出不来落雪的效果呢，代码和老师的一样呢
/**
* 雪花
* canvas版
*/
$(function() {
/**
* 雪球
* @param {[type]} elementName [description]
*/
function Snowflake(elementName) {
var config = {};
var snowElement = document.getElementById(elementName)
var canvasContext = snowElement.getContext("2d");
var width = config.clientWidth;
var height = config.clientHeight;
//canvas尺寸修正
snowElement.width = width;
snowElement.height = height;
//构建雪球的数量
var snowNumber = 50;
//构建雪球对象
var snowArrObjs = initSnow(snowNumber, width, height);
var snowArrNum = snowArrObjs.length;
/**
* 绘制页面
* @return {[type]} [description]
*/
var render = function() {
//清理之前的矩形数据
canvasContext.clearRect(0, 0, width, height);
for (var i = 0; i < snowArrNum; ++i) {
snowArrObjs[i].render(canvasContext);
}
}
/**
* 更新雪花
* @return {[type]} [description]
*/
var update = function() {
for (var i = 0; i < snowArrNum; ++i) {
snowArrObjs[i].update();
}
}
/**
* 绘制与更新
* @return {[type]} [description]
*/
var renderAndUpdate = function() {
render();
update();
requestAnimationFrame(renderAndUpdate);
}
renderAndUpdate();
}
function initSnow(snowNumber, width, height) {
//雪球参数
var options = {
//雪球的半球距离
minRadius: 3,
maxRadius: 10,
// 运动的范围区域
maxX: width,
maxY: height,
//速率
minSpeedY: 0.05,
maxSpeedY: 2,
speedX: 0.05,
//滤镜
minAlpha: 0.5,
maxAlpha: 1.0,
minMoveX: 4,
maxMoveX: 18
}
var snowArr = [];
for (var i = 0; i < snowNumber; ++i) {
snowArr[i] = new Snow(options);
}
return snowArr;
}
/**
* 雪球类
*/
function Snow(snowSettings) {
this.snowSettings = snowSettings;
this.radius = randomInRange(snowSettings.minRadius, snowSettings.maxRadius);
//初始的x位置
this.initialX = Math.random() * snowSettings.maxX;
this.y = -(Math.random() * 500);
//运行的速率
this.speedY = randomInRange(snowSettings.minSpeedY, snowSettings.maxSpeedY);
this.speedX = snowSettings.speedX;
//滤镜
this.alpha = randomInRange(snowSettings.minAlpha, snowSettings.maxAlpha);
//角度.默认是360
this.angle = Math.random(Math.PI * 2);
//运行的距离
this.x = this.initialX + Math.sin(this.angle);
//x移动距离
this.moveX = randomInRange(snowSettings.minMoveX, snowSettings.maxMoveX);
}
/**
* 绘制雪球
* @param {[type]} canvasContext [description]
* @return {[type]} [description]
*/
Snow.prototype.render = function(canvasContext) {
//清除路径
//开始一个画布中的一条新路径（或者子路径的一个集合）
canvasContext.beginPath();
//用来填充路径的当前的颜色，白色的雪球
canvasContext.fillStyle = "rgba(255, 255, 255, " + this.alpha + ")";
//一个中心点和半径，为一个画布的当前子路径添加一条弧线
//坐标，圆，沿着圆指定弧的开始点和结束点的一个角度
//弧沿着圆周的逆时针方向（TRUE）还是顺时针方向（FALSE）遍历
canvasContext.arc(this.x, this.y, this.radius, 0, Math.PI * 2, true);
//关闭子路径
canvasContext.closePath();
//fill() 方法使用 fillStyle 属性所指定的颜色、渐变和模式来填充当前路径
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);
}
/**
* 随机处理
* @param {[type]} min [description]
* @param {[type]} max [description]
* @return {[type]} [description]
*/
function randomInRange(min, max) {
var random = Math.random() * (max - min) + min;
return random;
}
Snowflake("snowflake")
})
