Creating custom collision shape #4534

luis605 · 2023-10-13T19:36:00Z

luis605
Oct 13, 2023

Hi everyone!

I passed here to ask you if you know how to create a custom bullet collision shape. I am trying to convert a raylib mesh into a bullet physics shape and I am not having that much luck with it. For some strange reason, the tree is falling through the floor, instead of colliding with it. I have tried to change the shape to a sphere and, in that case, the collision works perfectly, which means my issue is probably with my attempt of converting a mesh into a shape. As I don't want a sphere as my collider, only a custom shape, I came here to ask you for help.

here is my code for reference:

    InitWindow(800, 600, "Raylib + Bullet Physics Example");
    
    btDefaultCollisionConfiguration* collisionConfiguration = new btDefaultCollisionConfiguration();
    btCollisionDispatcher* dispatcher = new btCollisionDispatcher(collisionConfiguration);
    btBroadphaseInterface* overlappingPairCache = new btDbvtBroadphase();
    btSequentialImpulseConstraintSolver* solver = new btSequentialImpulseConstraintSolver();
    btDiscreteDynamicsWorld* dynamicsWorld = new btDiscreteDynamicsWorld(dispatcher, overlappingPairCache, solver, collisionConfiguration);
    dynamicsWorld->setGravity(btVector3(0, -9.81, 0)); 

    Model treeModel = LoadModel("assets/models/tree.obj");
    
    btTriangleMesh* treeTriMesh = new btTriangleMesh();
    
    for (int m = 0; m < treeModel.meshCount; m++) {
        Mesh mesh = treeModel.meshes[m];
        float* meshVertices = (float*)mesh.vertices;

        for (int v = 0; v < mesh.vertexCount; v += 9) { 
            Vector3 v1 = { meshVertices[v], meshVertices[v + 1], meshVertices[v + 2] };
            Vector3 v2 = { meshVertices[v + 3], meshVertices[v + 4], meshVertices[v + 5] };
            Vector3 v3 = { meshVertices[v + 6], meshVertices[v + 7], meshVertices[v + 8] };

            std::cout << v1.x << ", " << v1.y << ", " << v1.z << std::endl;
            std::cout << v2.x << ", " << v2.y << ", " << v2.z << std::endl;
            std::cout << v3.x << ", " << v3.y << ", " << v3.z << std::endl;
            std::cout << std::endl;

            treeTriMesh->addTriangle(
                btVector3(v1.x, v1.y, v1.z),
                btVector3(v2.x, v2.y, v2.z),
                btVector3(v3.x, v3.y, v3.z)
            );
        }
    }


    btBvhTriangleMeshShape* treeShape = new btBvhTriangleMeshShape(treeTriMesh, true);
    treeShape->buildOptimizedBvh();

    btTransform treeTransform;
    treeTransform.setIdentity();
    treeTransform.setOrigin(btVector3(0, 10, 0)); 

    btDefaultMotionState* treeMotionState = new btDefaultMotionState(treeTransform);
    btScalar treeMass = 1.0f;
    btVector3 treeInertia(0, 0, 0);
    treeShape->calculateLocalInertia(treeMass, treeInertia);
    btRigidBody::btRigidBodyConstructionInfo treeRigidBodyCI(treeMass, treeMotionState, treeShape, treeInertia);
    btRigidBody* treeRigidBody = new btRigidBody(treeRigidBodyCI);

    dynamicsWorld->addRigidBody(treeRigidBody);