I’m working on the optimization of my objects using the statistics profilers
and reading the SDK relevant section. Both encourages us to use smaller
textures on lower lods, even 64x64 pixel sized textures on the LODs which are
less than 5%. Is this really needed? I have checked the converted DDS
textures. They all contains MipMaps. Are the mipmaps ignored by MSFS? I’m just
asking if this really neccessary to define almost for each LOD a new material
and to add additional textures increasing the overall loaded material and
texture numbers. Thanks a lot!
I have made a small experiment. I have opened one of my converted DDS texture
in the package. Edited only the 2nd mipmap (some red criss-cross) with GIMP
and saved it. It does seem that the MipMap is indeed used in the simulator and
working fine. Nice smooth transitions from far to close rendering. Look at the
screenshots. The red “scribbling” appears only at a certain distance. I think
it is crucial to make a statement on this matter because in my opinion to
create additional materials and textures for each LOD leads to a contradictory
effect in optimization.
Hi, Using lower-resolution textures is not to reduce texture sampling cost, it
is to reduce overall memory usage. It is theoretically possible (albeit rather
complex) to dynamically stream the required mipmaps from disk, but this is not
a feature we have at the moment. For memory optimization, there are a few key
elements:
- it is important that lower resolution LoDs use less memory
- multiple (or even all) LoDs may be loaded and displayed at the same time, thus exist in memory at the same time
Consider two different cases.
- You have a model which exists only once in the world. In this case, only one LOD will persist in memory. To facilitate fast loading/unloading of the model, it helps if the textures are shared between the LODs. For memory purposes, this is not as important, but it can still help to reduce memory spikes when streaming in LODs.
- You have a model which exists multiple times in the world. Think of multiplayer aircraft, or props such as lanterns. In this case, multiple LODs may persist in memory (the model can be displayed far away and close by at the same time). To reduce the total memory footprint, it is crucial that textures are shared as much as possible between the LODs. At the same time, if the model is only displayed once, but far away, you want a small memory footprint. If vertex coloring does not cut it, and you need a texture for a faraway model, having a small texture (instead of some 2k maps you may have) can help reduce memory usage.
A final note. You say: “to create additional materials and textures for each
LOD leads to a contradictory effect in optimization”. In reality, due to the
way our engine (and the LOD system) works, materials are not shared between
different LODs, only textures. As you say, to create additional textures seems
contradictory. I believe duplicating textures should only be done if texture
memory for a given LOD can not be reduced through different means. For
example, simply by removing textures from a material, or using vertex colors.
Vertex color is great, as it is practically free . In the documentation,
it currently says:
Prefer low-resolution textures for LoDs below the approximate 5% “minSize”,
eg: try to keep this as 64x64px or smaller.
We will change this to be a bit more clear on the intention behind it:
When reducing texture memory for lower resolution LODs, if it is not
possible to remove more textures, use lower resolution textures instead (and
make them small, e.g. 64x64px or smaller).
Thanks for your answer! If I understand it well the main object should be to
reduce the memory used by textures. Just to clarify when I talk about textures
I always mean base color texture. For me a crucial question here if the
texture gets unloaded from the memory if it is not used at the scene at the
moment? What I mean by that if I add a separate lower res texture to a smaller
LOD but the view comes closer and larger LOD with larges texture gets loaded
is the smaller res texture unloaded from the memory?
yes, the smaller resolution texture will be unloaded if it’s not used by
another instance of your model or by another model
I would think replacing textures with colors would be best for the more
distant LODs if possible.
absolutely 
as I said in my answer: " duplicating textures should only be
done if texture memory for a given LOD can not be reduced through different
means " “different means” including vertex color, for sure!
I see the default POI objects in the sim do not use smaller textures for
different (smaller) LODs. But this might make sense as they are placed once in
the sim as noted above.
- You have a model which exists only once in the world. In this case, only one LOD will persist in memory. To facilitate fast loading/unloading of the model, it helps if the textures are shared between the LODs. For memory purposes, this is not as important, but it can still help to reduce memory spikes when streaming in LODs.