HTML5 Bouncing rectangle example.html

<!DOCTYPE=html>
<html><body>
<canvas id="myCanvas" width="320" height="240" style="border:1px solid #d3d3d3;">
Use different browser.
</canvas>
<script>
    var c=document.getElementById("myCanvas");
    var ctx=c.getContext("2d");
    var rx = c.width/2;
    var ry = c.height/2;
    var rw = 16;
    var rh = 16;
    var rm = 5;
    gameloop=setInterval(doGameLoop,16);
    function doGameLoop(){
        ctx.clearRect(0,0,c.width,c.height);
        ctx.fillRect(rx,ry,rw,rh);
        
        // Update the y position
        ry -= rm;
        
        // Decrease the modifier by a value.
        rm -=.1
        
        // If the rect is back to the original position 
        // then set the modifier to 5 again and set
        // the y position back to its start position.
        if(rm < -5){
            rm = 5;
            ry = c.height/2;
        }
        
    }
</script></body></html>