David Lanham 新 iOS 遊戲 “Hatch” 的官網視頻中，最後小寵物從畫面跑進網頁的效果是如何實現的？

<code class="text">var scale = 1;
var baseHeight = 544 * scale;
var baseWidth = 602 * scale;
var eachFrame = 15;

var canvas = $('<canvas id="canvas"/>').css({
	'position': 'fixed',
	'zIndex': 9999,
	'bottom': '0',
	'overflow': 'hidden',
}).attr({
	'width': baseWidth,
	'height': baseHeight,
});

$('body').append(canvas);


var frameCnt = 0;
var context = canvas[0].getContext('2d');

function animate(isReset) {
	if (isReset) {
		frameCnt = 0;
	};
	// clear
	context.clearRect(0, 0, baseWidth, baseHeight);
	// draw stuff
	context.drawImage(imageObjs[parseInt(frameCnt / eachFrame)], (frameCnt % eachFrame) * baseWidth, 0, baseWidth, baseHeight, 0, 0, baseWidth, baseHeight);
	frameCnt++;
	// request new frame
	if (frameCnt < eachFrame * 2) {
		setTimeout(animate, 1000 / 8);
	} else {
		animate(true);
	}
}

var pic = [
	'http://p1.zhimg.com/8c/fb/8cfbc0eb11019584c7ee0dccd4c8bf66_r.jpg',
	'http://p1.zhimg.com/4f/3d/4f3db206b0fd094ef2fc00ece876ad30_r.jpg'
];


function preLoadImages(imgSrcList, callback) {
	var imageObjs = [];
	var len = imgSrcList.length;
	var callbackAfter = len;

	var preloadInterval = window.setInterval(function() {
		if (callbackAfter === 0) {
			window.clearInterval(preloadInterval);
			callback();
		}
	}, 100);


	for (var i = 0; i < len; i++) {
		imageObjs[i] = new Image();
		imageObjs[i].onload = function() {
			callbackAfter--;
		};
		imageObjs[i].src = imgSrcList[i];
	};



	return imageObjs;
}

var imageObjs = preLoadImages(pic, function() {
	animate(true);
});
</code>