Form1.cs

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

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        int x;
        int y;
        int rec_width;
        int rec_height;
        Form1 form_ref = null;
        int scale = 1;
        Boolean growing= false;


        public Form1()
        {
            InitializeComponent();
            form_ref = this;
            rec_height = this.Height;
            rec_width = this.Width;
        }



        private void Form1_Paint(object sender, PaintEventArgs e)
        {

            Console.WriteLine("scale ={4} x={0}, y={1}, w={2}, h={3}", x, y, rec_width, rec_height, scale);
            Rectangle rect = new Rectangle(x, y, rec_width, rec_height);
            e.Graphics.DrawRectangle(Pens.Red, rect);
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            x +=scale;
            y +=scale;
            rec_width = form_ref.Width-(x*2);
            rec_height = form_ref.Height-(y*2);

            if (growing)
                scale--;
            else 
                scale++;


            if (rec_width < 0 || rec_height < 0)
            {
                growing = true;
                //reset();
            }
            else if(rec_width > form_ref.Width || rec_height > form_ref.Height)
                growing = false;

            Invalidate();

        }

        private void reset()
        {
            
                rec_width = form_ref.Width;
                rec_height = form_ref.Height;
                x = 0; y = 0;
                scale = 1;
         
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            timer1.Start();
        }
    }
}