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enter image description hereWhen I do unwrap in blender 2.78 I get like this. With strange triangle diagonal line - what's this?

How I can get smooth linear interpolation?

Thanks!

P.S. Post edited - change to more evident gif demo.

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The diagonal line comes from the way you unwrapped the plane.

Bad Unwrap

  1. What you need to do is to push 7 to go to top view.
  2. Then push 5 to go to orthographic view.
  3. Lastly choose project from view bounds.

Before:

Bad unwrap before

After:

Bad unwrap after

EDIT: I misunderstood the question. The solution you are looking for is just to subdivide the plane. See this for why.

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  • $\begingroup$ If I understood correctly, the problem was not the shape in the uv map, but how the texture is projected on the mesh. It is not as uniform/smooth as expected. I had a similar (unsolved) problem when trying to match the sides of a non-rectangular quad, to texture a circular mesh made of trapezes. $\endgroup$ – Cebbi Jun 14 '17 at 12:31
  • $\begingroup$ @Cebbi The problem (if this fixed it) was the shape of the UV map. The UV map is what determines how the texture is laid out on the mesh. Project from view bounds just changes the UV map to a nice square (The shape of your texture). $\endgroup$ – Striar Jun 14 '17 at 12:38
  • $\begingroup$ Instead of interpolating the coordinates, the face is split into triangles with different kinds of stretching, so there is a visible seam connecting two vertices: i.stack.imgur.com/jdSy1.jpg In the left part, the UVs are not stretched at all, so the edges of the texture don't match. On the right side, the UVs are stretched to a square, but it's now ugly inside the face. $\endgroup$ – Cebbi Jun 14 '17 at 16:54
  • $\begingroup$ @Cebbi Ah I get what you are asking now. I did some testing and posted a question here: blender.stackexchange.com/questions/81380/… $\endgroup$ – Striar Jun 14 '17 at 17:25
  • $\begingroup$ @Cebbi, yes you understood correctly. I can qet square unwrap like answer, but when i scale two vertexes (two on top) in X axes - I get strangle triangle scale, instead smooth linear scale and mapping texture on mesh as I show in second picture. $\endgroup$ – tdhster Jun 14 '17 at 17:48
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Answer from blender developer team:

This is not really a bug, but rather a known limitation of Blender's UV mapping algorithm. Unfortunately there is not much we can do about this, short of rewriting the whole UV mapping system. You can however minimize the issue by subdividing your mesh a few times.

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