CODEWITHSUNDEEP
c#bulletphysics
livin_amuk
livin_amuk

Reputation: 1353

BulletPhysics - Door object spins uncontrollably when placed on ground

I am trying to simulate a door in BulletPhysics using a HingeConstraint. The following code works as intended, in that the cube pivots on its corner around the Y-axis, effectively swinging open like a door, but as soon as I place the object on the ground it begins flying around uncontrollably.

RigidBody body = physics.LocalCreateRigidBody(mass, Matrix4.CreateTranslation(new Vector3(0, 0.5f, 0)), new BoxShape(1, 1, 1));
body.UserObject = "Door";

Vector3 pivotInA = new Vector3(1, 1, 1);
Vector3 axisInA = new Vector3(0, 1, 0);
var hinge = new HingeConstraint(body, pivotInA, axisInA);

const float targetVelocity = 1.0f;
const float maxMotorImpulse = 1.0f;
hinge.EnableAngularMotor(true, targetVelocity, maxMotorImpulse);
physics.World.AddConstraint(hinge);

Disabling collisions between the door and ground would solve the problem but I am struggling to achieve this also. The documentation says you can set a collision type and mask for a body but only the World.AddRigidBody() constructor appears to take such parameters and as far as I can tell my door is added to the world as a Hinge and the ground is added automagically when calling LocalCreateRigidBody(), shown below.

CollisionShape groundShape = new BoxShape(10, 1, 10);
CollisionObject ground = LocalCreateRigidBody(0, Matrix4.CreateTranslation(0, -1, 0), groundShape);
ground.UserObject = "Ground";

How can I stop the door spinning out when it sits atop the ground?

Upvotes: 0

Views: 130

Answers (1)

Andres Traks
Andres Traks

Reputation: 171

You can write your own version of LocalCreateRigidBody that sets up the collision mask. LocalCreateRigidBody is a helper function in the BulletSharp demos and not a built-in function in Bullet.

Here is one way to set up the collision filter:

const CollisionFilterGroups groundGroup = (CollisionFilterGroups)0x40000000;

var groundMask = CollisionFilterGroups.AllFilter ^ CollisionFilterGroups.StaticFilter;
World.AddRigidBody(ground, groundGroup, groundMask);

var doorMask = CollisionFilterGroups.AllFilter ^ groundGroup;
World.AddRigidBody(door, CollisionFilterGroups.DefaultFilter, doorMask);

Another way to solve this is to make the door shorter so it's not close enough to the ground to generate collisions. Then render a larger graphics object in place of the smaller physics object. If you are using the BulletSharp demo framework, then you will have to modify the framework to support this.

Upvotes: 1

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