[Bug] drjit error when using batch of radiancemeters + llvm

[nestor98]

Summary

When using a batch sensor containing radiancemeters, drjit throws an exception in llvm_spectral and llvm_ad_spectral. This doesn't happen if I use the scalar_spectral variant, or if I use perspective sensors instead of radiancemeters. The error is:

Caught a critical exception: drjit::detail::collect_indices(): encountered an uninitialized function argument while recording a virtual function call!

System configuration

System information:

OS: Windows-11
CPU: Intel64 Family 6 Model 151 Stepping 2, GenuineIntel
GPU: NVIDIA GeForce GTX 1660 SUPER
Python: 3.12.0 (tags/v3.12.0:0fb18b0, Oct 2 2023, 13:03:39) [MSC v.1935 64 bit (AMD64)]
NVidia driver: 536.25
CUDA: 12.2.91
LLVM: 16.0.0

Dr.Jit: 0.4.6 (DEBUG)
Mitsuba: 3.5.2 (DEBUG)
Is custom build? False
Compiled with: MSVC 19.37.32822.0
Variants:
scalar_rgb
llvm_mono
scalar_spectral
llvm_ad_spectral
llvm_spectral

Description

I have narrowed down the scene to a minimal example with a single radiancemeter in the batch sensor. This error also does not happen when using a perspective sensor. The error

Caught a critical exception: drjit::detail::collect_indices(): encountered an uninitialized function argument while recording a virtual function call!

seems to happen by the end of the sample_ray_differential function in batch.cpp, just after calling the radiancemeter sample:

        auto [ray, spec] = sensor->sample_ray_differential(
            time, wavelength_sample, position_sample_2, aperture_sample,
            active);

Which is strange since it seems to finish executing the radiancemeter->sample_ray_differential function.

It may be some misconfiguration on my part, thanks for any help!

Steps to reproduce

This radiancemeter.xml scene will throw the error when executing mitsuba -m llvm_ad_spectral radiancemeter.xml or mitsuba -m llvm_spectral radiancemeter.xml:

<scene version="2.1.0">

<!-- Defaults, these can be set via the command line: -Darg=value -->

	<default name="resx" value="1"/>
	<default name="resy" value="1"/>

<!-- Camera and Rendering Parameters -->

	<integrator type="path" id="integrator" name="integrator">
		<integer name="max_depth" value="-1"/>
		<integer name="rr_depth" value="5000"/>
	</integrator>
	
	<!-- OPTION 1: -->
	<!-- Caught a critical exception: drjit::detail::collect_indices(): encountered an uninitialized function argument while recording a virtual function call!   -->
	<sensor type="batch" id="sensor" name="sensor">
		<film type="hdrfilm">
			<string name="pixel_format" value="rgba"/>
			<integer name="width" value="$resx"/>
			<integer name="height" value="$resy"/>
		</film>
		<sensor type="radiancemeter" name="sensor_0000">
			<transform name="to_world">
				<rotate x="1" angle="89.999995674289"/>
				<rotate z="1" angle="180.00000500895632"/>
				<translate value="0.000000 -0.100000 0.000000"/>
			</transform>
			<film type="hdrfilm">
				<string name="pixel_format" value="rgba"/>
				<integer name="width" value="$resx"/>
				<integer name="height" value="$resy"/>
			</film>
		</sensor>
	</sensor>
<!-- Materials -->


<!-- Emitters -->

	<shape type="rectangle" id="emitter" name="emitter">
		<transform name="to_world">
			<matrix value="10000.000000 0.000000 0.000000 0.000000 0.000000 0.000000 -10000.000000 0.000000 0.000000 10000.000000 0.000000 0.000000 0.000000 0.000000 0.000000 1.000000"/>
		</transform>
		<emitter type="area" name="emitter">
			<spectrum value="1000.000000" name="radiance"/>
		</emitter>
	</shape>

<!-- Shapes -->


<!-- Volumes -->

</scene>

Alternatives that do work

• Executing the above scene with a scalar version: mitsuba -m scalar_spectral radiancemeter.xml
• Using the same scene, but replacing the batch sensor with the inner radiancemeter:

<sensor type="radiancemeter" name="sensor_0000">
  <transform name="to_world">
	  <rotate x="1" angle="89.999995674289"/>
	  <rotate z="1" angle="180.00000500895632"/>
	  <translate value="0.000000 -0.100000 0.000000"/>
  </transform>
	<film type="hdrfilm">
		<string name="pixel_format" value="rgba"/>
		<integer name="width" value="$resx"/>
		<integer name="height" value="$resy"/>
	</film>
</sensor>

• Same scene, just replacing the inner radiancemeter with a perspective sensor:

<sensor type="batch" id="sensor" name="sensor">
	<film type="hdrfilm">
		<string name="pixel_format" value="rgba"/>
		<integer name="width" value="$resx"/>
		<integer name="height" value="$resy"/>
	</film>
      <sensor type="perspective" name="sensor_0000">
	      <transform name="to_world">
		      <rotate x="1" angle="89.999995674289"/>
		      <rotate z="1" angle="180.00000500895632"/>
		      <translate value="0.000000 -0.100000 0.000000"/>
	      </transform>
	      <film type="hdrfilm">
		      <string name="pixel_format" value="rgba"/>
		      <integer name="width" value="$resx"/>
		      <integer name="height" value="$resy"/>
	      </film>
      </sensor>
</sensor>

[arwk]

Hello,

Were you able to find the underlying problem? Today I ran into the same problem, but in my case with the CUDA backend.
I was trying to put multiple "radiencemeter" sensors into a "batch" sensor group to get them rendered efficiently.

Kind regards
arwk

[nestor98]

Hi @arwk, unfortunately I didn't manage to solve it. I didn't look into it very in depth after I realized the huge changes that are going on right now in drjit, as they could possibly remove the issue in the near future.

In the meantime, I just render the radiancemeters in a loop, which is quite slower but at least it works.

Best
Nestor

[njroussel]

Hi @nestor98

Sorry, I've somehow missed this entirely.

I'll try this out on the new upcoming Dr.JIT and report back :)

[arwk]

Hi @nestor98

Just wanted to share the workaround we came up with, which seems to work quite well.
We are using an orthographic camera with a 1x1 pixel film, heavily scaled down to be almost point-like.
This seems to approximate a radiencemeter quite well.

The following code defines such a sensor that is compatible with the batch-sensor-plugin

    "approximated-radiencemeter": {
        "type": "orthographic",
        "to_world": mi.ScalarTransform4f.look_at(
            origin=[0,0,3], target=[0, 0, 0], up=[0, 1, 0]
        ) @ mi.ScalarTransform4f.scale([.00001, .00001, 1]),
        # Scale the 1x1 Pixel down, to mimic the radiencemeter
        "film": {
            "type": "hdrfilm",
            "width": 1,
            "height": 1,
            "rfilter": {"type": "box"},
        },
    }