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aresye
Post  Post subject: Geometry w/ Negative Scale Appearing Black: Workaround  |  Posted: Fri Mar 14, 2014 10:32 pm

Joined: Fri Feb 14, 2014 11:25 am
Posts: 10

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When I encountered this problem this past week, I discovered there were a few people struggling with this same issue, but while the simple fix is to simply freeze transformations to get rid of the negative scale, this approach caused problems with geometry affected by deformers like lattices, as the freezing of transforms essentially unlinked the deformers from the geometry.

My Problem:
I had a character with non-spherical eyes which complicated rigging. I could not simply create an aim constraint, as the rotation of the eye would cause it to pop in-out of the socket geometry.

My Solution:
The first eye was modeled as a perfect sphere and placed in the approx. location for the eye socket. A lattice deformer was applied to shape the eye to the socket. This lattice was parented to the head joint in addition to the eye geometry. Once an aim constraint was applied to the eye target, the lattice kept the shape of the eye despite the eye rotating.

Next Problem:
I needed my other eye, but I also needed the lattice as well, and it needed to keep the same shape and remain active despite duplicating it.

Next Solution:
First, I unparented the original eye and lattice from the head joint, and grouped them together (L_Eye, L_Eye_LAT, and ffd1base), renaming it L_Eye_GRP. Next I selected the entire group, and performed a "duplicate special," ensuring the box, "duplicate input graph," was selected. I renamed this new group R_Eye_GRP. In order to flip the lattice and eye geometry to the right side, I selected the group and typed, "-1" into Scale X. Eye and lattice both swapped to the other side perfectly, and rotating the eye showed that the lattice was still active on the new eye.

Final Problem:
While there are no issues in the viewport or other renderers, the duplicated right eye would show up as a black sphere in FurryBall. This can't do!

Final Solution:
The main issue causing the eye to appear black is in fact the negative scale attached to it, but the solution isn't just a simple, "freeze transforms," as this would disconnect the eye from the lattice, ruining the eye's fit to the eye socket, returning it to its original sphere shape.

To solve this, we need to turn off the lattice, freeze transforms on the eye, and then turn on the lattice again. How do we do this? Go to Window>>Relationship Editors>>Deformer Sets. On the left side, select the lattice you want to turn off. In my case, the duplicated lattice for the R_Eye was called "ffd1set1." On the right side, open your R_Eye_GRP, and select the R_Eye geometry itself. By clicking it off, you'll notice the eye resuming its original shape, no longer being affected by the lattice. Now we are free to select the R_Eye geometry in the main outliner, and freeze its transformations. Now that its scale has been properly reset, go back into your Deformer Sets editor, select your lattice on the left side again, and click your R_Eye geometry on the right side to turn it back on.

If all goes correctly, your eye should return to the shape created by the lattice, and when rotating the eye, the lattice ensures the shape stays consistent. Jump into FurryBall, and your eye should no longer be black.



Overall, not that hard of a process at all, but one that doesn't have much documentation on how to do it, as most renderers don't have a problem rendering geometry with a negative scale. Hope this helps some of you who have or are currently experiencing this issue unique to FurryBall, and I hope this helps provide a possible solution for you.

Here's the final result. No artifacts, no black geo, and both lattices working correctly:
Image
http://s9.postimg.org/p6crptg4t/eye_Rigging.gif


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Jan_Tomanek
Post  Post subject: Re: Geometry w/ Negative Scale Appearing Black: Workaround  |  Posted: Sat Mar 15, 2014 10:29 am
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Joined: Tue Oct 27, 2009 11:03 pm
Posts: 1607
Location: Prague - Czech republic

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Thanks to post it here.

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