[darwins]

I did post this in a previous thread, but still do not know the answer.

Do we need Levels of Detail in models in OR or does the OR software decide what it draws depending on distance without the need for these?

[ebnertra000]

LODs are almost certainly still required. How else would OR know what should and shouldn't be drawn at a given distance

[darwins]

Just wondered if the drawing was intelligent to think about size and distance.

Possibly as things were further and further from the viewer polys might be omitted, starting with the smallest and then getting progressively larger.

I need to work out what is good practice for OR and what is not as I start to look at building for OR rather than MSTS.

[wacampbell]

Open Rails responds well to having LODs. But there is no need to over do it.

For example if you have a model that renders in a single draw call ( eg 1 texture, 1 material ), and its under about 500 triangles, thats as low as you need to go. There's little value in making a 200 or 100 triangle LOD. It takes modern GPUs about the same amount of time to render 500 triangles as 100 triangles due to their parallel processing.

If you have a model for example, 2000 tris, and 5 draw calls. Then its great if you can add one LOD to get it down to the 500 tris/1 draw call level.

If you are at 10000 tris, then maybe two LODS are in order at 2000 tris and 500 tris

None of this is carved in stone - these guides are just from my own practical experience.

[Genma Saotome]

Right now the correct strategy to follow also depends on the combination of how many instances of the model are placed in the same scene and you've activated instancing. In that case the LOD's are pretty much ignored and all of the placed instances are drawn at once. That does save a lot of work... n models being drawn as-if they were only 1, but the code ignoring their LOD's is counter-intuitive to the model creator.

I agree w/ Wayne's comment that if you can use an LOD to cull one or more drawcalls from a complex model you have an ideal situation for using LOD's.

Last, because of OR's extended view distances models will display at much further distances than in the old MSTS days and there will be a whole lot more models being displayed as well. Recall that few to none of those MSTS models were created with that reality in mind and so with that said I'll suggest there is a legitimate need for more than one or two LOD levels... quite a few polys and drawcalls can be culled from large models in ranges between 2000m and 10000m.

[darwins]

Thanks for the comprehensive answers.

Quote

Right now the correct strategy to follow also depends on the combination of how many instances of the model are placed in the same scene and you've activated instancing.

How do we activate instancing?

Does it work for trains as well as scenery objects?
Presumably if so it would only work for identical shapes - so if we wanted to have a rake of similar carriages with different numbers - then those would presumably be better added as a freight anim. to a common shape...

[Hamza97]

Unfortunately, AFAIK, instancing doesn't work on rolling stock at the moment, so 5 same wagons will be x5 processing only, not x1 processing....

[Guille592]

I have some trains I made myself with way over 40k polygons and more and no LODs on the train. I just simply introduced a distance of 2Km and with a dual core PC I can move it without any hesitation.

[Goku]

Guille592, on 02 February 2018 - 06:23 AM, said:

I have some trains I made myself with way over 40k polygons and more and no LODs on the train. I just simply introduced a distance of 2Km and with a dual core PC I can move it without any hesitation.

If you have only one - two shapes in your activity, then you can ignore LODs. But remember that if you want to use this shape in AI traffic then LOD is very important.

[espee]

If you make a model for yourself, and never intend to release it to the public, don't run it in an activity, don't use it as an AI etc etc and can live with lower frame rates, then you don't need LOD's...

[Genma Saotome]

darwins, on 01 February 2018 - 01:58 PM, said:

• How do we activate instancing?
  
• Does it work for trains as well as scenery objects?
  
• Presumably if so it would only work for identical shapes - so if we wanted to have a rake of similar carriages with different numbers - then those would presumably be better added as a freight anim. to a common shape...

1. It is an option you can set in one of the tabs on the OR menu. I don't recall now which tab so I suggest looking at experimental first.

2. No rolling stock, just static objects AFAIK.

3. Yes, the shapes have to be identical, including the textures. Instancing 50 identical trees on the same tile will be handled as-if they were just 1. There is an unknown maximum of placed, identical objects. I have a section along a river that includes rip rap along the roadbed. There are too many identical shapes there and the result is the boulders jump up and down in OR. I have to go and rename a bunch of them to get fewer of the same .s file name. A bother but in the end the rendering cost will still be vastly less that if all of those placed models were rendered one by one.

[Genma Saotome]

espee, on 02 February 2018 - 07:48 AM, said:

If you make a model for yourself, and never intend to release it to the public, don't run it in an activity, don't use it as an AI etc etc and can live with lower frame rates, then you don't need LOD's...

:rotfl:

[Genma Saotome]

I'd like to add that there is an understandable ratio between your screen resolution and what any given width is equal one pixel at set distances from the camera. IIRC at 1920x1080 (or 1200) one inch of model width is one pixel at 125m view distance, which means a 4inch width is one pixel at 500m, 8inch width is one pixel at 1,000m, 16 inches at 2000m and 80 inches is one pixel at 10,000m.

I tend to use a 100m view distance instead of 125, just to keep it simple.

Using that guideline (plus my use of 100m instead of 125) to set LOD's means a 33" freight car wheel is just 2 pixels at 3300m. Perhaps an LOD at that distance, perhaps an LOD at some distance less than that... the wheel is 4 pixels at 1650m, 8 pixels at 825. The "answer" is obviously a judgement call. My point is knowing this ratio lets you make well reasoned decisions consistently when it comes to setting up LOD's in your model.

[Guille592]

espee, on 02 February 2018 - 07:48 AM, said:

If you make a model for yourself, and never intend to release it to the public, don't run it in an activity, don't use it as an AI etc etc and can live with lower frame rates, then you don't need LOD's...

That's curious, cause I've distributed for some friends, we have done multiplayer and or I have activities with AI, and I really don't get much problems. :/

[darwins]

Reading all this, I can see not only a need for LoD, but also a need for lower poly trains for static stock and AI trains - especially for busy routes with full sidings.

Having said that I am thinking of making some "lower poly" models, which still have a more polys than some of the low poly MSTS stock of the past, and make better use of textures and materials.