Method computeFrictionVectors

src/systems/ContactSolverSystem.cpp:789–818

Compute the two unit orthogonal vectors "t1" and "t2" that span the tangential friction plane for a contact manifold. The two vectors have to be such that : t1 x t2 = contactNormal.

// Compute the two unit orthogonal vectors "t1" and "t2" that span the tangential friction plane
// for a contact manifold. The two vectors have to be such that : t1 x t2 = contactNormal.
void ContactSolverSystem::computeFrictionVectors(const Vector3& deltaVelocity, ContactManifoldSolver& contact) const {

    RP3D_PROFILE("ContactSolver::computeFrictionVectors()", mProfiler);

    assert(contact.normal.length() > decimal(0.0));

    // Compute the velocity difference vector in the tangential plane
    decimal deltaVDotNormal = deltaVelocity.dot(contact.normal);
    Vector3 normalVelocity = deltaVDotNormal * contact.normal;
    Vector3 tangentVelocity(deltaVelocity.x - normalVelocity.x, deltaVelocity.y - normalVelocity.y,
                            deltaVelocity.z - normalVelocity.z);

    // If the velocty difference in the tangential plane is not zero
    const decimal lengthTangentVelocity = tangentVelocity.length();
    if (lengthTangentVelocity > MACHINE_EPSILON) {

        // Compute the first friction vector in the direction of the tangent
        // velocity difference
        contact.frictionVector1 = tangentVelocity / lengthTangentVelocity;
    }
    else {

        // Get any orthogonal vector to the normal as the first friction vector
        contact.frictionVector1 = contact.normal.getOneUnitOrthogonalVector();
    }

    // The second friction vector is computed by the cross product of the first
    // friction vector and the contact normal
    contact.frictionVector2 = contact.normal.cross(contact.frictionVector1);
}