Graphics g;
g=this.CreateGraphics()//画布为当前窗体
g=textbox1.CreateGraphics()//画布为textbox

• SolidBrush 纯色填充
  SolidBrush(Color) Initializes a new SolidBrush object of the specified color.
• TextureBrush 图片填充
  TextureBrush(Image) Initializes a new TextureBrush object that uses the specified image.
  TextureBrush(Image, Rectangle) Initializes a new TextureBrush object that uses the specified image and bounding rectangle.
  .......
• LinearGradientBrush 渐变填充
  LinearGradientBrush(Point, Point, Color, Color) Initializes a new instance of the LinearGradientBrush class with the specified points and colors.