C#——GDI简单绘图

 public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = this.CreateGraphics();      //绘图用到的类
            Pen pen = new Pen(Brushes.Red);     //画笔
            Point p1 = new Point(30, 50);   //坐标点
            Point p2 = new Point(250, 250);   //坐标点
            g.DrawLine(pen, p1, p2);    //两点连成线
        }

        private void button1_Click(object sender, EventArgs e)
        {
            Graphics g = this.CreateGraphics();
            Pen pen = new Pen(Brushes.Red);
            Size size = new Size(100, 100);  //大小
            Rectangle rec = new Rectangle(new Point(50, 50), size);  //一个起始点，大小表示长和宽
            g.DrawRectangle(pen, rec);    //画矩形
           // SolidBrush brush = new SolidBrush(Color.Blue);
            //g.FillRectangle(brush, rec);
            LinearGradientBrush lbush = new LinearGradientBrush(rec,Color.Red,Color.Yellow,LinearGradientMode.BackwardDiagonal);   //渐变色
            g.FillRectangle(lbush,rec);   //填充渐变色到矩形里
        }

        private void button2_Click(object sender, EventArgs e)
        {
            Graphics g = this.CreateGraphics();
            Pen pen = new Pen(Brushes.Black);
            Size size = new Size(180, 180);
            Rectangle rec = new Rectangle(new Point(200, 200), size);
            g.DrawPie(pen, rec, 90, 90);  //后面两个参数表示角度，起始角和终角，这个画出来是一个四分之一的圆
            LinearGradientBrush lbush = new LinearGradientBrush(rec, Color.Red, Color.Yellow, LinearGradientMode.BackwardDiagonal);
            g.FillPie(lbush,rec,90,90);
        }

        private void button3_Click(object sender, EventArgs e)
        {
            Size size = new Size(180, 180);
            Rectangle rec = new Rectangle(new Point(400, 400), size);
            Graphics g = this.CreateGraphics();
            Pen pen = new Pen(Color.Blue,100);
            g.DrawEllipse(pen,rec);
            LinearGradientBrush lbush = new LinearGradientBrush(rec, Color.White, Color.Blue, LinearGradientMode.BackwardDiagonal);
            g.FillEllipse(lbush, rec);
        }
    }