HTML 5 Canvas Project:
Project Description
please watch this video carefully to understand how code works.
Code:
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>Canvas Test Using Double Buffering</title>
<script type="text/javascript">
var canvas = null;
var context = null;
var bufferCanvas = null;
var bufferCanvasCtx = null;
var flakeArray = [];
var flakeTimer = null;
var maxFlakes = 200;
function Flake() {
this.x = Math.round(Math.random() * context.canvas.width);
this.y = -10;
this.drift = Math.random();
this.speed = Math.round(Math.random() * 5) + 1;
this.width = (Math.random() * 3) + 2;
this.height = this.width;
}
function init() {
canvas = document.getElementById('testCanvas');
context = canvas.getContext("2d");
bufferCanvas = document.createElement("canvas");
bufferCanvasCtx = bufferCanvas.getContext("2d");
bufferCanvasCtx.canvas.width = context.canvas.width;
bufferCanvasCtx.canvas.height = context.canvas.height;
// initialize the rects
flakeTimer = setInterval(addFlake, 200);
Draw();
setInterval(animate, 30);
}
function addFlake() {
flakeArray[flakeArray.length] = new Flake();
if (flakeArray.length == maxFlakes)
clearInterval(flakeTimer);
}
function blank() {
bufferCanvasCtx.fillStyle = "#000";
bufferCanvasCtx.fillRect(0,0,bufferCanvasCtx.canvas.width, bufferCanvasCtx.canvas.height);
}
function animate() {
Update();
Draw();
}
function Update() {
for (var i = 0; i < flakeArray.length; i++) {
if (flakeArray[i].y < context.canvas.height) {
flakeArray[i].y += flakeArray[i].speed;
if (flakeArray[i].y > context.canvas.height)
flakeArray[i].y = -5;
flakeArray[i].x += flakeArray[i].drift;
if (flakeArray[i].x > context.canvas.width)
flakeArray[i].x = 0;
}
}
}
function Draw(){
context.save();
/*
// create a clipping region
bufferCanvasCtx.beginPath();
bufferCanvasCtx.fillStyle="black";
bufferCanvasCtx.fillRect(0,0,bufferCanvas.width,bufferCanvas.height);
bufferCanvasCtx.arc(bufferCanvas.width/2,bufferCanvas.height/2,bufferCanvas.height/3,0,2*Math.PI);
bufferCanvasCtx.clip();
*/
blank();
for (var i = 0; i < flakeArray.length; i++) {
bufferCanvasCtx.fillStyle = "white";
bufferCanvasCtx.fillRect(flakeArray[i].x,flakeArray[i].y,flakeArray[i].width,flakeArray[i].height);
}
// copy the entire rendered image from the buffer canvas to the visible one
context.drawImage(bufferCanvas, 0,0,bufferCanvas.width, bufferCanvas.height);
context.restore();
//This is extra added
}
</script>
</head>
<body onload="init()">
<canvas id="testCanvas" width="800" height="800">
Canvas not supported
</canvas>
</body>
</html>
