/** 开始拖动刚体*/
private void startDragBody(b2Body b, float x, float y)
{
if (b == null || b.GetType() != b2Body.b2_dynamicBody)
{
return;
}
if (_mj != null)
{
_world.DestroyJoint(_mj);
}
b2MouseJointDef jointDef = new b2MouseJointDef();
jointDef.bodyA = _world.GetGroundBody();
jointDef.bodyB = b;
jointDef.target.Set(x, y);
jointDef.maxForce = 1e6f;
_mj = _world.CreateJoint(jointDef) as b2MouseJoint;
}
public virtual bool MouseDown(b2Vec2 p)
{
m_mouseWorld = p;
if (m_mouseJoint != null)
{
return(false);
}
// Make a small box.
b2AABB aabb = new b2AABB();
b2Vec2 d = new b2Vec2();
d.Set(0.001f, 0.001f);
aabb.LowerBound = p - d;
aabb.UpperBound = p + d;
// Query the world for overlapping shapes.
QueryCallback callback = new QueryCallback(p);
m_world.QueryAABB(callback, aabb);
if (callback.m_fixture != null)
{
b2Body body = callback.m_fixture.Body;
b2MouseJointDef md = new b2MouseJointDef();
md.BodyA = m_groundBody;
md.BodyB = body;
md.target = p;
md.maxForce = 1000.0f * body.Mass;
m_mouseJoint = (b2MouseJoint)m_world.CreateJoint(md);
body.SetAwake(true);
return(true);
}
return(false);
}
public Wheel(
b2World b2world,
double x,
double y,
double width,
double length,
bool revolving,
bool powered
)
{
this.revolving = revolving;
this.powered = powered;
this.Initialize = car =>
{
/*
* wheel object
*
* pars:
*
* car - car this wheel belongs to
* x - horizontal position in meters relative to car's center
* y - vertical position in meters relative to car's center
* width - width in meters
* length - length in meters
* revolving - does this wheel revolve when steering?
* powered - is this wheel powered?
*/
var position = new double[] { x, y };
//this.car=pars.car;
//this.revolving=pars.revolving;
//this.powered=pars.powered;
//initialize body
var def = new b2BodyDef();
def.type = b2Body.b2_dynamicBody;
def.position = car.body.GetWorldPoint(new b2Vec2(position[0], position[1]));
def.angle = car.body.GetAngle();
this.body = b2world.CreateBody(def);
//initialize shape
var fixdef = new b2FixtureDef();
fixdef.density = 1;
fixdef.isSensor = true; //wheel does not participate in collision calculations: resulting complications are unnecessary
var fixdef_shape = new b2PolygonShape();
fixdef.shape = fixdef_shape;
fixdef_shape.SetAsBox(width / 2, length / 2);
body.CreateFixture(fixdef);
var jointdef = new b2RevoluteJointDef();
//create joint to connect wheel to body
if (revolving)
{
jointdef.Initialize(car.body, body, body.GetWorldCenter());
jointdef.enableMotor = false; //we'll be controlling the wheel's angle manually
}
else
{
jointdef.Initialize(car.body, body, body.GetWorldCenter()
//, new b2Vec2(1, 0)
);
jointdef.enableLimit = true;
//jointdef.lowerTranslation = 0;
//jointdef.upperTranslation = 0;
}
b2world.CreateJoint(jointdef);
#region setAngle
this.setAngle =
(angle) =>
{
/*
* angle - wheel angle relative to car, in degrees
*/
body.SetAngle(car.body.GetAngle() + angle.DegreesToRadians());
};
#endregion
#region getLocalVelocity
Func <double[]> getLocalVelocity = delegate
{
/*returns get velocity vector relative to car
*/
var res = car.body.GetLocalVector(car.body.GetLinearVelocityFromLocalPoint(new b2Vec2(position[0], position[1])));
return(new double[] { res.x, res.y });
};
#endregion
#region getDirectionVector
Func <double[]> getDirectionVector = delegate
{
/*
* returns a world unit vector pointing in the direction this wheel is moving
*/
if (getLocalVelocity()[1] > 0)
{
return(vectors.rotate(new double[] { 0, 1 }, body.GetAngle()));
}
else
{
return(vectors.rotate(new double[] { 0, -1 }, body.GetAngle()));
}
};
#endregion
#region getKillVelocityVector
Func <double[]> getKillVelocityVector = delegate
{
/*
* substracts sideways velocity from this wheel's velocity vector and returns the remaining front-facing velocity vector
*/
var velocity = body.GetLinearVelocity();
var sideways_axis = getDirectionVector();
var dotprod = vectors.dot(new[] { velocity.x, velocity.y }, sideways_axis);
return(new double[] { sideways_axis[0] * dotprod, sideways_axis[1] * dotprod });
};
#endregion
#region killSidewaysVelocity
this.killSidewaysVelocity = delegate
{
/*
* removes all sideways velocity from this wheels velocity
*/
var kv = getKillVelocityVector();
body.SetLinearVelocity(new b2Vec2(kv[0], kv[1]));
};
#endregion
};
}
