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Archive Notice: This thread is old and no longer active. It is here for reference purposes. This thread was created on an older version of the flipcode forums, before the site closed in 2005. Please keep that in mind as you view this thread, as many of the topics and opinions may be outdated.
 
p3pp8

April 02, 2005, 10:15 AM

Hello, i need a help to solve a math problem,
i got 2 points in space(say pivots), i need to get a matrix to orientate some point around by the line(axis) constructed from these 2 pivots(rotation around that line is not needed), what i'd like to obtain is a simple ik system for falling human bodies, something like the game hitman; read the text below excerpted from an old article by By Thomas Jakobsen in 2003:





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Actually, in Hitman corpses arenít composed of rigid bodies modeled by tetrahedrons. They are simpler yet, as they consist of particles connected by stick constraints in effect forming stick figures.


**** The position and orientation for each limb (a vector and a matrix) are then derived for rendering purposes from the particle positions using various cross products and vector normalizations ****


In other words, seen isolated each limb is not a rigid body with the usual 6 degrees of freedom. This means that physically the rotation around the length axis of a limb is not simulated. Instead, the skeletal animation system used to setup the polygonal mesh of the character is forced to orientate the leg, for instance, such that the knee appears to bend naturally. Since rotation of legs and arms around the length axis does not comprise the essential motion of a falling human body, this works out okay and actually optimizes speed by a great deal.
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i tried to make something similar but the rotation matrix derived from pivots rotates points about a wrong axis, consider that i got a skeletal deformation system to animate my meshes and i concatenate the inverse of original frame matrix by derived one, just to put back on local space points affected by the derived matrix.......... any idea?????? thanx in advance and sorry about my horrible english ;)!!!

 
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