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View Full Version : Drawbacks of negative scale in matrix

Xeash
02-05-2010, 04:19 AM
Of course you guys can sent me like "Hey go learn matrix math and think yourself"
but that i want to know it is not theory but real production-proven answer or practice. Thats why i'll try to ask :p

Lets imagine u have 3d package with rigging capabilities( e.g. max,maya,xsi,blender,houdini - its doesnt matter i think) and rigged here rig part of one character (it could be leg rig, arm rig, left tail or right head rig and etc.). For keeping things clean and scalable you parent the whole rig part setup under high level transform. Later you decided to mirror rig part to other side. SO...whats you going to do with transforms in rig part which needs mirroring (e.g. fk controls or bones to be able to raise shoulder using one direction of rotation axis) ?
Why u want to do it or not using negative scale? Whats drawbacks/advantages of that method?

Earlier i saw houdini's autorigging tools(standard in package) and there was used negative scale on transforms for rig mirroring(o_O?). So also my question is which method to work with transforms(using neg scale or other method) the best? And why?


Thanks for your time
eek
02-05-2010, 05:48 AM
Its because mirroring about a single axis and not transforming about the axis perpendicular to it will change the 'handedness' of that system i.e one side will now not be in the same coordinate system as the other.


You want to respect the same reference coordinate system throughout the rig, and transform one side about the axis perpendicular to your mirrored direction.
PEN
02-05-2010, 11:28 AM
There are a number of reasons that you don't want right and left handed matrix values. First off if you are exporting to something like a game engine it will probably not respect it and flip it back over for you, that would mess with everything that you have done.

Another is have you ever tried aligning a right and left handed matrix, it isn't possible.

Objects inheriting that left handed matrix that are right handed could end up with issues down the road when you are linking or unlinking objects and it is stepping in and out of handedness.

Just don't do it.
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02-05-2010, 11:28 AM
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