动手学Javascript（3）——HTML5模拟下雪

马上就是圣诞节，基于HTML5的Canvas写个网页动画，祝大家圣诞节快乐。

在该网页中动画中，用简单的模型模拟下雪的场景，其截屏效果如下图所示。如果你想看动画的动态效果，也可以到网页http://jsfiddle.net/zhedahht/2uD5x/1/ 查看。

雪花被简化成一个白色的圆形，并按照正弦曲线缓慢降落。这个模型虽然简单，但效果基本满足卡通动画的要求。代码如下：

$(document).ready(function () {    makeSnow("christmasSnow", "./Image/Christmas.jpg");});function makeSnow(canvasId, imagePath) {    var christmasSnow = new ChristmasSnow(canvasId, imagePath);        renderAndUpdate.christmasSnow = christmasSnow;    setInterval(renderAndUpdate, 15);}function renderAndUpdate() {    renderAndUpdate.christmasSnow.render();    renderAndUpdate.christmasSnow.update();}function ChristmasSnow(canvasId, imagePath) {    var snowElement = document.getElementById(canvasId);    this.canvasContext = snowElement.getContext("2d");        this.width = snowElement.clientWidth;    this.heigth = snowElement.clientHeight;        this.image = initImage(imagePath);    this.snow = initSnow(this.width, this.heigth);}function initImage(imagePath) {    var image = new Image();    image.src = imagePath;    return image;}function initSnow(width, height) {    var minRasius = 3,        maxRadius = 10,        minSpeedY = 1,        maxSpeedY = 3,        speedX = 0.05,        minAlpha = 0.5,        maxAlpha = 1.0,        minMoveX = 4,        maxMoveX = 18;    var snowSettings = new SnowSettings(minRasius, maxRadius, width, height, minSpeedY, maxSpeedY, speedX, minAlpha, maxAlpha, minMoveX, maxMoveX);        var snow = [];    var snowNumber = 200;    for(var i = 0; i < snowNumber; ++i) {        snow[i] = new Snow(snowSettings);    }        return snow;}ChristmasSnow.prototype.render = function() {    // render background image    this.canvasContext.drawImage(this.image, 0, 0);        // render snow    for(var i = 0; i < this.snow.length; ++i) {        this.snow[i].render(this.canvasContext);    }}ChristmasSnow.prototype.update = function() {    for(var i = 0; i < this.snow.length; ++i) {        this.snow[i].update();    }}function SnowSettings(minRadius, maxRadius, maxX, maxY, minSpeedY, maxSpeedY, speedX, minAlpha, maxAlpha, minMoveX, maxMoveX) {    this.minRadius = minRadius;    this.maxRadius = maxRadius;    this.maxX = maxX;    this.maxY = maxY;    this.speedX = speedX;    this.minSpeedY = minSpeedY;    this.maxSpeedY = maxSpeedY;    this.minAlpha = minAlpha;    this.maxAlpha = maxAlpha;    this.minMoveX = minMoveX;    this.maxMoveX = maxMoveX;}function Snow(snowSettings) {    this.snowSettings = snowSettings;        this.radius = randomInRange(snowSettings.minRadius, snowSettings.maxRadius);    this.initialX = Math.random() * snowSettings.maxX;    this.y = Math.random() * snowSettings.maxY;    this.speedY = randomInRange(snowSettings.minSpeedY, snowSettings.maxSpeedY);    this.speedX = snowSettings.speedX;    this.alpha = randomInRange(snowSettings.minAlpha, snowSettings.maxAlpha);    this.angle = Math.random(Math.PI * 2);    this.x = this.initialX + Math.sin(this.angle);    this.moveX = randomInRange(snowSettings.minMoveX, snowSettings.maxMoveX);}Snow.prototype.render = function(canvasContext) {    canvasContext.fillStyle = "rgba(255, 255, 255, " + this.alpha + ")";    canvasContext.beginPath();    canvasContext.arc(this.x, this.y, this.radius, 0, Math.PI * 2, true);    canvasContext.closePath();    canvasContext.fill(); }Snow.prototype.update = function() {    this.y += this.speedY;    if (this.y > this.snowSettings.maxY) {        this.y -= this.snowSettings.maxY;    }        this.angle += this.speedX;    if (this.angle > Math.PI * 2) {        this.angle -= Math.PI * 2;    }    this.x = this.initialX + this.moveX * Math.sin(this.angle);}function randomInRange(min, max) {    var random = Math.random() * (max - min) + min;    return random;}

如果您感兴趣，可以到如下链接下载源代码：

http://download.csdn.net/detail/haitaohe/6757563。