What are sections?

[Double Doppler]

I have been using O2 for quite some time now with some success, but I haven't found a good explanation about Sections. What are they? How are they related to model performance and what is the desired amount of sections in a model per role? My game's FPS is lower when I spawn numbers of my car as opposed to BIS stock ones. Its sections are around 30.

[[FRL]Myke]

Hopefully someone who can explain it better will hop in very soon but in the meantime, i'll give it a try.

If i had it understand correctly, for every section, the GPU has to "switch" it's mode (whatever that means), it loses some cycles in which no calculations can be made. So loss of performance.
A "section" is often a part with a new textures. So let's say a cube with 2 independent textures might have 2 sections. Same cube with only one texture but 2 different rvmats will also have 2 sections. Same goes for 2 textures and 2 rvmat's (given that the rvmats cover the same faces as the textures).

So a effective way to reduce sectioncount is to merge separate textures into one (if possible) single texture. same goes for the rvmat aswell, ofc.

I've also heard that smooth edges/sharp edges can increase sectioncount but there, don't ask me how and how to reduce it.

[Max Power]

As I understand it, a section is, for our purposes, a material/texture combination. Everytime you have a different texture or material on a polygon, it's in a different section from the others. Each section requires a different draw call. As [FRL]Myke says, initiating new draw calls eats up cycles which in turn eats up performance. Section and draw calls are extremely important to consider. Community tests and developer information point to it being perhaps the most important consideration. It is generally better to have one large texture map instead of several small ones. That said, making one giant texture map can be a real PITA, so perhaps it must be balanced with ease of painting, and therefore development time.

[STALKERGB]

How are they related to model performance and what is the desired amount of sections in a model per role?

Desired amount for any model will always be as low as possible, for infantry models that is normally from about 4 to 10. After having a quick look at some BIS samples from ARMA1 the vehicles tend to be 15 or less. (But dont take my word on that!)

As with everything, it varies from case to case.

Interestingly, the BIS Hilux model has 29 sections which sounds very high to me. Or at least in the ARMA1 samples it does...

In terms of lowering the count, one tip I use is putting an existing texture/material onto any proxies in use. Should knock the section count down by 1 if nothing else

[Synide]

A Section = unique texture/rvmat combinations mapped to faces in the given LoD.

More sections = more drawcalls, less sections = less drawcalls.

For example you may have a cube with six faces. All the faces are mapped to the texture... 'fat_dice_co.tga'. If you also mapped each individual face to a different .rvmat then there would be '6 Sections'. They're are 6 unique texture/rvmat combinations. However, if you condensed all the face texture/rvmat mappings down to 'fat_dice_co.tga' & 'fat_dice.rvmat' then you'd have 1 Section.

How do you reduce sections? By merging textures. Usually, in doing so you increase the physical dimensions of your textures at the same time to keep some texel resolution.

Its sections are around 30.

To many for a 'car' imo... should be aiming towards 1/3 or 1/4 of that or less if you can manage it.

[Baraka]

Interesting Theme.
What´s with the other textures like the "*_smdi.paa" and the "*_nohq.paa" ?
For example when you have a car with one 1024*1024 "car_co.paa". Then you use some metalic parts and some glas. So you fave 3 times the rvmat textures with 3 different rvmat settings. The loading time for all the textures affect the GPU-Ram mostly AFAIK, the section may cost other GPU Power.

[Max Power]

Like Synide and I said, the section count is related to unique texture and material combinations. So, three distinct materials, applied to polygons that all share the same texture, makes three sections. GPU ram usage, mip maps, texture sizes, number of material textures, etc do affect performance but are not related to section count.

[STALKERGB]

What´s with the other textures like the "*_smdi.paa" and the "*_nohq.paa" ?

Those are textures which often make up part of the RVMAT. So for example you could have Car.rvmat which is made up of car_nohq.paa, car_smdi.paa and car_as.paa.

[Baraka]

@STALKERGB,
I know that, but i asked myself if the math behind the Shaders needs more GPU-Power then the single Textur.
Also i was not sure if the sections for textur-sources are the same thing like the parts in the 3D Mesh.

[Max Power]

I believe normal maps require more resources than other maps. At any rate, all of the maps are loaded into video memory at some point.