本文主要是介绍js实现随机移动的萤火虫，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
知识点：3次贝塞尔曲线
请在这里查看示例 ☞ firefly示例
html:
<!DOCTYPE html>
<html lang="en">
<head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1, minimum-scale=1, maximum-scale=1, user-scalable=no"> <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"/> <script type="text/javascript" src="../js/jquery-1.11.3.min.js"></script> <script type="text/javascript" src="js/fly.js"></script> <title>demo</title> <style> * { margin: 0; padding: 0; } body, html { width: 100%; height: 100%; } .cav { position: absolute; top: 0; left: 0; } </style>
</head>
<body> <canvas class="cav"></canvas>
<script> </script>
</body>
</html>;$(function() { var $cav = $('.cav'); var $cavParent = $cav.parent(); var cav = $cav[0].getContext('2d'), backColor = '#f7fafc',//背景颜色 frontColor = 'rgba(200, 200, 200, .8)',//点颜色 overPoint = -10000, mouseArr = [overPoint, overPoint, 200];//鼠标位置和极限半径 $('body').css('background', backColor);var cavW = $cavParent.width(), cavH = $cavParent.height(), dotArr = [], bezierArr = [], num = 20,// 点的个数 ran = 500; step = 500; $cav.attr({ 'width': cavW, 'height': cavH, }).css({ 'background': backColor, }); $cav.on('mousemove', function(e) { mouseArr[0] = e.offsetX; mouseArr[1] = e.offsetY; }); $cav.on('mouseout', function(e) { mouseArr[0] = overPoint; mouseArr[1] = overPoint; }); //生成随机点 for(var i=0; i<num; i++) { var cavL1 = Math.random()*cavW, cavT1 = Math.random()*cavH, cavL2 = Math.random()*cavW, cavT2 = Math.random()*cavH, cavL3 = Math.random()*cavW, cavT3 = Math.random()*cavH, cavL4 = Math.random()*cavW, cavT4 = Math.random()*cavH, cavO = Math.random(),//透明度 cavR = cavO*8+2,//尺寸 cavD = parseInt(Math.random()*ran)+step;//点的个数 cavT = 0;//自身计数器 dotArr[i] = [[cavL1, cavT1]/*0*/, [cavL2, cavT2]/*1*/, [cavL3, cavT3]/*2*/, [cavL4, cavT4]/*3*/, cavO/*4*/, cavR/*5*/, cavD/*6*/, cavT/*7*/];//存储坐标 var cp = [new Point2D(dotArr[i][0][0], dotArr[i][0][1]), new Point2D(dotArr[i][1][0], dotArr[i][1][1]), new Point2D(dotArr[i][2][0], dotArr[i][2][1]), new Point2D(dotArr[i][3][0], dotArr[i][3][1])]; var numberOfPoints=dotArr[i][6]; var curve=[]; ComputeBezier(cp, numberOfPoints, curve); bezierArr[i] = curve; } setInterval(function() { cav.clearRect(0, 0, cavW, cavH); //移动 for(var i=0; i<num; i++) { if(dotArr[i][7] >= dotArr[i][6]) {//走到最后一个点 var cavL1 = Math.random()*cavW, cavT1 = Math.random()*cavH, cavL2 = Math.random()*cavW, cavT2 = Math.random()*cavH, cavL3 = Math.random()*cavW, cavT3 = Math.random()*cavH, cavL4 = Math.random()*cavW, cavT4 = Math.random()*cavH, cavO = Math.random(),//透明度 cavR = cavO*8+2,//尺寸 cavD = parseInt(Math.random()*ran)+step;//点的个数 cavT = 0;//自身计数器 dotArr[i] = [[bezierArr[i][dotArr[i][6]-1].x, bezierArr[i][dotArr[i][6]-1].y]/*0*/, [cavL2, cavT2]/*1*/, [cavL3, cavT3]/*2*/, [cavL4, cavT4]/*3*/, dotArr[i][4]/*4*/, dotArr[i][5]/*5*/, cavD/*6*/, cavT/*7*/];//存储坐标 var cp = [new Point2D(dotArr[i][0][0], dotArr[i][0][1]), new Point2D(dotArr[i][1][0], dotArr[i][1][1]), new Point2D(dotArr[i][2][0], dotArr[i][2][1]), new Point2D(dotArr[i][3][0], dotArr[i][3][1])]; var numberOfPoints=dotArr[i][6]; var curve=[]; ComputeBezier(cp, numberOfPoints, curve); bezierArr[i] = curve; }else { // 和鼠标交互 if(Math.pow(bezierArr[i][dotArr[i][7]].x-mouseArr[0], 2)+Math.pow(bezierArr[i][dotArr[i][7]].y-mouseArr[1], 2) <= Math.pow(mouseArr[2], 2)) { cav.beginPath(); var globalAlpha = 1-Math.sqrt(Math.pow(bezierArr[i][dotArr[i][7]].x-mouseArr[0], 2)+Math.pow(bezierArr[i][dotArr[i][7]].y-mouseArr[1], 2))/100/2; globalAlpha = globalAlpha<0?0:globalAlpha; cav.globalAlpha = globalAlpha; cav.strokeStyle = frontColor; cav.lineTo(mouseArr[0],mouseArr[1]); cav.lineTo(bezierArr[i][dotArr[i][7]].x, bezierArr[i][dotArr[i][7]].y); cav.stroke(); } // 点与点交互 for(var j=0; j<num; j++) { if(i!=j && dotArr[j][7] < dotArr[j][6]) {//走到最后一个点且不是同一个点 if(Math.pow(bezierArr[i][dotArr[i][7]].x-bezierArr[j][dotArr[j][7]].x, 2)+Math.pow(bezierArr[i][dotArr[i][7]].y-bezierArr[j][dotArr[j][7]].y, 2) <= Math.pow(mouseArr[2], 2)) { cav.beginPath(); var globalAlpha = 1-Math.sqrt(Math.pow(bezierArr[i][dotArr[i][7]].x-bezierArr[j][dotArr[j][7]].x, 2)+Math.pow(bezierArr[i][dotArr[i][7]].y-bezierArr[j][dotArr[j][7]].y, 2))/100/2; globalAlpha = globalAlpha<0?0:globalAlpha; cav.globalAlpha = globalAlpha; cav.strokeStyle = frontColor; cav.lineTo(bezierArr[j][dotArr[j][7]].x,bezierArr[j][dotArr[j][7]].y); cav.lineTo(bezierArr[i][dotArr[i][7]].x, bezierArr[i][dotArr[i][7]].y); cav.stroke(); } } } cav.beginPath(); cav.globalAlpha = dotArr[i][4]*.6; cav.fillStyle = frontColor; cav.arc(bezierArr[i][dotArr[i][7]].x, bezierArr[i][dotArr[i][7]].y, dotArr[i][5], 0, 2*Math.PI); cav.fill(); } dotArr[i][7] += 1; } }, 20); function Point2D(x, y){ this.x=x||0.0; this.y=y||0.0; } function PointOnCubicBezier(cp, t) {//cp为4个Point2D点，0<=t<=1 var ax, bx, cx; var ay, by, cy; var tSquared, tCubed; var result = new Point2D; //计算多项式系数 cx = 3.0 * (cp[1].x - cp[0].x); bx = 3.0 * (cp[2].x - cp[1].x) - cx; ax = cp[3].x - cp[0].x - cx - bx; cy = 3.0 * (cp[1].y - cp[0].y); by = 3.0 * (cp[2].y - cp[1].y) - cy; ay = cp[3].y - cp[0].y - cy - by; //计算位于参数值t的曲线点 tSquared = t * t; tCubed = tSquared * t; result.x = (ax * tCubed) + (bx * tSquared) + (cx * t) + cp[0].x; result.y = (ay * tCubed) + (by * tSquared) + (cy * t) + cp[0].y; return result; } //ComputeBezier以控制点cp所产生的曲线点，填入Point2D的阵列，必须分配足够的记忆体，其<sizeof(Point2D) numberOfPoints> function ComputeBezier(cp, numberOfPoints, curve) { var dt; var i; dt = 1.0 / ( numberOfPoints - 1 ); for( i = 0; i < numberOfPoints; i++) curve[i] = PointOnCubicBezier( cp, i*dt ); }
});
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