View Full Version : Breaking objects and keeping UVs intact

01-10-2010, 03:00 AM
Hello guys,

Having a piece of a problem here... I have an object (a building) which is fully UV textured and unwrapped. Now I need to break it in pieces. This part is pretty easy, the problem is that as soon as I break something, the UV maps get all messed up!

I was expecting that if I made a seam in a polygon, this seam would also appear in the UVMap without messing up the rest of the points... but noooooo, the damn points jump all over the place in the UV space!

I already tried C4, CrackIt, MGBreakUpMD to no avail. I even tried to do it by hand, using knife... but not even that thing works without messing the UVs up here and there!

Having to redo all the UVMaps AGAIN is not something I am looking forward.. not to mention that now it will be much more difficult because of all the pieces. What I wanted was that a wall texture would remain in the same place in the respective polygons after broken.

If anyone know some technique for this, please advise!

Thank you!

CC Rider
01-11-2010, 11:04 AM
Are your building objects subpatched?

01-11-2010, 04:47 PM
No subpatches, just plain hard-modeling. But as soon as I try to cut the polygons, booom, points going everywhere in the UVMap!

01-11-2010, 08:41 PM
Can you upload a few images of the UV map?

01-14-2010, 03:19 AM

Here is a very simple model, which is supposed to be a small castle for a tiny 3D icon in a game. This castle is going to be destroyed. I wanted to break the model in pieces and maintain the main UV features so that the base texture would be the same and then paint some cracks/debris over it.

In image 2 is what happens to the UV maps just after two simple straight cuts... imagine what it becomes in the end after a ton of them in a whole castle!

PS: And what's up with all those extra points in the middle of the UV?

Anyway, I already managed to do this by painstakingly moving all the freaking points by hand and rearranging the UV map, which took hours!

Then I came up with a new problem: baking the surface into the UVMap! I just wanted to bake the GI solution into the UVMap in order to use it as a reference for texture painting and, at the same time, to use as simulated ambient occlusion over the texture... I got a baked texture with tons of random line-artifacts! Jesus Christ! Does anything work correctly in here? The other textures got even worse than this one!

01-14-2010, 06:46 AM
Well i'm not totally understanding your needs and limits, but:

-UV's- Some things you can try.
..I built a structure similar to yours and i had same issues in some cuts (meaning Uv's discontinous points messed up and floating points were created). But if i unweld first before i start cutting the problem would not persist.
..Exporting the object to OBJ might purge some UV issues (like the floating points). As for cutting, the first cut went ok, but second became jagged. And if i applyed Merge Points or Weld UV the problem would resurface in the first cut. I guess this has to do with discontinous points issues.
..Another way to solve the floating points (if the mesh isn't screwed) is to select all polygons in UV view, move them to the side, like 1 meter (FREE MOVE ON in the Viewport), and the floating points will be left behind, so just select them, apply Clear Map, and move the polygons back to place.

-Baking OC-
..What are the setting you are using? I think Offset from surface is what i normally used to correct that.
..Also, are your UV's clean?
..Have you tryed to triple your object at bake time?

Good luck.
A test file would be cool =)

01-17-2010, 08:58 AM
Hi again, probiner, thanks for the reply!

Well, I cannot unweld+weld because I already have some unwelded points that I want to remain that way, so if I unweld all and try to weld all again, I will get to reselect those joints I want unwelded and unweld again... Of course I could reselect them and make a pointset for easy selection, but sincerely, all that unweld/weld workflow is really cumbersome

As for the UVs, thanks for the suggestions. I haven't tripled the polygons and that helped a little. But the "Offset from surface" made no difference, and I tried several measurements, from 10um to 1 m!

Anyway, things are going... with much more tiresome work than expected!

01-17-2010, 09:41 AM
Sorry to know =\

Only issue i see that could bother you by unwelding and merging is point order, that gets changed. Because there is a 'simple' way to keep those points unwelded when you hit merge. Watch one minute of the video (http://www.youtube.com/watch?v=8eIiQboLUA4#t=3m30s&h=1). This way you might be able to unweld, make cuts, merge without losing the seams.

As for the baking process, i don't do it much. But not the first time someone gets bad results with baking camera, so some thread or someone might have a good straight answer for that.


01-17-2010, 12:10 PM
Lightwave is just peculiar with its UV technology sometimes. try this, make a 1m by 1m cube, with something like 10 segments on each side. make a Linear Atlas UV of it.
Now copy and paste that cube from layer 1 to layer 2, and check out the UV map. Everytime I do it I get one polygon that flips its lid and goes all weird.

Back in the day there was an ancient UVMapping plugin, I wonder if it still works in 9.6... must dig through the archive and check it out. I think it was called Truview?

- Will.

01-17-2010, 12:20 PM
As tough as it may be could you break the object up THEN reuvmap it? If you export out the original UV map with UVImaginator you could reload that image in as a background then 'rebuild' the UV by moving the UV points around into their old positions using the background image as a guide. Seems like a lotta work but I think it would actually work.
Or a variation thereof...

- Will.