Why does an even subdivide change the displayed texture? In my scene I have a default plane and scaled one edge along the x axis. I have a material that is just a tile texture that is mapped on with a UV map. Here is a screenshot of the setup.



This is far from what I would expect. I would expect that it would look like the tiles had been compressed. My expected result shows up as I subdivide the plane. What is subdivide doing that is fixing this mapping?

Here is 1 subdivision


Here is 3 subdivisions
Ah I figured it out and it's not the vertices. Blender uses a triangulated version of a mesh to do UV mapping.

Looking at this we can see two distinct triangles:



Initially this doesn't make much sense since the object only has 4 vertices and should just compress as if it was transformed in Photoshop. However, once the mesh is triangulated with Ctrl + T the problem is clear.



All of the UV data is equally split between two uneven triangles. Subdividing makes the all of tris closer in size, creating less distortion.