Quaternion Quaternion::RotationBetween(Vector3 aStart, Vector3 aEnd)
{
glm::vec3 start = glm::normalize(aStart.Raw());
glm::vec3 end = glm::normalize(aEnd.Raw());
float cosTheta = glm::dot(start, end);
glm::vec3 rotationAxis;
if (cosTheta < -1 + 0.001f)
{
rotationAxis = glm::cross(Vector3::Forward(), start);
if (glm::length2(rotationAxis) < 0.01f)
{
rotationAxis = glm::cross(Vector3::Right(), start);
}
rotationAxis = glm::normalize(rotationAxis);
return glm::angleAxis(180.0f, rotationAxis);
}
rotationAxis = glm::cross(start, end);
float s = glm::sqrt( (1 + cosTheta) * 2.0f);
float invs = 1 / s;
return glm::quat(s * 0.5f, rotationAxis.x * invs, rotationAxis.y * invs, rotationAxis.z * invs);
}
Quaternion Quaternion::LookRotation(const Vector3 & aLookDirection, const Vector3 & aDesiredUp)
{
glm::quat quat1 = RotationBetween(Vector3::Forward(), aLookDirection).Raw();
glm::vec3 desiredUp = aDesiredUp.Raw();
glm::vec3 right = glm::cross(aLookDirection, desiredUp);
desiredUp = glm::cross(right, aLookDirection);
glm::vec3 newUp = quat1 * Vector3::Up().Raw();
glm::quat quat2 = RotationBetween(newUp, desiredUp);
return quat2 * quat1;
}