HTML5圓形波浪載入動畫特效

HTML5圓形波浪載入動畫特效是一款原生html5+css3+canvas波浪滾動上升載入動畫，圓形載入容器效果。

var wave = (function () {

var ctx;
var waveImage;
var canvasWidth;
var canvasHeight;
var needAnimate = false;

function init (callback) {
var wave = document.getElementById('wave');
var canvas = document.createElement('canvas');
if (!canvas.getContext) return;
ctx = canvas.getContext('2d');
canvasWidth = wave.offsetWidth;
canvasHeight = wave.offsetHeight;
canvas.setAttribute('width', canvasWidth);
canvas.setAttribute('height', canvasHeight);
wave.appendChild(canvas);
waveImage = new Image();
waveImage.onload = function () {
waveImage.onload = null;
callback();
}
waveImage.src = 'images/wave.png';
}

function animate () {
var waveX = 0;
var waveY = 0;
var waveX_min = -203;
var waveY_max = canvasHeight * 0.7;
var requestAnimationFrame = 
window.requestAnimationFrame || 
window.mozRequestAnimationFrame || 
window.webkitRequestAnimationFrame || 
window.msRequestAnimationFrame ||
function (callback) { window.setTimeout(callback, 1000 / 60); };
function loop () {
ctx.clearRect(0, 0, canvasWidth, canvasHeight);
if (!needAnimate) return;
if (waveY < waveY_max) waveY += 1.5;
if (waveX < waveX_min) waveX = 0; else waveX -= 3;

ctx.globalCompositeOperation = 'source-over';
ctx.beginPath();
ctx.arc(canvasWidth/2, canvasHeight/2, canvasHeight/2, 0, Math.PI*2, true);
ctx.closePath();
ctx.fill();

ctx.globalCompositeOperation = 'source-in';
ctx.drawImage(waveImage, waveX, canvasHeight - waveY);

requestAnimationFrame(loop);
}
loop();
}

function start () {
if (!ctx) return init(start);
needAnimate = true;
setTimeout(function () {
if (needAnimate) animate();
}, 500);
}
function stop () {
needAnimate = false;
}
return {start: start, stop: stop};
}());
wave.start();