使用 Box2D 做一个 JansenWalker 机器人

在 Box2DFlash 的官网的首页有一个小 Demo，这个 Demo 中有11个例子，可以通过左右方向键查看不同的例子，里面的每个例子都非常有趣，但最让我感兴趣的，是其中一个叫 JansenWalker 的，里面是一个往右移动的机器人，有6只脚，交替着地往右边行走，如下图：

package org.easily.test.box2d
{
import Box2D.Common.Math.b2Mat22;
import Box2D.Common.Math.b2Math;
import Box2D.Common.Math.b2Vec2;
import Box2D.Dynamics.b2Body;
import Box2D.Dynamics.b2FilterData;
import Box2D.Dynamics.b2World;

import org.easily.box2d.b2Utils;

/**
* jansenWalker by box2d
* @author Easily
*/
public class JansenWalker
{
private var world:b2World;
private var center:b2Body;
private var bodies:Array = [];

public function JansenWalker(world_:b2World)
{
world = world_;
createWalker();
}

public function setPosition(pos:b2Vec2):void
{
pos = pos.Copy();
pos.x /= b2Utils.worldScale;
pos.y /= b2Utils.worldScale;

var offset:b2Vec2 = center.GetPosition().Copy();
offset.Subtract(pos);

center.SetPosition(pos);
for each (var body:b2Body in bodies)
{
var old:b2Vec2 = body.GetPosition().Copy();
old.Subtract(offset);
body.SetPosition(old);
}
}

private function createWalker():void
{
var type:int = b2Body.b2_dynamicBody;
var density:Number = 2;
var friction:Number = 0.5;
var resititution:Number = 0.3;

var radius:Number = 28;
var size:b2Vec2 = new b2Vec2(45, radius / 2);

var legNum:Number = 4;

var legW:Number = 50;
var legH:Number = 75;
var legLen1:Number = 55;
var legLen2:Number = 55;

var jointLen1:Number = 88;
var jointLen2:Number = 85;

var bodyIndex:int = -1;
var legIndex:int = -2;

//motor
var rect:b2Body = b2Utils.createRect(world, type, new b2Vec2, size, density, friction, resititution, bodyIndex);
var circle:b2Body = b2Utils.createCircle(world, type, new b2Vec2, radius, density, friction, resititution, bodyIndex);
b2Utils.revoluteJoint(world, rect, circle, new b2Vec2, new b2Vec2, true, 3, 1000);
center = circle;
bodies.push(rect);

//legs
var average:Number = 2 * Math.PI / legNum;
var anchor:b2Vec2, first:b2Vec2 = new b2Vec2(radius * 2 / 3, 0);
var m:b2Mat22 = new b2Mat22();

var leftm:b2Mat22 = new b2Mat22();
var rightm:b2Mat22 = new b2Mat22();
leftm.Set(Math.PI);

for (var i:int = 0; i < legNum; i++)
{
m.Set(i * average);
anchor = b2Math.MulMV(m, first);
createLeg(false, leftm);
createLeg(true, rightm);
}

function createLeg(right:Boolean, m:b2Mat22):void
{
var v1:b2Vec2 = new b2Vec2;
var v2:b2Vec2 = new b2Vec2(0,-legW);
var v3:b2Vec2 = new b2Vec2(legW,0);

var v4:b2Vec2 = new b2Vec2;
var v5:b2Vec2 = new b2Vec2(legW,0);
var v6:b2Vec2 = new b2Vec2(0,legH);

//upper leg
var vertices1:Array = right ? [v1, v2, v3] : [v1, b2Math.MulMV(m, v3), v2];
var triangle1:b2Body = b2Utils.createPolygon(world, type, new b2Vec2, vertices1, density, friction, resititution, legIndex);
bodies.push(triangle1);

//lower leg
var vertices2:Array = right ? [v4, v5, v6] : [v4, v6, b2Math.MulMV(m, v5)];
var triangle2:b2Body = b2Utils.createPolygon(world, type, new b2Vec2, vertices2, density, friction, resititution, legIndex);
bodies.push(triangle2);

//connect two legs
b2Utils.distanceJoint(world, triangle1, triangle2, new b2Vec2, new b2Vec2, legLen1);
b2Utils.distanceJoint(world, triangle1, triangle2, b2Math.MulMV(m, new b2Vec2(legW, 0)), b2Math.MulMV(m, new b2Vec2(legW, 0)), legLen2);

//bind upper leg
b2Utils.revoluteJoint(world, rect, triangle1, b2Math.MulMV(m, new b2Vec2(size.x*3/2, 0)), new b2Vec2);

//join motor
b2Utils.distanceJoint(world, circle, triangle1, anchor, new b2Vec2(0, -legW), jointLen1);
b2Utils.distanceJoint(world, circle, triangle2, anchor, new b2Vec2, jointLen2);
}
}
}
}

JansenWalker
有好的方法，或者有意思的代码，请告诉我~