2D Graphics C#

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Windows.Forms;
   
class TriangleGradientBrush: Form
{
     public static void Main()
     {
          Application.Run(new TriangleGradientBrush());
     }
     public TriangleGradientBrush()
     {
          ResizeRedraw = true;
     }
     protected override void OnPaint(PaintEventArgs pea)
     {
          DoPage(pea.Graphics, ForeColor,ClientSize.Width, ClientSize.Height);
     }       
     protected void DoPage(Graphics grfx, Color clr, int cx, int cy)
     {
          Point[] apt  = { new Point(cx,  0),
                           new Point(cx, cy),
                           new Point(0,  cy) };
   
          PathGradientBrush pgbrush = new PathGradientBrush(apt);
   
          grfx.FillRectangle(pgbrush, 0, 0, cx, cy);
     }
}