//DllImport所在的名字空间
using System.Runtime.InteropServices;
[DllImport("User32.dll")]
public extern static System.IntPtr GetDC(System.IntPtr hWnd);
private void button19_Click(object sender, EventArgs e)
{
System.IntPtr DesktopHandle = GetDC(System.IntPtr.Zero);
Graphics g = Graphics.FromHdc(DesktopHandle);
g.DrawRectangle(new Pen(Color.Red),new Rectangle(10,10,100,100));
}

System.Drawing.Image MyImage=new System.Drawing.Bitmap (w,h)；//申请位图对象
System.Drawing.Graphics g=System.Drawing.Graphics.FromImage(MyImage); //申请画图对象
//用白色C清出除
Color C=Color.FromArgb(255,255,255);
g.Clear(C);
 
//画线
g.DrawLine(Pens.Black,x1,y1,x2,y2);
//画一个象素的点
//MyBitmap.SetPixel(x, y, Color.White);

g.DrawImage(MyImage,0,0,h,w); //pictureBox1在(0,0)到(h,w)范围画点
pictureBox1.Image=MyImage;     //这个图片贴到pictureBox1控件上

System.Drawing.Pen myPen = new System.Drawing.Pen(System.Drawing.Color.Red);//画笔
System.Drawing.SolidBrush myBrush = new System.Drawing.SolidBrush(System.Drawing.Color.Red);//画刷
System.Drawing.Graphics formGraphics = this.CreateGraphics();
formGraphics.FillEllipse(myBrush, new Rectangle(0,0,100,200));//画实心椭圆
formGraphics.DrawEllipse(myPen, new Rectangle(0,0,100,200));//空心圆
formGraphics.FillRectangle(myBrush, new Rectangle(0,0,100,200));//画实心方
formGraphics.DrawRectangle(myPen, new Rectangle(0,0,100,200));//空心矩形
formGraphics.DrawLine(myPen, 0, 0, 200, 200);//画线
formGraphics.DrawPie(myPen,90,80,140,40,120,100); //画馅饼图形
//画多边形
formGraphics.DrawPolygon(myPen,new Point[]{ new Point(30,140), new Point(270,250), new Point(110,240), new Point

(200,170), new Point(70,350), new Point(50,200)});  
//清理使用的资源
myPen.Dispose();
myBrush.Dispose();
formGraphics.Dispose();

//在窗体上绘制竖向文本
System.Drawing.Graphics formGraphics = this.CreateGraphics();
string drawString = "Text";
System.Drawing.Font drawFont = new System.Drawing.Font("Arial", 16);
System.Drawing.SolidBrush drawBrush = new System.Drawing.SolidBrush(System.Drawing.Color.Black);
float x = 150.0f;
float y = 50.0f;
System.Drawing.StringFormat drawFormat = new System.Drawing.StringFormat(StringFormatFlags.DirectionVertical);//文本

//垂直
formGraphics.DrawString(drawString, drawFont, drawBrush, x, y);//绘制文本
formGraphics.DrawString(drawString, drawFont, drawBrush, x, y, drawFormat);//绘制垂直文本

//清理使用的资源
drawFont.Dispose();
drawBrush.Dispose();
formGraphics.Dispose();

//该画刷的HatchStyle有DiagonalCross、 ForwardDiagonal、Horizontal、 Vertical、 Solid等不同风格
HatchStyle hs = HatchStyle.Cross; //十字
HatchBrush sb = new HatchBrush(hs,Color.Blue,Color.Red);
g.FillRectangle(sb,50,50,150,150);

Rectangle r = new Rectangle(500, 300, 100, 100);
LinearGradientBrush lb = new LinearGradientBrush(r, Color.Red, Color.Yellow, LinearGradientMode.BackwardDiagonal);
g.FillRectangle(lb, r);
//PathGradientBrush路径渐变，LinearGradientBrush线性渐变

Image bgimage = new Bitmap("E:2065215396.jpg");
brush = new TextureBrush(bgimage); //易一幅图作椭圆的背景
g.FillEllipse(brush,50,50,500,300);