Mitsuba variant "scalar_spectral_polarized" not found

[gioarma]

I'm following the basic example for polarized rendering. I compiled the system following the instructions, and modified the mitsuba.conf file in this way:

"enabled": [
        "scalar_rgb", "scalar_spectral", "cuda_ad_rgb", "llvm_ad_rgb", "scalar_spectral_polarized", "scalar_rgb_polarized"
    ]

In my notebook I first run

import mitsuba as mi
mi.set_variant('scalar_spectral_polarized')

and I get no error, so I guess the system is properly recognizing the poloarized variant.

However, when I import the cbox_pol.xml scene I get the error reported below. I did not modify in any way the .xml file, it is exactly the one provided on the website.

scene = mi.load_file('Scenes/cbox_pol.xml')

---------------------------------------------------------------------------
ModuleNotFoundError                       Traceback (most recent call last)
File C:\Program Files\mitsuba3\build\Release\python\mitsuba\__init__.py:107, in MitsubaVariantModule.__getattribute__(self, key)
    104 with _dr.scoped_rtld_deepbind():
    105     modules = (
    106         _import('mitsuba.mitsuba_ext'),
--> 107         _import('mitsuba.mitsuba_' + variant + '_ext'),
    108     )
    110 super().__setattr__('_modules', modules)

File C:\ProgramData\Miniconda3\envs\mitsuba_rendering\Lib\importlib\__init__.py:126, in import_module(name, package)
    125         level += 1
--> 126 return _bootstrap._gcd_import(name[level:], package, level)

File <frozen importlib._bootstrap>:1204, in _gcd_import(name, package, level)

File <frozen importlib._bootstrap>:1176, in _find_and_load(name, import_)

File <frozen importlib._bootstrap>:1140, in _find_and_load_unlocked(name, import_)

ModuleNotFoundError: No module named 'mitsuba.mitsuba_scalar_spectral_polarized_ext'

During handling of the above exception, another exception occurred:

AttributeError                            Traceback (most recent call last)
Cell In[12], line 1
----> 1 scene = mi.load_file('Scenes/cbox_pol.xml')

File C:\Program Files\mitsuba3\build\Release\python\mitsuba\__init__.py:253, in MitsubaModule.__getattribute__(self, key)
    251     sub_suffix = '' if submodule is None else f'.{submodule}'
    252     module = _sys.modules[f'mitsuba.{variant}{sub_suffix}']
--> 253     result = module.__getattribute__(key)
    255 # Add set_variant(), variant() and variant modules to the __dict__
    256 if submodule is None and key == '__dict__':

File C:\Program Files\mitsuba3\build\Release\python\mitsuba\__init__.py:113, in MitsubaVariantModule.__getattribute__(self, key)
    111 except ImportError as e:
    112     if str(e).startswith('No module named'):
--> 113         raise AttributeError('Mitsuba variant "%s" not found.' % variant)
    114     else:
    115         raise AttributeError(e)

AttributeError: Mitsuba variant "scalar_spectral_polarized" not found.

[wjakob]

You need to compile this variant yourself -- it's not one that we ship by default. Please read the documentation on how to make builds with additional variants of the system.

[gioarma]

Hello, thanks for your answer
I already followed all the instruction at the Compiling the System page, and I'm getting the error reported above.
I looked for the documentation for building specific variants, but I did not find it.
I'm sorry but I'm not familiar with building with cmake

Any help is appreciated, thanks!

[merlinND]

If your custom Mitsuba build succeeded, then the most likely issue is that import mitsuba as mi picks up another version on your PATH (e.g. one installed via pip).
You can print mi.variants() and mi.__file__ to check whether they match your custom build.

[gioarma]

Thank you, I finally understood what I needed to do. My understanding was that all variants were installed by cmake, and I just needed to specify the ones I wanted to use in the mitsuba.conf.
Instead, cmake builds only the variants specified in the mitsuba.conf file. So, if one wants to add a new variant they need to change the mitsuba.conf file adding the desired variant, and then run again cmake to build again the whole thing.

[njroussel]

👍 This is the relevant part of the documentation.