canvas繪制流星效果
偶然看到一篇用canvas繪制流星雨，試了試效果還不錯
<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <title>一起來看流星雨</title> <script> var context; var arr = new Array(); var starCount = 800; var rains = new Array(); var rainCount = 20; //初始化畫布及context function init() { //獲取canvas var stars = document.getElementById("stars"); windowWidth = window.innerWidth; //當前的窗口的高度 stars.width = windowWidth; stars.height = window.innerHeight; //獲取context context = stars.getContext("2d"); } //創建一個星星對象 var Star = function () { this.x = windowWidth * Math.random();//橫坐標 this.y = 5000 * Math.random();//縱坐標 this.text = ".";//文本 this.color = "white";//顏色 //產生隨機顏色 this.getColor = function () { var _r = Math.random(); if (_r < 0.5) { this.color = "#333"; } else { this.color = "white"; } } //初始化 this.init = function () { this.getColor(); } //繪制 this.draw = function () { context.fillStyle = this.color; context.fillText(this.text, this.x, this.y); } } //畫月亮 function drawMoon() { var moon = new Image(); moon.src = "./images/moon.jpg" context.drawImage(moon, -5, -10); } //頁面加載的時候 window.onload = function () { init(); //畫星星 for (var i = 0; i < starCount; i++) { var star = new Star(); star.init(); star.draw(); arr.push(star); } //畫流星 for (var i = 0; i < rainCount; i++) { var rain = new MeteorRain(); rain.init(); rain.draw(); rains.push(rain); } drawMoon();//繪制月亮 playStars();//繪制閃動的星星 playRains();//繪制流星 } //星星閃起來 function playStars() { for (var n = 0; n < starCount; n++) { arr[n].getColor(); arr[n].draw(); } setTimeout("playStars()", 100); } /*流星雨開始*/ var MeteorRain = function () { this.x = -1; this.y = -1; this.length = -1;//長度 this.angle = 30; //傾斜角度 this.width = -1;//寬度 this.height = -1;//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 this.color1 = "";//流星的色彩 this.color2 = ""; //流星的色彩 /****************初始化函數********************/ this.init = function () //初始化 { this.getPos(); this.alpha = 1;//透明度 this.getRandomColor(); //最小長度，最大長度 var x = Math.random() * 80 + 150; this.length = Math.ceil(x); // x = Math.random()*10+30; this.angle = 30; //流星傾斜角 x = Math.random() + 0.5; this.speed = Math.ceil(x); //流星的速度 var cos = Math.cos(this.angle * 3.14 / 180); var sin = Math.sin(this.angle * 3.14 / 180); this.width = this.length * cos; //流星所占寬度 this.height = this.length * sin;//流星所占高度 this.offset_x = this.speed * cos; this.offset_y = this.speed * sin; } /**************獲取隨機顏色函數*****************/ this.getRandomColor = function () { var a = Math.ceil(255 - 240 * Math.random()); //中段顏色 this.color1 = "rgba(" + a + "," + a + "," + a + ",1)"; //結束顏色 this.color2 = "#090723"; } /***************重新計算流星坐標的函數******************/ this.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; } /*****************獲取隨機坐標的函數*****************/ this.getPos = function () // { //橫坐標200--1200 this.x = Math.random() * window.innerWidth; //窗口高度 //縱坐標小於600 this.y = Math.random() * window.innerHeight; //窗口寬度 } /****繪制流星***************************/ this.draw = function () //繪制一個流星的函數 { context.save(); context.beginPath(); context.lineWidth = 1; //寬度 context.globalAlpha = this.alpha; //設置透明度 //創建橫向漸變顏色,起點坐標至終點坐標 var line = context.createLinearGradient(this.x, this.y, this.x + this.width, this.y - this.height); //分段設置顏色 line.addColorStop(0, "white"); line.addColorStop(0.3, this.color1); line.addColorStop(0.6, this.color2); 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(); } this.move = function () { //清空流星像素 var x = this.x + this.width - this.offset_x; var y = this.y - this.height; context.clearRect(x - 3, y - 3, this.offset_x + 5, this.offset_y + 5); // context.strokeStyle="red"; // context.strokeRect(x,y-1,this.offset_x+1,this.offset_y+1); //重新計算位置，往左下移動 this.countPos(); //透明度增加 this.alpha -= 0.002; //重繪 this.draw(); } } //繪制流星 function playRains() { for (var n = 0; n < rainCount; n++) { var rain = rains[n]; rain.move();//移動 if (rain.y > window.innerHeight) {//超出界限后重來 context.clearRect(rain.x, rain.y - rain.height, rain.width, rain.height); rains[n] = new MeteorRain(); rains[n].init(); } } setTimeout("playRains()", 2); } /*流星雨結束*/ </script> <style type="text/css"> body { background-color: #090723; } body, html { width: 100%; height: 100%; overflow: hidden; } </style> </head> <body> <canvas id="stars"></canvas> </body> </html>