Blender Git Loki

Material Preview: Fix Sphere object (squared UV and poles)

A good sphere preview material has a 1:1 UV ratio (so we see squares as
least distorted as possible), as well as good poles.

Square UV:
The original sphere expected a 2:1 panorama to be mapped to it. This
patch changes that (I scaled Y by 0.5) so that square textures look ok.

Poles:
The original sphere had a low initial resolution, so no ammount of
subdivision would fix the poles.

The sphere has a subdivision modifier with 0 resolution. Later (3.1?) I
want to try to change the resolution on-the-fly based on whether the material
has a displacement map.

Old sphere (1.9K vertices):
{F11845752, size=500px}

New sphere (2.0K vertices):
{F11845710, size=500px}

Differential Revision: https://developer.blender.org/D13309