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Gugis

Box2dweb top-down friction

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Hello.

I'm working on top-down 8 ball pool game. Box2D world has 0 gravity and when I use ApplyImpulse on ball it won't slow down and never stops. My question is how to apply friction for top down game?

You can test it here: http://impressive.lt/test/box2d/8ball.html

Source code:

<html>   <head>      <title>8ball</title>   </head>   <body onload="init();">      <canvas id="canvas" width="600" height="400" style="background-color:#333333;" ></canvas>   </body>   <script type="text/javascript" src="Box2dWeb-2.1.a.3.min.js"></script>   <script type="text/javascript">          function init() {         var   b2Vec2 = Box2D.Common.Math.b2Vec2            ,  b2AABB = Box2D.Collision.b2AABB         	,	b2BodyDef = Box2D.Dynamics.b2BodyDef         	,	b2Body = Box2D.Dynamics.b2Body         	,	b2FixtureDef = Box2D.Dynamics.b2FixtureDef         	,	b2Fixture = Box2D.Dynamics.b2Fixture         	,	b2World = Box2D.Dynamics.b2World         	,	b2MassData = Box2D.Collision.Shapes.b2MassData         	,	b2PolygonShape = Box2D.Collision.Shapes.b2PolygonShape         	,	b2CircleShape = Box2D.Collision.Shapes.b2CircleShape         	,	b2DebugDraw = Box2D.Dynamics.b2DebugDraw            ,  b2MouseJointDef =  Box2D.Dynamics.Joints.b2MouseJointDef            ;                  var world = new b2World(               new b2Vec2(0, 0)    //gravity            ,  true                 //allow sleep         );				function borders(){			 var borderFix = new b2FixtureDef;			 borderFix.density = 1.0;			 borderFix.friction = 0.5;			 borderFix.restitution = 0.2;			 borderFix.shape = new b2PolygonShape;			 borderFix.shape.SetAsBox(20, 2);			 var borderBody = new b2BodyDef;			 borderBody.type = b2Body.b2_staticBody;			 borderBody.position.Set(10, 400 / 30 + 1.8);			 world.CreateBody(borderBody).CreateFixture(borderFix);			 			 borderBody.position.Set(10, -1.8);			 world.CreateBody(borderBody).CreateFixture(borderFix);			 borderFix.shape.SetAsBox(2, 14);			 borderBody.position.Set(-1.8, 13);			 world.CreateBody(borderBody).CreateFixture(borderFix);			 borderBody.position.Set(21.8, 13);			 world.CreateBody(borderBody).CreateFixture(borderFix);		}				function balls(){			var cue, b1, b2, b3, b4, b5, b6, b7, b8, b9, b10, b11, b12, b13, b14, b15;			var ballFix = new b2FixtureDef;			ballFix.density = 1.0;			ballFix.friction = 0.5;			ballFix.restitution = 0.2;			var ballBody = new b2BodyDef;			ballBody.type = b2Body.b2_dynamicBody;			ballFix.shape = new b2CircleShape(0.4);			ballBody.position.x = Math.random() * 10;			ballBody.position.y = Math.random() * 10;			var ball = world.CreateBody(ballBody).CreateFixture(ballFix);			ball.GetBody().ApplyImpulse(new b2Vec2(1,0), new b2Vec2(0,0));		}		         var debugDraw = new b2DebugDraw();			debugDraw.SetSprite(document.getElementById("canvas").getContext("2d"));			debugDraw.SetDrawScale(30.0);			debugDraw.SetFillAlpha(0.5);			debugDraw.SetLineThickness(1.0);			debugDraw.SetFlags(b2DebugDraw.e_shapeBit | b2DebugDraw.e_jointBit);			world.SetDebugDraw(debugDraw);			window.setInterval(update, 1000 / 60);                  function update() {            world.Step(1 / 60, 10, 10);            world.DrawDebugData();            world.ClearForces();         };		 		borders();		balls();               };      </script>      </html>

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Set linear damping in your pool balls bodyDef.

 

Change to this 

var ballBody = new b2BodyDef;ballBody.type = b2Body.b2_dynamicBody;ballBody.linearDamping = 0.3;

Also if you want you can also set angularDamping to make the balls stop spinning.

Thanks, it looks much better now /m\

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