Solution: Align Pivot To Another Object Without Affecting Geometry in MaxScript

This code can be used to Align a pivot of an object to another object or
some other arbitrary matrix without affecting the position of the original geometry.

Potential Usage: programmatically moving pivots before export so your model
will look right in your game engine.

Function ReAssignPivot
inputTransform  --New Transform Matrix To Be Pivot
&theObject      --The Object to Act on.
--Function Description:
--Gives the object a new pivot, defined by a transform matrix.
--Does so WITHOUT affecting the world position of the original geometry.
--
--**************************************************************
--   More Free Scripts: www.ProofOfProgress.BlogSpot.com     ***
--**************************************************************
--
=(
 --VLM = Visible Local Matrix.
 --The matrix/pivot you see when selecting object and "Local" axis is selected as viewable.
 VLM = theObject.Transform;
 IP_LocalRot = theObject.objectOffsetRot; --Rotation to be used later.
 IP_LOCAL = theObject.objectOffsetPos;  --Invisible Pivot Local coordinates
             --In relation to VLM matrix.
 IP_WORLD = IP_LOCAL * VLM; --World Coordinates of Invisible Pivot. [Local To World Transform]
 VLM_0 = inputTransform; --Reset Visible Local matrix coordinates.
 
 NEW_IP_LOCAL = IP_WORLD * inverse(VLM_0); --[World To local Transform]
 
 theObject.Transform = VLM_0;
 theObject.objectOffsetPos = NEW_IP_LOCAL;

 --Now Handle Rotation:
 --Since rotation of visible local matrix has been zeroed out,
 --You must add that loss to the invisible pivot rotation.
 
 RotationLoss = VLM.RotationPart - VLM_0.RotationPart;
 GeomWorldRot = RotationLoss + IP_LocalRot;
 theObject.objectOffsetRot = GeomWorldRot;
 
)--[FN:ReAssignPivot]

--Test Code;
--This test code will align SomeCircle's pivot to PivotObject's Pivot.
inputTransform = $PivotObject.Transform;
affectedObject = $SomeCircle;
ReAssignPivot inputTransform &OBJ;