RigidBody with imported obj in THREE.js and Ammo.js Collision

[Coder-345]

I have imported 3d obj and glb files in my THREE.js and Ammo.js project . For example lets take say i have a tiger obj and a lion obj or glb file.

I need to apply Rigidbody constraint to both of them so when they move towards each other they should collide.

I found this Rigidbody code in ammo.js example which applies Rigidbody collision to a plane or a block basically something in cube or Box dimension.

  var threeObject = new THREE.Mesh(new THREE.BoxGeometry(sx, sy, sz, 1, 1, 1), material);
  var shape = new Ammo.btBoxShape(new Ammo.btVector3(sx * 0.5, sy * 0.5, sz * 0.5));
  shape.setMargin(margin);
  createRigidBody(threeObject, shape, mass, pos, quat);

But in my case as I couldn't predict the shape , How can I achieve this ..

I saw this post that was similar to my problem . But I couldn't understand how to implement that. How can I use btBvhTriangleMeshShape with my imported obj or gltf . Link to that Post

How can I apply the Rigidbody function to my loaded obj model.

 var objLoader2 = new THREE.OBJLoader();
 objLoader2.load('../../objfiles/Object.obj', function(object) {
     scene.add(object);
                   
 });

Do someone have the code for that. Or if someone could help me solve this problem it would be of great help .

[jcguarinpenaranda]

I also have the same doubt. Any help would be very much appreciated.

[Fsmash]

https://pybullet.org/Bullet/phpBB3/viewtopic.php?t=437

Sorry, it isn't a ammo.js example and they don't have example code which is the most annoying part. But they do mention two options you can use. I would look for C++ code of Bullet that uses convex hull or compounds. I would go for convex hull but if your model has a concave spot in it that has to be detected then you will have to use compound.

[OliverXH]

It's not difficult to apply mesh collision shape to imported model, but it seems like two mesh collision shape can't collide with each other

https://github.com/kripken/ammo.js/issues/339

[dataexcess]

Hello,

you can do this using following code:

`

    static createPhysicsMeshFromGeometry(geometry) {

    const triangleMesh = new Ammo.btTriangleMesh();

    const vectA = new Ammo.btVector3(0, 0, 0);
    const vectB = new Ammo.btVector3(0, 0, 0);
    const vectC = new Ammo.btVector3(0, 0, 0);

    const verticesPos = geometry.getAttribute('position').array;
    const triangles = [];
    for (let i = 0; i < verticesPos.length; i += 3) {
        triangles.push({
                x: verticesPos[i],
                y: verticesPos[i + 1],
                z: verticesPos[i + 2]
        })
    }

    for (let i = 0; i < triangles.length - 3; i += 3) {
        vectA.setX(triangles[i].x);
        vectA.setY(triangles[i].y);
        vectA.setZ(triangles[i].z);

        vectB.setX(triangles[i + 1].x);
        vectB.setY(triangles[i + 1].y);
        vectB.setZ(triangles[i + 1].z);

        vectC.setX(triangles[i + 2].x);
        vectC.setY(triangles[i + 2].y);
        vectC.setZ(triangles[i + 2].z);

        triangleMesh.addTriangle(vectA, vectB, vectC, true);
    }

    let shape = new Ammo.btBvhTriangleMeshShape(triangleMesh, true);
    geometry.verticesNeedUpdate = true
    shape.setMargin(0.05);

    return shape;
}

//then later call it...

{

        this.objLoader = new OBJLoader();
        this.objLoader.load(mapModel, (root) => {

        let model = root.children[0]
        this.geometry = model.geometry

        let physicsBody = PhysicsManager.createPhysicsBodyFromGeometry(this.geometry)


        PhysicsManager.physicsWorld.addRigidBody(
            physicsBody
        )
    };

`