Multiple faces/materials vs just one... does it matter?

[Rick Nightingale]

Apologies that my knowledge on this is vague (and my memory isn't too good*). I seem to recall reading that multiple materials/faces on a mesh cause the viewer to have to split the mesh into multiple parts and render them separately... is that the case? If so, how much does it really matter in the grand scheme of rendering a scene? Is it a case of six materials, say, takes six times longer to render than one? Or is it insignificant?

I'm making something that I could split into six materials, easily UV mapped for others to re-texture, or I could map the whole lot onto one complex UV map and a single material. That's not so nice for re-texturing. For supplied version I would still map the individual faces onto a single texture in-world to save texture memory and downloads; that's not the question.

I guess those who really know the internals of viewers can answer this the best...

Of course, I will do whatever the item (or rather its buyers) needs, but there are many cases where I could pick either because I'm making for myself. If a single material is much more efficient, I would go for that.

*Not joking... I lost most of three days' memory the weekend before last, from Saturday to Monday evening. Only really recovered fully a few days ago. Yet another MRI scan is pending... unless I forget.

Edited May 2, 2023 by Rick Nightingale

[benchthis]

I hope you're feeling better. Neat question. I'm not too sure about how performance factors into number of assigned materials per object. Anytime I build anything I will always try to use all the material allowances in the most logical way because it makes objects in world more modifiable. The more modifiable objects are in world the more useful they are, to me at least. There has been desire from community to have the maximum number of materials increased per object without object breaking. 

[ChinRey]

1 hour ago, Rick Nightingale said:

I seem to recall reading that multiple materials/faces on a mesh cause the viewer to have to split the mesh into multiple parts and render them separately... is that the case?

That is usually correct. However, the viewer will try to consolidate draw calls for regular meshes, prims and sculpts but not (and this is important) for fitted mesh. So if there are several faces with the same texture and other surface properties in a scene, they should be handled as a single draw call.

1 hour ago, Rick Nightingale said:

If so, how much does it really matter in the grand scheme of rendering a scene?

The number of draw calls matters a lot but compare a mesh with six faces/draw calls to a mesh avatar where each and every alpha cut needs its own draw call!

Besides, splitting a mesh into several faces have a couple of potential advantages when it comes to render efficiency. Splitting adds more opportunities for using using tiled textures for a start, and with them you can get much higher resolution with smaller textures; there can be a lot to save that way. Using simple "single purpose" textures also means there are more chances you can re-use the same textures for multiple objects, you have more ways to create variety by using the same mesh with subtly different tints or different textures. All of these are factors that will reduce the render load.

There are certainly way too many meshes with single baked textures in SL today but that doesn't mean it is always better to go back to the good old multiface tiled texture method. It depends on several factors and in the end it's all up to the individual builder's good judgement - or lack of such.

Edited May 2, 2023 by ChinRey

[Rick Nightingale]

22 minutes ago, ChinRey said:

Splitting adds more opportunities for using using tiled textures

Yes, I do like to do that, and it is exactly one of the decisions I'm making in the current build. Sometimes I've done that, on parts that I don't want to give their own face to, by extending the uv map for the part multiple times wider than the texture. Skirting boards and other long trim parts spring to mind.

Everything you said makes sense to me. Thank you!

[Kyrah Abattoir]

Less is always better, but you have to balance it, sometimes separate surfaces allow you to make huge texture usage reductions for instance.