View Full Version : Bump Maps in Xsi ... WTF is goin' on ?

07 July 2002, 02:36 PM
Ok so I've imported this OBJ mesh into XSI ( Including UVs ) and when I apply a Bump map I get really really strange results: I get positive elevation on some polygons and negative elevation on others ...from the same bump values ! It looks way f***ed up !
Am I doing something wrong or is this a known issue ? Can it be corrected ?

My Fault
07 July 2002, 06:10 PM
Have you checked the normals on the funky polygons?

07 July 2002, 06:58 PM
the normals are fine. I think it's something to do with the UVs...

07 July 2002, 01:42 PM
It's a bug and as fas as I know you can't correct it. Sometimes it happens, sometime it doesn't. Sorry for bringing the bad news, hope this is fixed in next release.

Salutations - Cheers
Bernard Lebel

07 July 2002, 06:35 PM
Thanks for the info Atyss. No wonder I couldn't get rid of it...
Nice one Softimage ! :thumbsdow

07 July 2002, 12:47 AM
yes you can fix it.

i've notices from my own experience and seeing other ppl having this that it has to do with geometry and how you UV edit it.

in my case the problem only appears at times in the areas of merging edge. by merging edge i mean the edge that devides a sphere in half for example. i always uvedit a half and then duplicate, merge, merge texture clusters into 1 and delete the other one so i have 1 nice uv cluster. so it happened to me twice that i saw bump stuff happening on polys that are connected to that "merging edge," i didn't know what to do but then i desided to delete that "merging edge" and problem disappeared. and if you want to add it back then do so after and it will be ok.

with other ppl's cases, i corrected them by deleting the looping edge inbetween those scred polys and it worked. after you can just create the edge back and tweak to right place. but strange thing is that in few of those cases ppl had this not in "merging edge" location but somewhere off. :shrug: maybe it's the way they model their stuff... :shrug:

anyway it's not a big bug and not a big deal to me. now i can corrected in like 2sec so it doesn't bother me plus it happens like every 10th (or more) object i texture.

just remember not to use bevel or duplicationi of points/edges/polys on meshes when you have them already uvedited, creating/deleting edges is the best way to fix this quickly. oh and also don't delete/recreate polys too. k in summery just use edge create/delete :)

yay softimage :thumbsup:

07 July 2002, 10:02 AM
Well, see, my objects are already skinned ( enveloped ? ), including clusters shapes, push operators and such, so really deleting and then readding edges doesn't sound like such a good idea. But you're absolutely right, actually having to rebuild your mesh to fit XSI's peculiar way of computing bump maps really is no big deal. they should leave it as it is, who uses bump anyways ?

08 August 2002, 10:26 AM
I had a similar problem. Only in my case the polygons weren't on a joining edge. It wasn't even a complete polygon, just half (unless I'm remembering in-correctly).

08 August 2002, 06:24 AM
that was informative. . . but doesnt sddress a similar issue with bump mapping i somtimes have.
it happens usually when im creating a new shader using the "volume FX" node. ill apply a bump map and it either wont work at all, or will shade my model as if it was a 'Constant' shader. -- completely flat--
another thing i might add is that this usually occurs when using one of Mental Rays own procedural texture nodes on bump map...
such as, [cellular---->BUMP + vein---->VOLUMEFX + CookTorrance] = skin ..... but instead of skin ,like i said , sometimes i get constant... whats going on here?

08 August 2002, 08:41 AM
have you tried to scale -1 your uv's ?

for sean_G: why do you use a volumefx node to do skin?

08 August 2002, 10:11 PM
for SSS... and a nice transluscent subsurface veining.

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