Create Rectangle

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

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        private bool isMouseDown = false;
        private bool isInsideRect = false;
        private bool lastInside = false;
        Point[] rPoints = new Point[2];
        Rectangle rect;

        public Form1()
        {
            InitializeComponent();
            this.SetStyle(ControlStyles.OptimizedDoubleBuffer, true);
        }

        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            rPoints[0] = rPoints[1] = e.Location;
            isMouseDown = true;
        }

        private void Form1_MouseUp(object sender, MouseEventArgs e)
        {
            rPoints[1] = e.Location;
            isMouseDown = false;
        }

        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            rPoints[1] = e.Location;
            if (isMouseDown)
            {
                rect = getRectanlge(rPoints[0], rPoints[1]);
            }

            isInsideRect = isInRectangle(e.Location, rect);
            DrawRectangles();
            lastInside = isInsideRect;

            UpdateInfo(e.Location, rect);
        }

        private void DrawRectangles()
        {
            Brush brush = !isInsideRect ? new SolidBrush(Color.LightBlue) : new SolidBrush(Color.Blue);

            if ((isInsideRect != lastInside) || isMouseDown)
            {
                Refresh();
                using (Graphics g = this.CreateGraphics())
                    g.FillRectangle(brush, rect);
            }
        }

        private void UpdateInfo(Point mouse, Rectangle rectangle)
        {
            textBox1.Text = string.Format(
                "Rectangle Location: {0}x{1}\r\nRetangle Size: {2}x{3}\r\nMouse Location: {4}x{5}\r\nMouse down: {6}\r\nInside Rectangle: {7}",
                rectangle.X,
                rectangle.Y,
                rectangle.Width,
                rectangle.Height,
                mouse.X,
                mouse.Y,
                isMouseDown,
                isInsideRect);
        }

        public Rectangle getRectanlge(Point StartP, Point EndP)
        {
            return new Rectangle(
                Math.Min(StartP.X, EndP.X),
                Math.Min(StartP.Y, EndP.Y),
                Math.Abs(StartP.X - EndP.X),
                Math.Abs(StartP.Y - EndP.Y)
                );
        }

        private bool isInRectangle(Point mp, Rectangle rect)
        {
            if (mp.X > rect.X && mp.X < (rect.X + rect.Width)
                &&
                mp.Y > rect.Y && mp.Y < (rect.Y + rect.Height))
                return true;
            else
                return false;
        }
    }
}
namespace WindowsFormsApplication2
{
    partial class Form1
    {
        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.textBox1 = new System.Windows.Forms.TextBox();
            this.button1 = new System.Windows.Forms.Button();
            this.SuspendLayout();
            //
            // textBox1
            //
            this.textBox1.Location = new System.Drawing.Point(12, 183);
            this.textBox1.Multiline = true;
            this.textBox1.Name = "textBox1";
            this.textBox1.Size = new System.Drawing.Size(280, 77);
            this.textBox1.TabIndex = 0;
            //
            // button1
            //
            this.button1.Location = new System.Drawing.Point(298, 183);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(75, 23);
            this.button1.TabIndex = 1;
            this.button1.Text = "Reset";
            this.button1.UseVisualStyleBackColor = true;
            //
            // Form1
            //
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(380, 272);
            this.Controls.Add(this.button1);
            this.Controls.Add(this.textBox1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.MouseDown += new System.Windows.Forms.MouseEventHandler(this.Form1_MouseDown);
            this.MouseMove += new System.Windows.Forms.MouseEventHandler(this.Form1_MouseMove);
            this.MouseUp += new System.Windows.Forms.MouseEventHandler(this.Form1_MouseUp);
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private System.Windows.Forms.TextBox textBox1;
        private System.Windows.Forms.Button button1;
    }
}
namespace WindowsFormsApplication2
{
    static class Program
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}