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Uploader vs Blender difference between vertices count


Reiramon
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I am trying to upload something but noticed a difference in vertice count shown in Blender vs in the SL upload window.

Blender says I have 378 verts and 548 triangles, but SL uploader says I have 830 vertices and 548 triangles.

Why is there such a big difference in vertices? Nowhere in Blender I can see 830 verts even when I manually triangulate my mesh. 830 is more than double than 378.

The triangle count is correct, where is the uploader getting the 830 vertice count? I dont have any overlapping vertices.

Thanks!

Edit: Only LOD0 vert count matches what I see in Blender vs uploader. Lod3, 2 and 1 show more verts in uploader. 

Edited by Reiramon
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A single vertex can hold multiple kinds of information. Coordinates in XYZ space, coordinates in UV space, vertex color etc. SL counts all of them.

It's the difference between "how many bags are there" (Blender) and "how many things are in all bags" (SL).

Edited by Candide LeMay
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Sharp edges are IMO the most likely cause, they become split when uploaded, and that is not a problem or an error, just a consequence of the SL rendering engine not really having a concept for what is a "sharp edge" so it needs to have the edge and its vertices defined multiple times to break up the otherwise interpolated normals between the faces. For example a cube has 8 vertices, 12 edges, but if you upload one (with sharp edges so it actually looks like a normal cube and not a weird soft shaded lump), it becomes 24 vertices, 12 edges: each vertex is shared between 3 edges, and each edge is split, so vertices get tripled and edges doubled.

Edited by Frionil Fang
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Without pictures we are just guessing. 

The uploader however will split any vertex that is shared between triangles that are in different materials faces. You can test this with a simple cube. 

8 verts/ 12 tris for the cube, but if you set each face to be a different material slot, then it will be  6 submeshes as far as SL is concerned and the verts get split giving you 24 verts and 12 tris.

 

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1 hour ago, Frionil Fang said:

Sharp edges are IMO the most likely cause, they become split when uploaded, and that is not a problem or an error, just a consequence of the SL rendering engine not really having a concept for what is a "sharp edge" so it needs to have the edge and its vertices defined multiple times to break up the otherwise interpolated normals between the faces.

 

15 minutes ago, Beq Janus said:

The uploader however will split any vertex that is shared between triangles that are in different materials faces. You can test this with a simple cube.

 

The third common reason for vertice splits is UV mapping (in SL a vertice can only have one location on the UV map, in Blender multiple).

This is not unique to SL btw, as far as I know all game/virtual reality engines do it this way. This is because it's faster for the render engine to handle vertices with simplified data sets even if it sometimes means there'll be a couple more of them.

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16 minutes ago, ChinRey said:

This is not unique to SL btw, as far as I know all game/virtual reality engines do it this way. This is because it's faster for the render engine to handle vertices with simplified data sets even if it sometimes means there'll be a couple more of them.

yep, in a system where different faces have different rendering needs (go through different parts of the pipeline and end up going to different shaders) ensuring that meshes split easily into their "renderable units" is a pretty standard practice. 

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Exported to *.dae applying modifiers in the export? Bevels got included perhaps?

I haven't noticed this behaviour myself unless I applied modifiers I didn't want, or I saved to the wrong filename (overwriting because of change) and the mesh is a different level than expected :D

eg. Re-exporting but saving an higher level LOD over a lower LOD file by accidentages :D

Edited by Codex Alpha
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On 5/29/2022 at 9:49 PM, Frionil Fang said:

just a consequence of the SL rendering engine not really having a concept for what is a "sharp edge" so it needs to have the edge and its vertices defined multiple times to break up the otherwise interpolated normals between the faces.

When it comes to rendering there IS no such thing as a sharp edge, only two colocated vertices with different normal orientations.

Modeling programs simply go with the assumption that modelers are not interested in the post-split vertex count, which will change constantly, but rather by the effective, total number of control points the model has.

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