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I'm using an UV map node for some cycles materials, both being generated by a script of mine. Everything is OK in the viewport and in renders but in the material preview tab it appears with an uniform color corresponding to the right border of the texture. As soon as I disconnect the UV map node from the diffuse texture, the preview is OK again. If I reconnect it the preview shows again an uniform color. It this so for the Diffuse shader or the diffuse entry in the principled shader.

If I play with the UV mapping, either with the mapping node or the mapping in the Properties -> Texture tab, it seems that I can change the position but in the preview pane any change in the size seems to not have any effect.

I suspect UV mapping used for the viewport & render are not the same than for material preview.

So the question is "why the preview show only the color on the border of the texture while what can be seen in the viewport or in renders is OK since it corespond well to the texture and the UV map"?

bad preview

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  • $\begingroup$ tbh it's a bit difficult for me to spot those differences, maybe I didn't understand. It would be useful if you could show images to better undersand $\endgroup$
    – m.ardito
    Oct 18 '17 at 21:09
  • $\begingroup$ @m.ardito I'll (tomorrow) but the problem, as can be seen in the blend file, is that on the object 'KO', the preview is all purple while it should show the UV grid as in the viewport and in renders. $\endgroup$
    – lucvoo
    Oct 18 '17 at 21:55
  • $\begingroup$ oh sorry I completely missed the point :) I'll add an image below to show what I tried (not a real answer) $\endgroup$
    – m.ardito
    Oct 19 '17 at 8:12
  • $\begingroup$ @m.ardito thanks. Yes, as far as I understand, using the UV from the Texture Coordinate node or leaving the UV input unconnected should be identical: use the UV coordinates from the 'active UV render layer'. But what is a 'UV render layer', isn't the same as the UV map? $\endgroup$
    – lucvoo
    Oct 19 '17 at 13:51
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    $\begingroup$ The issue is that the preview doesn't know what KO UV map is. The preview window sphere only has a single UV map, and it uses only UV called "UVMap". Shouldn't be a big deal-- if you want to see a preview, make a sphere and give it a "KO" UV map. $\endgroup$
    – Nathan
    Jan 1 at 2:11
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Here I tried another node to see the difference

enter image description here

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