Hi all.

I have been looking for info on unwrapping models that require multiple faces mapped to the same area - like with buildings.

For example, if you use the mirror modifier, blender overlays the UV's in the same location. I was wondering if there was a way to do that without using the mirror modifier.

I have been working on a model of a fairly large non-square structure that has 6 wedge shape vents on the top, and for my purposes they would be fine with the exact same texture. Now I can manually lay them on top of each other easily on the UV map, but when you create a Ambient Occlusion it comes out very dark because Blender is of course creating the AO in the same position for all 6 vents.

The same can be said for the walls.

I have been googling for few hours now but can't seam to find anything useful, so can someone point me to some relevant information or a tutorial.

Thanks for any input.

Reliquia....

Sorry, I can't help you, but thanks for asking this question because it is an issue I've run across so many times while trying to make a model as efficient as possible. stacking the UVs on top of each other on the same texture messes with some lightmappers (GG the last time I tried it, several betas ago, and definitely UE4) as well as well as baking AO like you said, in my experience. If I'm missing something, I hope someone can "enlighten" us (pun intended). My only solution so far has been to make larger textures, using the same texture multiple times, thus making it much less efficient.


EDIT: I have tried tiling the texture map (I use Blender) but it seems to achieve the same results as stacking them on top of one another.

@Jerry Tremble, lol that might be a good google search term - didn't think of 'stacking', so will go off and try some more googling!

Thanks for the input. I am glad that someone else has wondered about this as I was kinda thinking I was just being a total noob!

When you use the mirror modifier the UV for the two halves are stacked (and mirrored) in the same location. So somehow blender knows that they are stacked and only renders the AO once. So I was hoping there is a way to tell blender that you want, like 3 or 4 faces mapped (stacked) to the same area on the UV, and only render the AO once instead of 3 or 4 times. This of course gives the ability to have more detail on the model.

I have tried mapping them to same location manually, which is not that difficult (can be time consuming though lol) and seams to create no problems in Game Guru except for light-mapping as you mentioned, however I have to use something like Shader Map to create the AO, but Blender gives a far better AO in my experience.

Now as you can see I have high-jacked your term 'stacked' which for the life of me I did not think of for my description, so I will go for another google hunt now.

Reliquia....

The reason mirror modifier treats the two UV areas as the same is be cause they are the same, not because they're stacked. Applying the mirror modifier assigns the two areas to the sane UV layer. I'm not sure if there is a way to assign two faces to a single UV manually, but if you find out ud live to know.

I have never used the mirror modifier for uv mapping, I have always mapped them manually myself, lol. It is indeed time consuming! Some models made by others don't seem to have issues with GG's lightmapper but mine always seem to. In UE4, though, at least the one's I've tried, always generate an "overlapping UV" error, and strange shadows occur.

You could try offsetting the UV elements. I tested this on 2 boxes, one with all six sides occupying the same UV space, and one with all the sides offset from each other, but I found that both lightmapped just fine. If you're getting a lightmapping error, then it's worth a try. I've attached a couple of images to show what I mean.

Thanks, Gtox! It's been a while since I tried it, but I've tried both methods before; Your first image is what I meany by stacking the UVs and the second is what I meant by "tiling" above. I really didn't know how to explain it. I was pretty sure I had the same issues but I will trust your advice and try it again at some point, when I have time to get back into modeling. You are by far much more knowledgeable and talented than I!

You could always try unique UV's slightly more complex and involved but not having any problems with using the new method.

@Jerry Tremble - since I couldn't recreate the lightmapping error and therefore don't know if offsetting the UVs works, you shouldn't trust my advice

I some times think it's the lightmapper it self

The main problems I find with light-mapping is that while the lighting can be really nice the end result is ruined, because sometimes the models smoothing is messed up, and any continuous rotational animations are broken.

Till now I tell myself I am doing something wrong with my models - but since I don't consider myself an expert in this area by any means, I really don't know what causes it.

Reliquia....

With animated models, i make them dynamic, and if i don't want them to move when walked into or "gravity" takes them, immobile is set to 1. That usually fixes most light mapping issue on animated models for me.