Incorrect render when texture coordinates are zero

For some triangles I have u=0, v=0 for all vertices. In this case the textures are dispayed incorrectly if WrapS/WrapT stated as “Repeat”. If I switch to “Clamp” - the texture looks fine.

I tried a lot of formats - it happens in all of them. I observed the same behaviour when importing to blender.

How can I fix it other than by manually switching ?

I’m not sure I follow, if the UV coordinates are the same everywhere, it’s expected that a texture does not show, right?

I am not aware of it. As far as I understand - if all UV coordinates equal to (0,0) - the texture should still be shown - but the whole triangle should be colored as a pixel in the left/low corner (or other corner depending on the system).

Right, but as the UV coordinate is the same for every triangle, they’ll all have the same color, no?

They do, but not the pixel in the corner - they choose some pixel from the middle.

Hi @brand17
Could you share the URL of the model having this issue ?

If the problem is also visible in Blender, it means that your authoring tool might be exporting a different data than the one you set. Which tool are you using ?

Hi,

URL is https://sketchfab.com/3d-models/archiveforuploading-9b6e0573be7b476f9f478104473743fb.

For bark material UV1 - UV second coordinate (V) is zero for majority of vertices (all except young thin branches). It is done to be able to color young thin branches by green - I apply green gradient texture (it is included in the model). But unless I set Wrap T as “Clamp” - it is displayed incorrectly - think branches are green (should be black), some thin branches are black (should be green). After setting Wrap T to “Clamp” - it is displayed right.

More simple example is here - https://sketchfab.com/3d-models/from-blender-2ce9df032d934809a69c0c3e30d23aa9

The models are prepared in my app. I export them using assimp library. For simple model I see that UVs are zero in dae file.