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Backface colors flipped when using different and custom backface shading

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python

Research direction

Start by running the Python MWE with the supplied bunny_oded.obj mesh and selecting backface shading → custom. Trace the backface-shading path responsible for choosing the front and inverted colors, then verify that the mesh displays the correct custom backface colors without treating all faces as inverted.

Written by the indexing model from the issue text.

Description

Hi!

I am using polyscope in python on my intel Mac. When I read this mesh and choose the "backface shading -> custom" option, all faces assume the "inverted" color, despite this mesh being definitely not inverted. Here's a MWE:

import igl
import polyscope as ps
V, _, N, F, _, _ = igl.read_obj("test/unit_tests_data/bunny_oded.obj")
ps.init()
ps.register_surface_mesh("bunny", V,F)
ps.show()

Here is what I see:

Screenshot 2023-07-03 at 11 28 37 PM

Dominant language
C++
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Merged PRs (30d)
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