winform GDI基础（一）

1获取画布

（1）从PaintEventArgs类中获取画布

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = e.Graphics;
        }

（2）从Image中获取画布

            Bitmap bm = new Bitmap(this.Width, this.Height);
            Graphics g = Graphics.FromImage(bm);

（3）使用CreateGraphics创建画布

 Graphics g = this.CreateGraphics();

（4）其他方式

从设备上下文的指定句柄创建新的 System.Drawing.Graphics

public static Graphics FromHdc(IntPtr hdc);

从设备上下文的指定句柄和设备的句柄创建新的 System.Drawing.Graphics

public static Graphics FromHdc(IntPtr hdc, IntPtr hdevice);

返回指定设备上下文的 System.Drawing.Graphics

public static Graphics FromHdcInternal(IntPtr hdc);

从窗口的指定句柄创建新的 System.Drawing.Graphics

public static Graphics FromHwnd(IntPtr hwnd);

创建指定 Windows 句柄的新 System.Drawing.Graphics

 public static Graphics FromHwndInternal(IntPtr hwnd);

2绘制图像

            Graphics g = this.CreateGraphics();
            System.Drawing.Pen pen = new System.Drawing.Pen(Color.Red, 2);
            g.DrawLine();//画线
            g.DrawRectangle();//画矩形
            g.DrawEllipse();//画椭圆
            g.DrawArc();//画扇形

3抗锯齿处理

g.SmoothingMode = SmoothingMode.HighQuality;//设置抗锯齿
g.CompositingQuality = CompositingQuality.HighQuality;//提升合成图片质量
g.TextRenderingHint = TextRenderingHint.SingleBitPerPixelGridFit;//去掉文字的锯齿

4处理图像

            Bitmap bm = new Bitmap(200, 200);
            Graphics g = Graphics.FromImage(bm);
            System.Drawing.Pen pen = new System.Drawing.Pen(Color.Red, 4);
            g.DrawLine(pen,new Point(10,10),new Point(100,100));
            bm.Save(Application.StartupPath + @"1.png");
            g.Dispose();
            bm.Dispose();