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# Static collisions, quaternions

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Hey all (again), I''m trying to bounce an object off a plane. I''ve taken care of the collision detection itself already, and the object can be treated as a sphere. I''ve also already calculated the normal of the plane (because it''s actually the inside of a tube, but that''s immaterial). I thought I''d figured out how to perform the collision response: Calculate the component of the object''s current velocity along the normal (impact = velocity dot -planenormal) Apply that component to the object''s velocity (velocity += planenormal * impact) Now I can''t tell if that''s ok or not.. because the second problem is that the object I''m working with has a position and a direction - stored as a quaternion. When moving the object, I rotate the vector (0,0,1) by that quaternion, multiply by the speed and add to the position; but how do I turn a velocity back into a quaternion? I''ve already extracted the speed (just the length of the new velocity vector) and normalised it; how do I build my new direction quaternion given a vector? I should be able to rotate the vector (0,0,1) by the quaternion and end up with the velocity-vector that I started with... Superpig - saving pigs from untimely fates, and when he''s not doing that, runs The Binary Refinery.

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Would I be right in thinking that it''s an axis-angle rotation between newVelocity and a vector f=(0,0,1), where the axis is (newVelocity X f) and the angle is acos(newVelocity • f)?

Superpig
- saving pigs from untimely fates, and when he''s not doing that, runs The Binary Refinery.

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