unity-game-enginerenderingtexture-mapping

is non-square tilable atlas effective

I have a building model with 6K faces and I want to texture with some pretty high detail 512x512 tilable textures (which represent about 32cm x 32cm), and I'd like to be as mobile-friendly as possible, but not necessarily with old phones but for like GearVR capable phones.

The model happens to have mostly long horizontal quads eg

|-----------|---|----------------|
|-----------|---|----------------|
|-----------|   |----------------|
|-----------|   |----------------|
|-----------|---|----------------|
|-----------|---|----------------|

So the uv's of each of those horizontal sections can be stacked on one tileable texture, to achieve both horizontal and vertical tiling.

Further, if the tiles were 512x512 textures, I could stack 8 of them in a 512x4096 non-square (but power of two) texture.

That way I could texture the main mesh with a single texture or one extra for metalic.

Is this reasonable, or should I keep them as separate 512x512 textures? Wouldn't separate textures mean like 8x the draw calls which would be far worse than a non-square 512x4096 texture?

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Solution

  • After some research, I found the technique of stacking textures and tiling horizontally is called using a trim sheet, and is very much valid, and used extensively game development to be able to re-use high-detail textures on many different objects.

    https://www.youtube.com/watch?v=IziIY674NAw

    The trim sheet info I found though did not cover 'non square' which is the main question. But from several sources I found that some devices do not support non-quare and some do, and some do but don't do compression well on non-square, so it's a 'check your target devices' issue.

    Assuming a device does support non-square, it should in fact save memory to have a strip of textures, and should save draw calls, but your engine may just 'repeat them horizontally until square' for you when importing the texture to 'be safe' (so again, check target devices and engines). It would perhaps be wise to limit to 4 rather than 16 stacked textures, to avoid 'worst case scenarios'.

    Hopefully, the issue will be addressed by either having video cards able to do several materials in 1 draw call, or by more universal handling the texture strips well, but it seems state of the art has not focused on that yet.

    Another solution is more custom, but some people have created custom shaders that use vertex color information on a mesh to choose which part of a texture to use, and then tile from there. Apparently the overhead turned out to be quite low, and it was a success, so it's good to have an idea about 'backup plans'. This however would be an engine/environment/device specific kind of optimization, not a general modeling practice.

    https://www.gamedeveloper.com/programming/unity-optimizing-for-mobile-using-subtile-meshes