Beginner questions: What all to UV map this symmetrical object
polycounter lvl 3
I used 3D Studio Max to model this and im stuck on what all needs to be unwrapped and what doesn't. I know how to unwrap, but im confused about how and when i can use the symmetry modifier during this process (should i turn it off?) -also how instanced geometry comes into play? Will instanced geometry all unwrap the same and go into a game engine just fine after export into 3ds max? Is it not okay to overlap UVs? I've searched on this almost all day and can't quite find the answers.
Replies
Here's one example of such a tutorial. And another.
To answer the overlap question now:
Generally in a game engine a texture is repeated in both U and V axis of the texture. So if you have 6 identical cylinders you'd unwrap one and duplicate it (so they UV's are stacked). Stacked UV's are only a problem when you go to bake a normal map (and maybe some other stuff); which is why you'll often offset your duplicate pieces by 1 in either U or V or both, because the texture is repeated in those co-ordinates — but anything outside the 0,0 to 1,1 bounds isn't taken into account when baking.
So my basic guess as to how to proceed most efficiently would be:
1.)Delete all instanced geometry and slice symetrical models in half or even quarters (like the barrel) deleting the other halfs.
2.) UV map what is left.
3.) After mapping, copy needed identical geometry as instances ( and their UV's will automatically be overlayed in the existing set and accounted for during obj export? )
Keep in mind that mirroring saves texture space (which is generally a really good idea) but also increases vert count (slightly, because more uv seams = more vert splits — if you don't know what I'm talking about read the 'you're making me hard' sticky in tech talk) and more importantly leads to less interesting textures because you can't have too much detail around mirrored seams, otherwise you get the butterfly effect which is super noticeable.
Those two tutorials I linked are game-art tutorials which for memory show pretty much the whole process, from high to low to bakes to texturing.
Those videos aren't much help IMO. The maker of the gun video won't use any symmetry at all because its intended for the Fallout 3 Vegas Engine and the knife tutorial doesn't use it either, i think because he ends up with text, which im guessing wouldn't look right mirrored.
A) Unwrap one piece of mesh and instance it, go into the UV map and offset the instanced pieces of geometry by 1, and then in the second channel of the UV map (the second half being done in-engine most likely) completely separate all of the mesh pieces so that all pieces have unique space for light map bakes.
Advantage: Fewer UV islands reduces the vertice splits, thereby reducing the draw calls (I'm not certain if this is true of instanced geometry though)
Disadvantage: Extra work once in engine depending on your engine choice
OR
Advantage: Less hassle implementing in-engine depending on choice
Disadvantage: More UV islands to worry about and increased vertice splitting resulting in longer draw call times.
As far as your modeling process goes, using instances and mirrors are OK if, at the end of it, you collapse your modifier stack (save 1 version of the file with all modifiers prior to the collapse and 1 version after the collapse) and weld vertices as necessary to further reduce the vertices showing and splitting in the UV map to achieve smaller draw call time.
*If there is any bad information in here, please correct me but this is my current understanding of the processes*
Pretty much answered all of my questions and right on Polycount too.
Thanks to Sigmfie and Bek for the help too!