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HTML

              
                <canvas id="myCanvas" width="500" height="300" style="border: solid 2px lightgrey;"></canvas>
              
            
!

CSS

              
                
              
            
!

JS

              
                /**
 * Created on 2015-04-20.
 */
var canvas;
var context;
var x = 200; //start position
var y = 100; //start position
var mx = 2; //x coordinate translation
var my = 4; //y coordinate translation
var WIDTH = 500; //canvas boundaries
var HEIGHT = 300; //canvas boundaries

window.onload = init(); //start the ball

function init() {
	canvas = document.getElementById("myCanvas"); //assign the canvas to a variable
	context = canvas.getContext("2d"); //Create context method to enable draw methods
	// return setInterval(draw, 20); //call the draw function every 20 milliseconds
	draw();
}

function circle(x, y, r) {
	context.beginPath(); //starts the drawing path
	context.arc(x, y, r, 0, Math.PI * 2, true); //define the size and shape of circle
	context.fill(); //fill the circle to display it
}

function draw() {
	clear();

	//parameters are the x and y coordinates and the radius(size)
	circle(x, y, 20);

	/*
	 * Up to here should draw a circle in the bottom right corner
	 * The circle gets redrawn every 20 milliseconds
	 * But there is no change in position
	 */

	//Check to see if the ball is a side of the canvas
	if (x + mx > WIDTH || x + mx < 0) {
		mx = -mx; //change the x direction
	}
	//check to see if the ball is at the top or bottom of the canvas
	if (y + my > HEIGHT || y + my < 0) {
		my = -my; //change the y direction
	}

	x += mx; //change the next x coordinate of the ball
	y += my; //change the next y coordinate of the ball

	/*
	 * Now the ball moves and bounces around in the canvas
	 * However it leaves behind a trail
	 * We need to clear the canvas before each move
	 */

	window.requestAnimationFrame(draw);
}

function clear() {
	//remove any drawings from the canvas
	context.clearRect(0, 0, WIDTH, HEIGHT);
}

              
            
!
999px

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