new Point(150,40),
                new Point(90,40),
                new Point(90,120)
            };
            g.FillPolygon(new SolidBrush(c2), pa);

        }
    }