我正在尝试在Box2D中创建一个绕静态物体轨道运动的动态身体。
我有一个零重力的世界,和一个连接两个物体的DistanceJoint
。我已经从物体和关节中移除了所有摩擦和阻尼,并给动态物体施加了初始线性速度。结果是,物体开始绕着运动,但它的速度随时间减小 - 在没有摩擦的零重力环境中,这不是我所期望的。
我做错了什么吗?线性速度应该在每一步重新创建,还是可以委托给Box2D来完成这项工作?
以下是相关代码:
// positions of both bodies
Vector2 planetPosition = new Vector2(x1 / Physics.RATIO, y1 / Physics.RATIO);
Vector2 satellitePosition = new Vector2(x2 / Physics.RATIO, y2 / Physics.RATIO);
// creating static body
BodyDef planetBodyDef = new BodyDef();
planetBodyDef.type = BodyType.StaticBody;
planetBodyDef.position.set(planetPosition);
planetBodyDef.angularDamping = 0;
planetBodyDef.linearDamping = 0;
planetBody = _world.createBody(planetBodyDef);
CircleShape planetShapeDef = new CircleShape();
planetShapeDef.setRadius(40);
FixtureDef planetFixtureDef = new FixtureDef();
planetFixtureDef.shape = planetShapeDef;
planetFixtureDef.density = 0.7f;
planetFixtureDef.friction = 0;
planetBody.createFixture(planetFixtureDef);
// creating dynamic body
BodyDef satelliteBodyDef = new BodyDef();
satelliteBodyDef.type = BodyType.DynamicBody;
satelliteBodyDef.position.set(satellitePosition);
satelliteBodyDef.linearDamping = 0;
satelliteBodyDef.angularDamping = 0;
satelliteBody = _world.createBody(satelliteBodyDef);
CircleShape satelliteShapeDef = new CircleShape();
satelliteShapeDef.setRadius(10);
FixtureDef satelliteFixtureDef = new FixtureDef();
satelliteFixtureDef.shape = satelliteShapeDef;
satelliteFixtureDef.density = 0.7f;
satelliteFixtureDef.friction = 0;
satelliteBody.createFixture(satelliteFixtureDef);
// create DistanceJoint between bodies
DistanceJointDef jointDef = new DistanceJointDef();
jointDef.initialize(satelliteBody, planetBody, satellitePosition, planetPosition);
jointDef.collideConnected = false;
jointDef.dampingRatio = 0;
_world.createJoint(jointDef);
// set initial velocity
satelliteBody.setLinearVelocity(new Vector2(0, 30.0f)); // orthogonal to the joint