box2dweb：牆壁不反彈慢物體

我使用box2dweb作爲我的遊戲。我圍繞一個圓圈放置了四個盒子，並給這個圓圈一個初始速度。我預計這個圓會從牆上彈開，但圓形在碰撞後會與牆平行。只有當一個圓圈移動緩慢時纔會發生。一個圓圈最後總是停在牆上。我怎樣才能讓一個圈子的行爲正確？下面的腳本顯示了這個問題。box2dweb：牆壁不反彈慢物體

<!DOCTYPE HTML> 
<html lang="ja-JP"> 
<head> 
    <meta charset="UTF-8"> 
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script> 
    <script type="text/javascript" src="http://jsdo.it/Kon/box2dweb/js"></script> 
    <script type="text/javascript"> 

var Ball_Speed = 2.0; 

var b2Vec2 = Box2D.Common.Math.b2Vec2; 
var b2Body = Box2D.Dynamics.b2Body; 
var b2World = Box2D.Dynamics.b2World; 
var b2CircleShape = Box2D.Collision.Shapes.b2CircleShape; 
var b2DebugDraw = Box2D.Dynamics.b2DebugDraw; 

$(function(){  
    "use strict"; 
    var canvas = $("#canvas"); 
    canvas.css("width", 500); 
    canvas.css("height", 500); 
    canvas.get(0).width = 500; 
    canvas.get(0).height = 500; 

    var world = new b2World(new b2Vec2(0, 0), true); 

    var debugDraw = new b2DebugDraw(); 
    debugDraw.SetSprite(canvas.get(0).getContext("2d")); 
    debugDraw.SetDrawScale(100); 
    debugDraw.SetFillAlpha(0.9); 
    debugDraw.SetLineThickness(1.0); 
    debugDraw.SetFlags(b2DebugDraw.e_shapeBit | b2DebugDraw.e_jointBit); 
    world.SetDebugDraw(debugDraw); 

    var fixDef = new Box2D.Dynamics.b2FixtureDef; 
    fixDef.restitution = 1; 

    var bodyDef = new Box2D.Dynamics.b2BodyDef; 
    bodyDef.linearDamping = 0.2; 

    // Create Wall ////////////////////////////////////////////////////////////////// 
    function createWall(x, y, w, h){ 
     bodyDef.type = b2Body.b2_staticBody; 
     bodyDef.position.x = x + w/2; 
     bodyDef.position.y = y + h/2; 
     fixDef.shape = new Box2D.Collision.Shapes.b2PolygonShape; 
     fixDef.shape.SetAsBox(w/2, h/2); 
     world.CreateBody(bodyDef).CreateFixture(fixDef); 
    }  
    createWall(0, 0, 2, 0.1); 
    createWall(0, 0, 0.1, 2); 
    createWall(2, 0, 0.1, 2); 
    createWall(0, 2, 2, 0.1); 

    // Create Ball 
    fixDef.shape = new b2CircleShape(0.2); 
    bodyDef.type = b2Body.b2_dynamicBody; 
    bodyDef.position = new b2Vec2(1.5, 1.0); 
    bodyDef.linearVelocity = new b2Vec2(Ball_Speed, Ball_Speed); 
    world.CreateBody(bodyDef).CreateFixture(fixDef); 

    (function loop(){ 
     world.Step(1/60, 10, 10); 
     world.DrawDebugData(); 
     world.ClearForces(); 
     setTimeout(loop, 15); 
    })(); 
});  

    </script> 
</head> 
<body> 
    <canvas id="canvas"></canvas> 
</body> 
</html>

來源

2012-09-07 Kon