Make a bullet shape around model in libgdx

Question

How do I make a btBoxShape around a Model or ModelInstance in Libgdx? This is my code:

modelInstance.calculateBoundingBox(boundingBox);
collisionShape = new btBoxShape(boundingBox.getDimensions(tempVector3).scl(.5f));

This works and creates a box of the right size but it is offset from the model. I cant figure out how to make it around the model and not offset.

Answer 1

You have to use a btMotionState to synchronize model and bullet transforms. You use it like this (example taken from LibGDX wiki):

// Create your own implementation
public class MyMotionState extends btMotionState {
    Matrix4 transform;

    @Override
    public void getWorldTransform (Matrix4 worldTrans) {
        worldTrans.set(transform);
    }

    @Override
    public void setWorldTransform (Matrix4 worldTrans) {
        transform.set(worldTrans);
    }
}

// Then attach it to your body
btRigidBody body = ...;
ModelInstance instance = ...;
MyMotionState motionState = new MyMotionState();
motionState.transform = instance.transform;
body.setMotionState(motionState);

The wiki is a very good place to get information about how to use the wrapper. You should also check out Xoppa's blog on the subject as he goes into more in-depth solutions.

Answer 2

You are setting it to offset with scaling dimensions with 0.5f . Try not to scale it or just create new vector3 at {0,0,0} .

collisionShape = new btBoxShape(boundingBox.getDimensions(tempVector3));