Can't set the variant "scalar_rgb"

[NhatMinh2208]

System configuration

System information:

OS: Windows-10
CPU: Intel64 Family 6 Model 165 Stepping 2, GenuineIntel
GPU: NVIDIA GeForce RTX 3060 Laptop GPU
Python: 3.9.18 (main, Sep 11 2023, 14:09:26) [MSC v.1916 64 bit (AMD64)]
NVidia driver: 546.12
CUDA: 12.3.103
LLVM: -1.-1.-1

Dr.Jit: 0.4.4
Mitsuba: 3.5.0
Is custom build? False
Compiled with: MSVC 19.38.33133.0
Variants:
scalar_rgb
scalar_spectral
cuda_ad_rgb
llvm_ad_rgb

Description

I try new integrator with a scalar variant, something like this:

import mitsuba as mi
import drjit as dr
mi.set_variant('scalar_rgb')

class SomeSamplingIntegrator(mi.SamplingIntegrator):
    def __init__(self, props=mi.Properties()):
        super().__init__(props)
        self.max_depth = props.get('max_depth', -1)
        self.rr_depth = props.get('rr_depth', 3)
        self.hide_emitters = props.get('hide_emitters', False)
    def sample(self, scene, sampler, ray, medium, active):
        ray = mi.Ray3f(ray)
        L = mi.Spectrum(0)
        valid_ray = mi.Bool(False)
        return L , valid_ray, []

mi.register_integrator("some", lambda props: SomeSamplingIntegrator(props))
scene = mi.load_file('./scenes/cornell-box/cornell-box.xml')
integrator: SomeSamplingIntegrator = mi.load_dict(
        {
            "type": "some",
            "max_depth": 4,
        }
)
img = mi.render(scene, integrator=integrator, spp = 1)
mi.util.write_bitmap("./my_render.png", img)
 

It keep show the error:

2024-06-03 10:07:40 WARN  wrk0  [SamplingIntegrator] SamplingIntegrator Python implementations will have terrible performance in scalar_* modes. It is strongly recommended to switch to a cuda_* or llvm_* mode
2024-06-03 10:07:41 WARN  main  [SamplingIntegrator] SamplingIntegrator Python implementations will have terrible performance in scalar_* modes. It is strongly recommended to switch to a cuda_* or llvm_* mode
Traceback (most recent call last):
  File "C:\Users\Msi-laptop\source\mitsuba\ss-restir\test_heuristic_scalar3.py", line 25, in <module>
    img = mi.render(scene, integrator=integrator, spp = 1)
  File "C:\Users\Msi-laptop\anaconda3\envs\mitsuba\lib\site-packages\mitsuba\python\util.py", line 522, in render       
    return dr.custom(_RenderOp, scene, sensor, params, integrator,
  File "C:\Users\Msi-laptop\anaconda3\envs\mitsuba\lib\site-packages\drjit\router.py", line 5776, in custom
    output = inst.eval(**{ k: _dr.detach(v) for k, v in kwargs.items() })
  File "C:\Users\Msi-laptop\anaconda3\envs\mitsuba\lib\site-packages\mitsuba\python\util.py", line 377, in eval
    return self.integrator.render(
  File "C:\Users\Msi-laptop\source\mitsuba\ss-restir\test_heuristic_scalar3.py", line 12, in sample
    ray = mi.Ray3f(ray)
  File "C:\Users\Msi-laptop\anaconda3\envs\mitsuba\lib\site-packages\mitsuba\__init__.py", line 236, in __getattribute__    raise ImportError('Before importing any packages, you must '
ImportError: Before importing any packages, you must specify the desired variant of Mitsuba using "mitsuba.set_variant(..)".
The following variants are available: scalar_rgb, scalar_spectral, cuda_ad_rgb, llvm_ad_rgb.
You can also use the MI_DEFAULT_VARIANT environment variable to define a default variant.

However, the variant "cuda_ad_rgb" is working just fine.
Can you show me the point i was missing?
Big thanks to all the incredible contributors who have dedicated their time and expertise to this project.

[merlinND]

Hello @NhatMinh2208,

As discussed e.g. in #1093 (comment), custom Python plugins are not recommended in non-JIT variants because their performance would be terrible. I think because of this, they aren't tested and not guaranteed to work (please correct me if I'm wrong @njroussel).