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<head>
<title>Verlet Spiderweb</title>
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<body>
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<div id="header">
<h1><a href="../">verlet-js</a> / <em>Spiderweb</em></h1>
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<p>
<h4>Author</h4>
<a href="http://subprotocol.com/">Sub Protocol</a>
<h4>Summary</h4>
This web was spun using sinusoidal functions, distance tensioners, and pin constraints to hold it all up.
Initially the spider was really good at playing <i>Twister</i> by itself (too good), and not so much at crawling.
My solution to help the spider crawl was to create a quadrant off the spiders origin and axis. Each leg is designated a quadrant (2 legs per quadrant) that the spider steps into.
The spider can be pulled off the web.
<h4>Source Code</h4>
<a href="https://github.com/subprotocol/verlet-js/blob/master/examples/spiderweb.html">View on GitHub</a>
</p>
</div>
<canvas id="scratch" style="width: 800px; height: 500px;"></canvas>
<script type="text/javascript">
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));
// legs
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();
// particles
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);
// constraints
for (i=0;i<n-1;++i) {
// neighbor
composite.constraints.push(new DistanceConstraint(composite.particles[i], composite.particles[i+1], stiffness));
// span rings
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;
}
//+ Jonas Raoni Soares Silva
//@ http://jsfromhell.com/array/shuffle [v1.0]
function shuffle(o) { //v1.0
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;
var leftFoot = false;
var j;
for (j in spider.constraints) {
var k;
for (k=0;k<8;++k) {
if (
spider.constraints[j] instanceof DistanceConstraint
&& spider.constraints[j].a == spider.legs[k]
&& spider.constraints[j].b == spiderweb.particles[i])
{
leftFoot = true;
}
}
}
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 dimensions
var width = parseInt(canvas.style.width);
var height = parseInt(canvas.style.height);
// retina
var dpr = window.devicePixelRatio || 1;
canvas.width = width*dpr;
canvas.height = height*dpr;
canvas.getContext("2d").scale(dpr, dpr);
// simulation
var sim = new VerletJS(width, height, canvas);
// entities
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);
// draw legs
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();
}
}
}
}
spider.drawParticles = function(ctx, composite) {
}
// animation loop
var legIndex = 0;
var loop = function() {
if (Math.floor(Math.random()*4) == 0) {
sim.crawl(((legIndex++)*3)%8);
}
sim.frame(16);
sim.draw();
requestAnimFrame(loop);
};
loop();
};
</script>
<div id="footer">
Copyright 2013 Sub Protocol and other contributors.
<br/><a href="http://subprotocol.com/">http://subprotocol.com/</a>
</div>
</body>