Applying force in object's local space, rotation

[Kukanani]

Hi all, I'm a n00b here (although not with C++).

I have a simple question. How can I apply force on a body relative to the direction the body's pointing? I tried doing this with rotate(), like so:

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        btVector3 force = btVector3(moveX, moveY, moveZ);
        force = force.rotate(btVector3(0,1,0), body->getOrientation().getY());
        body->applyForce(force, btVector3(0,0,0));

But my object moves at all kinds of odd angles. What am I doing wrong here?

thanks,
Kukanani

[Kukanani]

I have partially fixed the problem with this code:

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        btVector3 force = btVector3(mDirection.x, mDirection.y, mDirection.z);
        force = force.rotate(btVector3(0,1,0), -body->getOrientation().getAngle());

        std::cout << force.getX() << ", " << force.getY() << ", " << force.getZ() << ".\n";

        body->applyForce(force, btVector3(0, 50, 0));
        body->setAngularVelocity(btVector3(0, mRotation.y, 0));

But, above angles of about 120 degrees and -50 degrees, my motion is perpendicular to how it should be. I tried using the modulus (%) operator with pi, but I can't use it on a btScalar.

Kukanani

[Xuhai.Tang]

I have partially fixed the problem with this code:

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        btVector3 force = btVector3(mDirection.x, mDirection.y, mDirection.z);
        force = force.rotate(btVector3(0,1,0), -body->getOrientation().getAngle());

        std::cout << force.getX() << ", " << force.getY() << ", " << force.getZ() << ".\n";

        body->applyForce(force, btVector3(0, 50, 0));
        body->setAngularVelocity(btVector3(0, mRotation.y, 0));

But, above angles of about 120 degrees and -50 degrees, my motion is perpendicular to how it should be. I tried using the modulus (%) operator with pi, but I can't use it on a btScalar.

Kukanani

body->applyForce(force, btVector3(0,0,0));

why are the position of force always (0,0,0)?

[Flix]

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body->getWorldTransform()->getBasis()->getColumn(2);

gives the local Z direction of the body in world coordinates.
P.S. In some cases it can be useful to retrieve the body world transform from the body motion state.