System.Drawing.Drawing2D.LinearGradientBrush

https://msdn.microsoft.com/en-us/library/system.drawing.drawing2d.lineargradientbrush(v=vs.110).aspx

横向渐变

LinearGradientBrush linGrBrush = new LinearGradientBrush(
      new Point(0, 10),
      new Point(200, 10),
      Color.FromArgb(255, 255, 0, 0),   // Opaque red
      Color.FromArgb(255, 0, 0, 255));  // Opaque blue

            Pen pen = new Pen(linGrBrush);

            //public void DrawLine(Pen pen, int x1, int y1, int x2, int y2);
            e.Graphics.DrawLine(pen, 0, 10, 200, 10);

            //public void FillEllipse(Brush brush, int x, int y, int width, int height);
            //x,y是矩形的左上角的点的坐标，然后是宽和高。在矩形内部画椭圆
            e.Graphics.FillEllipse(linGrBrush, 0, 30, 200, 100);

            //public void FillRectangle(Brush brush, int x, int y, int width, int height);
            e.Graphics.FillRectangle(linGrBrush, 0, 155, 500, 30);

 new Point(0, 10), new Point(200, 10),

new Point(0, 10),  new Point(100, 10),

纵向渐变

  LinearGradientBrush linGrBrush = new LinearGradientBrush(
      new Point(0, 0),
      new Point(0, 30),
      Color.FromArgb(255, 255, 0, 0),   // Opaque red
      Color.FromArgb(255, 0, 0, 255));  // Opaque blue

            Pen pen = new Pen(linGrBrush);

            //public void DrawLine(Pen pen, int x1, int y1, int x2, int y2);
            e.Graphics.DrawLine(pen, 100, 0, 100, 30);

            //public void FillEllipse(Brush brush, int x, int y, int width, int height);
            //x,y是矩形的左上角的点的坐标，然后是宽和高。在矩形内部画椭圆
            e.Graphics.FillEllipse(linGrBrush, 0, 60, 200, 120);

            //public void FillRectangle(Brush brush, int x, int y, int width, int height);
            e.Graphics.FillRectangle(linGrBrush, 0, 210, 500, 30);

需要注意的是，纵向的渐变，是从坐标0开始的，而不是图形的0开始

假如最后一个矩形，左上角坐标改为(0,190)，那么渐变的起始颜色，是从三分之一处开始的

如下图