draw something onto the drawing surface (with the clipping region applied) : Clip : Graphics C# Source Code

    
 
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Text;
using System.Windows.Forms;

public class Form1 : Form {

    protected override void OnPaint(PaintEventArgs e) {
    Graphics g = e.Graphics;
    g.FillRectangle(Brushes.White, this.ClientRectangle);
    Rectangle rect = new Rectangle(10, 10, 80, 50);
    g.DrawRectangle(Pens.Black, rect);
    g.SetClip(rect);
    g.FillEllipse(Brushes.Blue, 20, 20, 100, 100);
    }
    public static void Main() {
        Application.Run(new Form1());
    }
}