Html5 Canvas+JavaScript物理引擎实例

Html5 Canvas+JavaScript物理引擎实例 canvas绘制蜘蛛和js物理引擎模拟行为的实现

<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="Generator" content="EditPlus®">
<meta name="Author" content="">
<meta name="Keywords" content="">
<meta name="Description" content="">
<title>Document</title>
<script type="text/javascript" src="http://sandbox.runjs.cn/uploads/rs/146/73fi1rab/objects.js"></script>
<script type="text/javascript" src="http://sandbox.runjs.cn/uploads/rs/146/73fi1rab/verlet.js"></script>
<script type="text/javascript" src="http://sandbox.runjs.cn/uploads/rs/146/73fi1rab/constraint.js"></script>
<script type="text/javascript" src="http://sandbox.runjs.cn/uploads/rs/146/73fi1rab/vec2.js"></script>

<canvas id="scratch" style="width: 800px; height: 500px;"></canvas>
<style>@font-face {
font-family: 'Libre Baskerville';
font-style: normal;
font-weight: 400;
src: local('Libre Baskerville'), local('LibreBaskerville-Regular'), url(http://themes.googleusercontent.com/static/fonts/librebaskerville/v1/pR0sBQVcY0JZc_ciXjFsK5Rby8KfwQsaipLBqMCVNtM.woff) format('woff');
}
@font-face {
font-family: 'Libre Baskerville';
font-style: normal;
font-weight: 700;
src: local('Libre Baskerville Bold'), local('LibreBaskerville-Bold'), url(http://themes.googleusercontent.com/static/fonts/librebaskerville/v1/kH7K4InNTm7mmOXXjrA5vz8SLKRGgamuUl1hIefMyNI.woff) format('woff');
}
@font-face {
font-family: 'Libre Baskerville';
font-style: italic;
font-weight: 400;
src: local('Libre Baskerville Italic'), local('LibreBaskerville-Italic'), url(http://themes.googleusercontent.com/static/fonts/librebaskerville/v1/QHIOz1iKF3bIEzRdDFaf5dgliI79_bmRXH6crmREtCo.woff) format('woff');
}

body {
background: #e4e6e8;
background: -moz-linear-gradient(top, #ffffff 0%, #e4e8ee 20%, #e4e8ee 80%, #ffffff 100%); /* FF3.6+ */
background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,#ffffff), color-stop(20%,#e4e8ee), color-stop(80%,#e4e8ee), color-stop(100%,#ffffff)); /* Chrome,Safari4+ */
background: -webkit-linear-gradient(top, #ffffff 0%,#e4e8ee 20%,#e4e8ee 80%,#ffffff 100%); /* Chrome10+,Safari5.1+ */
background: -o-linear-gradient(top, #ffffff 0%,#e4e8ee 20%,#e4e8ee 80%,#ffffff 100%); /* Opera 11.10+ */
background: -ms-linear-gradient(top, #ffffff 0%,#e4e8ee 20%,#e4e8ee 80%,#ffffff 100%); /* IE10+ */
background: linear-gradient(to bottom, #ffffff 0%,#e4e8ee 20%,#e4e8ee 80%,#ffffff 100%); /* W3C */
filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#ffffff', endColorstr='#ffffff',GradientType=0 ); /* IE6-9 */

color: #969ba3;
font-family: "Libre Baskerville", sans-serif;
font-weight: 400;
line-height: 1.2em;
}

canvas {
display: block;
margin: 34px auto;
background: #fff;
box-shadow: 2px 2px 8px 0px rgba(0,0,0,0.1);
}</style>
       <script> VerletJS.prototype.spider = function(origin) {
  var i;
  var legSeg1Stiffness = 0.99;
  var legSeg2Stiffness = 0.99;
  var legSeg3Stiffness = 0.99;
  var legSeg4Stiffness = 0.99;

  var joint1Stiffness = 1;
  var joint2Stiffness = 0.4;
  var joint3Stiffness = 0.9;

var bodyStiffness = 1;
var bodyJointStiffness = 1;

var composite = new this.Composite();
composite.legs = [];

  composite.thorax = new Particle(origin);
  composite.head = new Particle(origin.add(new Vec2(0,-5)));
  composite.abdomen = new Particle(origin.add(new Vec2(0,10)));

  composite.particles.push(composite.thorax);
  composite.particles.push(composite.head);
  composite.particles.push(composite.abdomen);

composite.constraints.push(new DistanceConstraint(composite.head, composite.thorax, bodyStiffness));

composite.constraints.push(new DistanceConstraint(composite.abdomen, composite.thorax, bodyStiffness));
composite.constraints.push(new AngleConstraint(composite.abdomen, composite.thorax, composite.head, 0.4));

  // 蜘蛛腿
  for (i=0;i<4;++i) {
   composite.particles.push(new Particle(composite.particles[0].pos.add(new Vec2(3,(i-1.5)*3))));
   composite.particles.push(new Particle(composite.particles[0].pos.add(new Vec2(-3,(i-1.5)*3))));

var len = composite.particles.length;

composite.constraints.push(new DistanceConstraint(composite.particles[len-2], composite.thorax, legSeg1Stiffness));
composite.constraints.push(new DistanceConstraint(composite.particles[len-1], composite.thorax, legSeg1Stiffness));

   var lenCoef = 1;
   if (i == 1 || i == 2)
    lenCoef = 0.7;
   else if (i == 3)
    lenCoef = 0.9;

composite.particles.push(new Particle(composite.particles[len-2].pos.add((new Vec2(20,(i-1.5)*30)).normal().mutableScale(20*lenCoef))));
composite.particles.push(new Particle(composite.particles[len-1].pos.add((new Vec2(-20,(i-1.5)*30)).normal().mutableScale(20*lenCoef))));

   len = composite.particles.length;
   composite.constraints.push(new DistanceConstraint(composite.particles[len-4], composite.particles[len-2], legSeg2Stiffness));
   composite.constraints.push(new DistanceConstraint(composite.particles[len-3], composite.particles[len-1], legSeg2Stiffness));

composite.particles.push(new Particle(composite.particles[len-2].pos.add((new Vec2(20,(i-1.5)*50)).normal().mutableScale(20*lenCoef))));
composite.particles.push(new Particle(composite.particles[len-1].pos.add((new Vec2(-20,(i-1.5)*50)).normal().mutableScale(20*lenCoef))));

   len = composite.particles.length;
   composite.constraints.push(new DistanceConstraint(composite.particles[len-4], composite.particles[len-2], legSeg3Stiffness));
   composite.constraints.push(new DistanceConstraint(composite.particles[len-3], composite.particles[len-1], legSeg3Stiffness));

   var rightFoot = new Particle(composite.particles[len-2].pos.add((new Vec2(20,(i-1.5)*100)).normal().mutableScale(12*lenCoef)));
   var leftFoot = new Particle(composite.particles[len-1].pos.add((new Vec2(-20,(i-1.5)*100)).normal().mutableScale(12*lenCoef)))
   composite.particles.push(rightFoot);
   composite.particles.push(leftFoot);

composite.legs.push(rightFoot);
composite.legs.push(leftFoot);

   len = composite.particles.length;
   composite.constraints.push(new DistanceConstraint(composite.particles[len-4], composite.particles[len-2], legSeg4Stiffness));
   composite.constraints.push(new DistanceConstraint(composite.particles[len-3], composite.particles[len-1], legSeg4Stiffness));

composite.constraints.push(new AngleConstraint(composite.particles[len-6], composite.particles[len-4], composite.particles[len-2], joint3Stiffness));
composite.constraints.push(new AngleConstraint(composite.particles[len-6+1], composite.particles[len-4+1], composite.particles[len-2+1], joint3Stiffness));

composite.constraints.push(new AngleConstraint(composite.particles[len-8], composite.particles[len-6], composite.particles[len-4], joint2Stiffness));
composite.constraints.push(new AngleConstraint(composite.particles[len-8+1], composite.particles[len-6+1], composite.particles[len-4+1], joint2Stiffness));

composite.constraints.push(new AngleConstraint(composite.particles[0], composite.particles[len-8], composite.particles[len-6], joint1Stiffness));
composite.constraints.push(new AngleConstraint(composite.particles[0], composite.particles[len-8+1], composite.particles[len-6+1], joint1Stiffness));

   composite.constraints.push(new AngleConstraint(composite.particles[1], composite.particles[0], composite.particles[len-8], bodyJointStiffness));
   composite.constraints.push(new AngleConstraint(composite.particles[1], composite.particles[0], composite.particles[len-8+1], bodyJointStiffness));
  }

this.composites.push(composite);
return composite;
}

VerletJS.prototype.spiderweb = function(origin, radius, segments, depth) {
  var stiffness = 0.6;
  var tensor = 0.3;
  var stride = (2*Math.PI)/segments;
  var n = segments*depth;
  var radiusStride = radius/n;
  var i, c;

var composite = new this.Composite();

  // 粒子系统
  for (i=0;i<n;++i) {
   var theta = i*stride + Math.cos(i*0.4)*0.05 + Math.cos(i*0.05)*0.2;
   var shrinkingRadius = radius - radiusStride*i + Math.cos(i*0.1)*20;

   var offy = Math.cos(theta*2.1)*(radius/depth)*0.2;
   composite.particles.push(new Particle(new Vec2(origin.x + Math.cos(theta)*shrinkingRadius, origin.y + Math.sin(theta)*shrinkingRadius + offy)));
  }

for (i=0;i<segments;i+=4)
composite.pin(i);

  // 约束
  for (i=0;i<n-1;++i) {
   // 邻接
   composite.constraints.push(new DistanceConstraint(composite.particles[i], composite.particles[i+1], stiffness));

   // 跨环
   var off = i + segments;
   if (off < n-1)
    composite.constraints.push(new DistanceConstraint(composite.particles[i], composite.particles[off], stiffness));
   else
    composite.constraints.push(new DistanceConstraint(composite.particles[i], composite.particles[n-1], stiffness));
  }

composite.constraints.push(new DistanceConstraint(composite.particles[0], composite.particles[segments-1], stiffness));

for (c in composite.constraints)
composite.constraints[c].distance *= tensor;

this.composites.push(composite);
return composite;
}

function shuffle(o) {
for(var j, x, i = o.length; i; j = parseInt(Math.random() * i), x = o[--i], o[i] = o[j], o[j] = x);
return o;
}

VerletJS.prototype.crawl = function(leg) {

var stepRadius = 100;
var minStepRadius = 35;

var spiderweb = this.composites[0];
var spider = this.composites[1];

var theta = spider.particles[0].pos.angle2(spider.particles[0].pos.add(new Vec2(1,0)), spider.particles[1].pos);

var boundry1 = (new Vec2(Math.cos(theta), Math.sin(theta)));
var boundry2 = (new Vec2(Math.cos(theta+Math.PI/2), Math.sin(theta+Math.PI/2)));

var flag1 = leg < 4 ? 1 : -1;
var flag2 = leg%2 == 0 ? 1 : 0;

var paths = [];

  var i;
  for (i in spiderweb.particles) {
   if (
    spiderweb.particles[i].pos.sub(spider.particles[0].pos).dot(boundry1)*flag1 >= 0
    && spiderweb.particles[i].pos.sub(spider.particles[0].pos).dot(boundry2)*flag2 >= 0
   ) {
    var d2 = spiderweb.particles[i].pos.dist2(spider.particles[0].pos);

if (!(d2 >= minStepRadius*minStepRadius && d2 <= stepRadius*stepRadius))
continue;

    if (!leftFoot)
     paths.push(spiderweb.particles[i]);
   }
  }

  for (i in spider.constraints) {
   if (spider.constraints[i] instanceof DistanceConstraint && spider.constraints[i].a == spider.legs[leg]) {
    spider.constraints.splice(i, 1);
    break;
   }
  }

  if (paths.length > 0) {
   shuffle(paths);
   spider.constraints.push(new DistanceConstraint(spider.legs[leg], paths[0], 1, 0));
  }
}

window.onload = function() {
var canvas = document.getElementById("scratch");

  // canvas
  var width = parseInt(canvas.style.width);
  var height = parseInt(canvas.style.height);

  // 视网膜
  var dpr = window.devicePixelRatio || 1;
  canvas.width = width*dpr;
  canvas.height = height*dpr;
  canvas.getContext("2d").scale(dpr, dpr);

// 模拟
var sim = new VerletJS(width, height, canvas);

// 实体
var spiderweb = sim.spiderweb(new Vec2(width/2,height/2), Math.min(width, height)/2, 20, 7);

var spider = sim.spider(new Vec2(width/2,-300));

  spiderweb.drawParticles = function(ctx, composite) {
   var i;
   for (i in composite.particles) {
    var point = composite.particles[i];
    ctx.beginPath();
    ctx.arc(point.pos.x, point.pos.y, 1.3, 0, 2*Math.PI);
    ctx.fillStyle = "#2dad8f";
    ctx.fill();
   }
  }

spider.drawConstraints = function(ctx, composite) {
var i;

   ctx.beginPath();
   ctx.arc(spider.head.pos.x, spider.head.pos.y, 4, 0, 2*Math.PI);
   ctx.fillStyle = "#000";
   ctx.fill();

   ctx.beginPath();
   ctx.arc(spider.thorax.pos.x, spider.thorax.pos.y, 4, 0, 2*Math.PI);
   ctx.fill();

   ctx.beginPath();
   ctx.arc(spider.abdomen.pos.x, spider.abdomen.pos.y, 8, 0, 2*Math.PI);
   ctx.fill();

   for (i=3;i<composite.constraints.length;++i) {
    var constraint = composite.constraints[i];
    if (constraint instanceof DistanceConstraint) {
     ctx.beginPath();
     ctx.moveTo(constraint.a.pos.x, constraint.a.pos.y);
     ctx.lineTo(constraint.b.pos.x, constraint.b.pos.y);

     // 把腿
     if (
      (i >= 2 && i <= 4)
      || (i >= (2*9)+1 && i <= (2*9)+2)
      || (i >= (2*17)+1 && i <= (2*17)+2)
      || (i >= (2*25)+1 && i <= (2*25)+2)
     ) {
      ctx.save();
      constraint.draw(ctx);
      ctx.strokeStyle = "#000";
      ctx.lineWidth = 3;
      ctx.stroke();
      ctx.restore();
     } else if (
      (i >= 4 && i <= 6)
      || (i >= (2*9)+3 && i <= (2*9)+4)
      || (i >= (2*17)+3 && i <= (2*17)+4)
      || (i >= (2*25)+3 && i <= (2*25)+4)
     ) {
      ctx.save();
      constraint.draw(ctx);
      ctx.strokeStyle = "#000";
      ctx.lineWidth = 2;
      ctx.stroke();
      ctx.restore();
     } else if (
      (i >= 6 && i <= 8)
      || (i >= (2*9)+5 && i <= (2*9)+6)
      || (i >= (2*17)+5 && i <= (2*17)+6)
      || (i >= (2*25)+5 && i <= (2*25)+6)
     ) {
      ctx.save();
      ctx.strokeStyle = "#000";
      ctx.lineWidth = 1.5;
      ctx.stroke();
      ctx.restore();
     } else {
      ctx.strokeStyle = "#000";
      ctx.stroke();
     }
    }
   }
  }