How do you stop OgreBullet Capsule from falling over?

Question

I've just started implementing bullet into my Ogre project. I follows the install instructions here: http://www.ogre3d.org/tikiwiki/OgreBullet+Tutorial+1

And the rest if the tutorial here: http://www.ogre3d.org/tikiwiki/OgreBullet+Tutorial+2

I got that to work fine however now I wanted to extend it to a handle a first person camera. I created a CapsuleShape and a Rigid Body (like the tutorial did for the boxes) however when I run the game the capsule falls over and rolls around on the floor, causing the camera swing wildly around.

I need a way to fix the capsule to always stay upright, but I have no idea how

Below is the code I'm using.

(part of) Header File

OgreBulletDynamics::DynamicsWorld *mWorld;   // OgreBullet World
OgreBulletCollisions::DebugDrawer *debugDrawer;
std::deque<OgreBulletDynamics::RigidBody *>         mBodies;
std::deque<OgreBulletCollisions::CollisionShape *>  mShapes;

OgreBulletCollisions::CollisionShape *character;
OgreBulletDynamics::RigidBody *characterBody;
Ogre::SceneNode *charNode;

Ogre::Camera* mCamera;
Ogre::SceneManager* mSceneMgr;
Ogre::RenderWindow* mWindow;

main file

bool MinimalOgre::go(void)
{
    ...

     mCamera = mSceneMgr->createCamera("PlayerCam");
     mCamera->setPosition(Vector3(0,0,0));
     mCamera->lookAt(Vector3(0,0,300));
     mCamera->setNearClipDistance(5);
     mCameraMan = new OgreBites::SdkCameraMan(mCamera);


    OgreBulletCollisions::CollisionShape *Shape;
    Shape = new OgreBulletCollisions::StaticPlaneCollisionShape(Vector3(0,1,0), 0); // (normal vector, distance)
    OgreBulletDynamics::RigidBody *defaultPlaneBody = new OgreBulletDynamics::RigidBody(
            "BasePlane",
            mWorld);
    defaultPlaneBody->setStaticShape(Shape, 0.1, 0.8); // (shape, restitution, friction)
    // push the created objects to the deques
    mShapes.push_back(Shape);
    mBodies.push_back(defaultPlaneBody);

    character = new OgreBulletCollisions::CapsuleCollisionShape(1.0f, 1.0f, Vector3(0, 1, 0));

    charNode = mSceneMgr->getRootSceneNode()->createChildSceneNode();
    charNode->attachObject(mCamera);
    charNode->setPosition(mCamera->getPosition());

    characterBody = new OgreBulletDynamics::RigidBody("character", mWorld);
    characterBody->setShape(   charNode,
                    character,
                    0.0f,         // dynamic body restitution
                    10.0f,         // dynamic body friction
                    10.0f,          // dynamic bodymass
                    Vector3(0,0,0),     
                    Quaternion(0, 0, 1, 0));


    mShapes.push_back(character);
    mBodies.push_back(characterBody);

    ...
}

Answer 1

You can lock the angular motion of the capsule in order to prevent it from tipping over. Ogre doesn't expose this functionality directly, but you should be able to access the underlying bullet rigid body to accomplish what you need:

characterBody->getBulletRigidBody()->setAngularFactor(btVector3(0.0f,1.0f,0.0f));

This would lock rotation on the xaxis and zaxis, preventing the capsule from tipping over, but allowing rotation around the yaxis, so that the character can still turn.

At some point you may want to looking into using a kinematic character controller, but that's an answer to a different question.