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Does SL suport different textures & UVmaps per LOD ?


Gaia Clary
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LoDs, as far as I'm aware, always use the UV map you specify for them.  If you don't specify, it appears to auto calculate the new UV based on the vertices it removes when auto chopping your mesh for lower LoDs.  If you make your own LoDs you could effectively make a different UV map for each level.  But... Why?!  >D

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"Do different LOD meshes for an object always reuse the textures made for the highest level of detail ?"

Yes. The LOD meshes must have the same number of materials/submeshes/faces. For Blender* exports, at least, the face indexes are derived from the order of the <triangles> tags in the Collada file. This is always the order of the material indexes in Blender. Collada references to material IDs don't count. So you have to make sure you use the same material index (or texture) for each submesh that is to receive the same texture.

"Or can we have individual textures/UVmaps for each level ?If so how can we associate the texture to the LOD-mesh ?"

No you can't. If you want to use a texture on a low LOD that you don't use on the high LOD (such as the alpha textures I use for my windows' low LOD), you can add a hidden triangle at the high LOD to put it on. (The format documentation says that you can have submeshes with zero triangles, but I can't think of a way of maiking them in Blender, or of texturing them inworld). To put the texture on the hidden face, either set renderVolumeLODFactor to 0.1 so you can see it, or texture the whole thing with it before applying the high LOD texture(s) to individual selected faces. That should not be necessary if you upload with textures, but I never do that.

*That is Blender 4.29, at least.

PS. I have no real evidence beyond my own experiments for all this, and I never tried uploading with different textures specified for the low LOD meshes. Maybe you could try that out and correct me if this is wrong. I would be surprised but accepting.

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Feynt Mistral wrote:

If you make your own LoDs you could effectively make a different UV map for each level.  But... Why?!  >D

I was wondering if at some level of detail the textures for the high LOD just won't fit any longer and needed to be changed to avoid a texture jumping. But what Drongle has answered also makes sense to me.

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Well as far as I know most people reuse their higher grade texture for lower LoDs to a certain point, but in game design at least there are some artists who make their own MIP maps to optimize for different ranges.  This uses the same texture, but with different UV coordinates at different LoDs specified by hand at model creation time.

 

As for a zero triangle "face" you can create a quad (attached to other parts of a mesh), then select all the vertices of that quad in edit mode and delete the face (X, choose Face).  You should then be able to unwrap that quad to a separate map, though obviously it'll be kind of weird.

 

Edit:

The UV map will always be as you made it, and if you remove geometry from the mesh but still keep the UVs, it'll be arranged the same way as before.  At a certain point you'll look at it and say "you know, that baked underboob doesn't look so good with my medium LoDs' pyramid boobs...", but at that point you're either doing as above (MIP maps of your own) or not destroying important geometry to preserve the map longer (becaues underboob is srs bizniz).

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Yes. I nearly always use the same texture, with hand-made UV maps for each LOD, but the window is a special case. To get a really simple lowest LOD, it is just a single alpha texture on two (opposite side) planes. At high LOD it has solid frame and bars. Now you can do that with one texture, but there are reasons not to. I think I decribed this somewhere ... yes, here.

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