JS+canvas画布实现炫酷的旋转星空效果示例

本文实例讲述了js+canvas画布实现炫酷的旋转星空效果。分享给大家供大家参考，具体如下：

canvas是html5的新标签，其画布功能尤为强大。当然了canvas在ie10以下浏览器是不兼容的，所以呢为了特效肯定是牺牲一定的兼容性。这里呢，分享一个基于canvas开发的浩瀚星河插件，其实这个源代码是网上下载的，我把它整合了一下，重新封装一些参数提供更多的可改项。

首先引入两个javascript脚本，一个是jquery插件，另一个是封装好的cosmos_canvas.js

<script src="js/jquery-1.11.0.js" type="text/javascript" charset="utf-8"></script>
<script src="canvas/cosmos_canvas.js" type="text/javascript" charset="utf-8"></script>

html，当然如果浏览器不支持canvas的话，运行程序没效果，并显示“该浏览器不支持canvas”

<canvas id="starts">该浏览器不支持canvas</canvas>

cosmos_canvas.js脚本

function canvas(id,starscolor,starsamount,starsradius,movrange,speed,trailing){
  //宇宙特效
"use strict";
var canvas = document.getelementbyid(id),
 ctx = canvas.getcontext('2d'),
 w = canvas.width = window.innerwidth,
 h = canvas.height = window.innerheight,
 hue = starscolor,//230
 stars = [],
 count = 0,
 maxstars = starsamount;//星星数量
var canvas2 = document.createelement('canvas'),
 ctx2 = canvas2.getcontext('2d');
canvas2.width = 100;
canvas2.height = 100;
var half = canvas2.width / 2,
 gradient2 = ctx2.createradialgradient(half, half, 0, half, half, half);
gradient2.addcolorstop(0.025, '#ccc');
gradient2.addcolorstop(0.1, 'hsl(' + hue + ', 61%, 33%)');
gradient2.addcolorstop(0.25, 'hsl(' + hue + ', 64%, 6%)');
gradient2.addcolorstop(1, 'transparent');
ctx2.fillstyle = gradient2;
ctx2.beginpath();
ctx2.arc(half, half, half, 0, math.pi * 2);
ctx2.fill();
// end cache
function random(min, max) {
 if (arguments.length < 2) {
  max = min;
  min = 0;
 }
 if (min > max) {
  var hold = max;
  max = min;
  min = hold;
 }
 return math.floor(math.random() * (max - min + 1)) + min;
}
function maxorbit(x, y) {
 var max = math.max(x, y),
  diameter = math.round(math.sqrt(max * max + max * max));
 return diameter / movrange;
 //星星移动范围，值越大范围越小，
}
var star = function() {
 this.orbitradius = random(maxorbit(w, h));
 this.radius = random(starsradius, this.orbitradius) / 8;
 //星星半径大小
 this.orbitx = w / 2;
 this.orbity = h / 2;
 this.timepassed = random(0, maxstars);
 this.speed = random(this.orbitradius) / speed;
 //星星移动速度
 this.alpha = random(2, 10) / 10;
 count++;
 stars[count] = this;
}
star.prototype.draw = function() {
 var x = math.sin(this.timepassed) * this.orbitradius + this.orbitx,
  y = math.cos(this.timepassed) * this.orbitradius + this.orbity,
  twinkle = random(10);
 if (twinkle === 1 && this.alpha > 0) {
  this.alpha -= 0.05;
 } else if (twinkle === 2 && this.alpha < 1) {
  this.alpha += 0.05;
 }
 ctx.globalalpha = this.alpha;
 ctx.drawimage(canvas2, x - this.radius / 2, y - this.radius / 2, this.radius, this.radius);
 this.timepassed += this.speed;
}
for (var i = 0; i < maxstars; i++) {
 new star();
}
function animation() {
 ctx.globalcompositeoperation = 'source-over';
 ctx.globalalpha = trailing; //尾巴
 ctx.fillstyle = 'hsla(' + hue + ', 64%, 6%, 2)';
 ctx.fillrect(0, 0, w, h)
 ctx.globalcompositeoperation = 'lighter';
 for (var i = 1, l = stars.length; i < l; i++) {
  stars[i].draw();
 };
 window.requestanimationframe(animation);
}
animation();
}

调用方法：这里没写任何样式所以默认情况下是全屏效果

$(function(){
//canvas的id名，星星颜色(hsla的hue色调)，星星数量，星星半径比，星星移动范围(值越大范围越小)，星星移动速度(值越大速度越慢),星星拖尾效果(0~1值越小拖尾越明显)
canvas("starts",230,1000,60,2,50000,0.5);
});

效果：

然后我再加3个canvas，改些参数做效果对比吧

html

<canvas id="starts">该浏览器不支持canvas</canvas>
<canvas id="starts1">该浏览器不支持canvas</canvas>
<canvas id="starts2">该浏览器不支持canvas</canvas>
<canvas id="starts3">该浏览器不支持canvas</canvas>

javascript

$(function(){
  //canvas的id名，星星颜色(hsla的hue色调)，星星数量，星星半径比，星星移动范围(值越大范围越小)，星星移动速度(值越大速度越慢),星星拖尾效果(0~1值越小拖尾越明显)
  canvas("starts",230,1000,60,2,50000,0.5);
  canvas("starts1",160,800,70,2.5,55000,0.4);
  canvas("starts2",80,600,80,3,60000,0.3);
  canvas("starts3",0,400,90,3.5,65000,0.2);
  $("canvas").width($(window).width()/2);
  $("canvas").height($(window).height()/2);
  $("canvas").css("float","left");
});

就这样，四个浩瀚的宇宙出来了

更多关于javascript相关内容还可查看本站专题：《javascript+html5特效与技巧汇总》、《javascript图形绘制技巧总结》、《javascript错误与调试技巧总结》、《javascript数据结构与算法技巧总结》、《javascript遍历算法与技巧总结》及《javascript数学运算用法总结》

希望本文所述对大家javascript程序设计有所帮助。