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Fix T94516: OBJ/MTL Material Roughness imported and exported inaccurately. 

The addon would assume an OBJ range of [0.0-900.0] for the Ns value,
when it actually is supposed to be [0.0-1000.0].

WARNING: This is introducing a slight incompatibility (value shifting of
the roughness parameter) with older OBJ files exported by Blender.
This commit is contained in:
Bastien Montagne 2022-01-10 11:20:59 +01:00
parent 29c03b6570
commit f26299bacc
Notes: blender-bot 2023-02-14 18:27:04 +01:00 
Referenced by issue #94516, OBJ/MTL Material Roughness imported and exported inaccurately.
3 changed files with 9 additions and 8 deletions
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4
io_scene_obj/__init__.py
View File

@ -21,8 +21,8 @@
bl_info = {
"name": "Wavefront OBJ format",
"author": "Campbell Barton, Bastien Montagne",
"version": (3, 8, 1),
"blender": (2, 81, 6),
"version": (3, 9, 0),
"blender": (3, 0, 0),
"location": "File > Import-Export",
"description": "Import-Export OBJ, Import OBJ mesh, UV's, materials and textures",
"warning": "",

7
io_scene_obj/export_obj.py
View File

@ -74,9 +74,10 @@ def write_mtl(scene, filepath, path_mode, copy_set, mtl_dict):
use_transparency = mat_wrap.alpha != 1.0
# XXX Totally empirical conversion, trying to adapt it
# (from 1.0 - 0.0 Principled BSDF range to 0.0 - 900.0 OBJ specular exponent range)...
spec = (1.0 - mat_wrap.roughness) * 30
spec *= spec
# (from 1.0 - 0.0 Principled BSDF range to 0.0 - 1000.0 OBJ specular exponent range):
# (1.0 - bsdf_roughness)^2 * 1000
spec = (1.0 - mat_wrap.roughness)
spec *= spec * 1000
fw('Ns %.6f\n' % spec)
# Ambient

6
io_scene_obj/import_obj.py
View File

@ -361,9 +361,9 @@ def create_materials(filepath, relpath,
context_mat_wrap.emission_strength = 1.0
elif line_id == b'ns':
# XXX Totally empirical conversion, trying to adapt it
# (from 0.0 - 900.0 OBJ specular exponent range to 1.0 - 0.0 Principled BSDF range)...
val = max(0.0, min(900.0, float_func(line_split[1])))
context_mat_wrap.roughness = 1.0 - (sqrt(val) / 30)
# (from 0.0 - 1000.0 OBJ specular exponent range to 1.0 - 0.0 Principled BSDF range)...
val = max(0.0, min(1000.0, float_func(line_split[1])))
context_mat_wrap.roughness = 1.0 - (sqrt(val / 1000))
context_material_vars.add("roughness")
elif line_id == b'ni': # Refraction index (between 0.001 and 10).
context_mat_wrap.ior = float_func(line_split[1])