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Question concerning LOD distances and how SL processes textures


Azriel Drumheller
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Hi, first off I'm sorry if the answers to these questions are posted in another thread, I thumbed through a few pages and didn't find exact answers.  I have a number of questions for anyone who can help me:

1) Does anyone know the exact camera range of each LOD?  Like for example, how far do I have to pan out with the cam for LOD2, 3, and 4 To kick in?

2) Truthfully, I'm not sure how SL handles the textures off of meshes.  For example, I'm making poly mesh modular wall segments.  Most of the segments use the exact same texture map.  If I put the same map onto all the meshes, will SL read them as the same texture map and therefore load them all the same for efficiency's sake, or will it read each as a separate map per mesh?

3) Unfortunately the way the UV's the UV's are laid out at the moment, I would need different textures for some of the LODs.  I'm thinking of baking an orthographic shot of the asset on a simple poly card for the last LOD.  it would need its own 256 texture though.  I haven't had a chance to mess with different textures for different LODs. is this possible? How bad of a kill to efficiency is this?  Is it more of a resource hog to keep the same model for all 4 levels or to have to load a different texture for each level?

Any input would be much appreciated, thanks in advance!

-Az

 

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ok ....  care of the wiki ..  its as such for question 1

LOD 3-0 - 42 Meters

LOD 2-42- 166.67m

LOD 1-166.67 - 333.3m

LOD 0-333.3 +

 

Question 2

SL sees anything as an asset with a UUID,  so if you use the same texture ,  it will only see it as a UUID and apply accordingly. of course thats for base textures that have nothing  not even shadows.

Question 3

This is where it gets a bit sketchy,  as UV Unwrapping is an art in itself,  but I have found that it is dependent on the software you use as to how it handles UV's.  For ecample ,  I created a Low poly version  and UV Unwrapped it ,  then i just copied that and added more detail,  the base UV will still work on the lower model  and the higher model.  that way  I was able to texture a high rez model and the low poly moly was able to handle the texture.

This is how i handle it ,  others may vary depending on experience,  skill and of course the software package.

Regards

 

Bray

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regarding #3 , both texture and mesh streaming are "fairly" efficient in SL, having gone through many iterations of attempting to reduce lag and improve performance. And I think it's possible to make your 256x256 impostor the lowest LOD (I have no tried this), but one thing that comes to mind is the current "material bug" with meshes, which makes the importer erroneously force you to have the same number of materials on the lower LODs as on the main mesh, or something. Hopefully this will be fixed and is about to go away soon, though.

The workaround people use is to include some degenerate zero-area triangles with each material you need (in the lower LODs) even if it's just an impostor with a texture on it itself.

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Azriel Drumheller wrote:

3) Unfortunately the way the UV's the UV's are laid out at the moment, I would need different textures for some of the LODs.  I'm thinking of baking an orthographic shot of the asset on a simple poly card for the last LOD.  it would need its own 256 texture though.  I haven't had a chance to mess with different textures for different LODs. is this possible? How bad of a kill to efficiency is this?  Is it more of a resource hog to keep the same model for all 4 levels or to have to load a different texture for each level?

Actually it is a bit tricky to use different textures for different levels of LOD. You would need to spend one extra material per LOD to achieve that. For example if you wanted to have 4 textures for 4 LOD's then you would need to create 4 Materials and you have to take care that all 4 materials exist on all LOD's.

While you certainly could do that, the more efficient solution would be to take care that all LOD levels can use the SAME texture. Well, this can sometimes be tricky as well.

You can watch the
where i have shown some details

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Braydon Randt wrote:

ok ....  care of the wiki ..  its as such for question 1

LOD 3-0 - 42 Meters

LOD 2-42- 166.67m

LOD 1-166.67 - 333.3m

LOD 0-333.3 +


Actually the distances of the LOD transitions highly depend on the size of your objects. The numbers in the Wiki are given for a mesh with a Boundingbox Diameter of 10 meters. For smaller meshes the LOD transitions take place earlier.

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1) To a first approximation, the distances for LOD switches are calculated from the object radius ® as r/0.24, r/0.06 and r/0.03. Those are the figures given, as Gaia said, for a radius of 5m. The radius is the distance from the center to a corner of the bounding box. There is some more code that modifies these somewhat. (Some details are in this thread, message 25, but there is probably more).

2) The requirement for materials/textures at different LODs was changed recently. It used to be simply that each LOD had to have the same number of materials. Now (not sure of it's released yet) the lower LODs must use a subset of the materials used by the high LOD, but don't have to use all of them. For this purpose the materials are identified by the "materials" attributes of the <triangles> or <polys> tags in the Collada file. (In Blender, this is the name of the material). Official conformation here.

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Re: question 3 - it's more efficient and lower prim (land impact) cost to use a "billboard" on the lowest detail.  I do that with my plants, two planes in an X arrangement, with a rendered image of my high detail model.  I stuck the excess texture on a hidden triangle buried underground on the high detail version, and swapped the texture IDs on the low detail one, so the billboard shows, and the detailed texture is hidden.  My detailed model is ~600 triangles, and the billboard is 6, which results in a prim cost of around 0.5 (you can link two and it counts as one prim).

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