Texturing / UVs - Sharing faces between parts / shared UVs

[Shadowmage]

Hi all,

I've hit a bit of a quandry in my modeling/texturing.

I have several modular parts based on a common theme/form factor (at least 4 parts to start, probably several more when finished). Most of these parts have a few faces duplicated in each, namely the top and bottom ends (e.g. these faces are identical across all parts). Currently I am using a 1024x texture for each part, but upwards of 1/4 of each of those textures is used by these shared faces (even when the faces have been split vertically and mirrored, so I'm only UV'ng half of the face).

I suppose my question(s) are thus:

Is it acceptable practice to 'atlas' multiple parts onto the same texture? -- this would allow me to use one texture area for all of those faces, expand the UV area for all faces, but would result in a 2048x texture for the set of parts (as a bonus, it would allow for very consistent scaling across all faces).

Would it be better to have a separate texture -just- for the shared faces for the part set, and leaving the other textures separate? -- would still free up UV space for the other faces, but would result in an extra material bind/draw call for those pieces.

Basically, I'm looking to decrease wasted UV space on duplicate faces while also ensuring that the texture is consistent across all of those identical faces. Thoughts?

Edit: For reference, a WIP render of some of the parts (RCS quads and engines are fully modeled/textured models that will be included in the finished parts):

Edited April 21, 2015 by Shadowmage

[CaptainKipard]

Yes that's fine. Generally speaking if your geometry is symmetrical you can use the same UV space, and even bake consistent ambient occlusion to it. I would recommend against reusing UVs for meshes that are slightly different.

[Shadowmage]

Thanks for the response.

The duplicate faces I'm looking to share UVs on are.. well.. exactly identical All cloned from the same initial mesh, starting with the same UVs, AO would/should/does bake identically.

I guess I'll play around a bit and see what works best from a workflow standpoint.

I know that atlased textures work great if everything is finalized; as soon as you try to change stuff though, it can go sideways pretty fast. Would also make it more difficult if adding additional parts at a later date; would be forced to re-map those shared faces, or use the previous texture / material.

I really like the idea of using a separate texture just for all of the shared faces and props, but I'm unsure of the kind of performance hit an additional material/draw call would have. Sounds like I may end up going this route anyhow (if I make any change at all). Probably also the easiest from a workflow standpoint; no need to do crazy mutli-edit or join/split stuff to get UV maps done.

Hmm.. might have to do some performance testing to see if there is any noticeable hit in a real-world scenario; that will be the deciding factor, though I doubt I'm going to notice anything appreciable on my hardware for a couple of extra draw calls. Looking into a few other part-mods a bit, I can see both methods being used (atlasing multiple parts, and single tex for re-used faces), and I've never noticed any performance hit from those...

Thanks again for your help... have some rep