最近給公司網站banner做了流星特效，踩了一些坑，在這裡mark下。
(function () {
var context;//畫布上下文
var boundaryHeight;//畫布高，邊界值
var boundaryWidth;//畫布寬，邊界值
var starArr = [];
var meteorArr = [];
var STAR_COUNT = 500;//星星數，常量
var METEOR_COUNT = 4;//流星數，常量
var METEOR_SEPARATE = 300; //流星之間間隔，常量
var meteorCoordinateArr = [];//存所有流星的座標陣列
var playMeteorTimeout;
var playStarsTimeout;
//初始化畫布及context
function init(container) {
starArr = [];
meteorArr = [];
var canvas = document.createElement("canvas");
container.appendChild(canvas);
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
boundaryHeight = canvas.height;
boundaryWidth = canvas.width;
//獲取context
context = canvas.getContext("2d");
context.fillStyle = "black";
//畫星星
for (var i = 0; i < STAR_COUNT; i++) {
var star = new Star();
star.init();
star.draw();
starArr.push(star);
}
//畫流星
for (var j = 0; j < METEOR_COUNT; j++) {
var rain = new MeteorRain();
rain.init(j);
rain.draw();
meteorArr.push(rain);
}
playStars();//星星動起來
playMeteor();//流星動起來
}
//建立一個星星物件
var Star = function () {
this.x = boundaryWidth * Math.random();//橫座標
this.y = boundaryHeight * Math.random();//縱座標
this.color = "";//星星顏色
};
Star.prototype = {
constructor: Star,
//初始化
init: function () {
this.getColor();
},
//產生隨機顏色
getColor: function () {
var _randomNum = Math.random();
if (_randomNum < 0.5) {
this.color = "gray";
}
else {
this.color = "white";
}
},
//繪製
draw: function () {
context.beginPath();
//畫圓點
context.arc(this.x, this.y, 0.05, 0, 2 * Math.PI);
context.strokeStyle = this.color;
context.stroke();
context.closePath();
}
}
//星星閃起來
function playStars() {
for (var n = 0; n < STAR_COUNT; n++) {
starArr[n].getColor();
starArr[n].draw();
}
clearTimeout(playStarsTimeout);
playStarsTimeout = setTimeout(playStars, 200);
}
//建立一個流星物件
var MeteorRain = function () {
this.x = -1;//流星的橫座標
this.y = -1;//流星的縱座標
this.length = -1;//流星的長度
this.angle = 30; //傾斜角度
this.width = -1;//流星所佔寬度，及矩形的寬度
this.height = -1;//流星所佔高度，及矩形的高度
this.speed = 1;//速度
this.offset_x = -1;//橫軸移動偏移量
this.offset_y = -1;//縱軸移動偏移量
this.alpha = 1; //透明度
};
MeteorRain.prototype = {
constructor: MeteorRain,
//初始化
init: function (i) {
this.alpha = 1;//透明度
this.angle = 30; //流星傾斜角
this.speed = Math.ceil(Math.random() + 0.5); //流星的速度
var x = Math.random() * 80 + 180;
var cos = Math.cos(this.angle * 3.14 / 180);
var sin = Math.sin(this.angle * 3.14 / 180) ;
this.length = Math.ceil(x);//流星長度
this.width = this.length * cos; //流星所佔寬度，及矩形的寬度
this.height = this.length * sin; //流星所佔高度，及矩形的高度
this.offset_x = this.speed * cos * 3.5;
this.offset_y = this.speed * sin * 3.5;
this.getPos(i);
},
//計算流星座標
countPos: function () {
//往左下移動,x減少，y增加
this.x = this.x - this.offset_x;
this.y = this.y + this.offset_y;
},
//獲取隨機座標
getPos: function (i) {
_this = this;
function getCoordinate() {
_this.x = Math.random() * boundaryWidth; //x座標
for (var k = 0; k < meteorCoordinateArr.length; k++) {
if (Math.abs(_this.x - meteorCoordinateArr[k]) < METEOR_SEPARATE) { //這裡如果流星之間距離過小，會把其他流星隔斷，嚴重影響效果。
return getCoordinate();
}
}
meteorCoordinateArr[i] = _this.x;
}
getCoordinate();
this.y = 0.2 * boundaryHeight; //y座標
},
//畫流星
draw: function () {
context.save();
context.beginPath();
context.lineWidth = 2.5; //寬度
context.globalAlpha = this.alpha; //設定透明度
//建立橫向漸變顏色,起點座標至終點座標
var line = context.createLinearGradient(this.x, this.y, this.x + this.width, this.y - this.height);
//分段設定顏色
line.addColorStop(0, "rgba(255, 255, 255, 1)");
line.addColorStop(1, "rgba(255, 255,255 , 0)");
if (this.alpha < 0 ) {
this.alpha = -this.alpha;
}
//填充
context.strokeStyle = line;
//起點
context.moveTo(this.x, this.y);
//終點
context.lineTo(this.x + this.width, this.y - this.height);
context.closePath();
context.stroke();
context.restore();
},
move: function () {
var x = this.x + this.width - this.offset_x;
var y = this.y - this.height;
this.alpha -= 0.002;
//重新計算位置，往左下移動
this.countPos();
if (this.alpha <= 0)="" {="" this.alpha="0;" }="" else="" if(this.alpha=""> 1) {
this.alpha = 1;
}
//畫一個矩形去清空流星
context.clearRect(this.x - this.offset_x, y, this.width + this.offset_x, this.height);
//重繪
this.draw();
}
}
//流星動起來
function playMeteor() {
for (var n = 0; n < METEOR_COUNT; n++) {
var rain = meteorArr[n];
rain.move();//移動
if (rain.y > boundaryHeight + 100) {//超出界限後重來
context.clearRect(rain.x, rain.y - rain.height, rain.width, rain.height);
meteorCoordinate[n] = 0;//清空座標陣列具體流星的座標
meteorArr[n] = new MeteorRain(n);
meteorArr[n].init(n);
}
}
clearTimeout(playMeteorTimeout);
playMeteorTimeout = setTimeout(playMeteor, 5);
}
//初始化
init(document.getElementsByTagName("body")[0]);
}()); 複製程式碼