Cycles Volumetric flickering when camera is inside volume #81258

Closed
opened 2020-09-28 17:35:13 +02:00 by Romain Toumi · 17 comments

System Information
Operating system: Windows 10
Graphics card: GTX Titan X (2016)

Blender Version
Broken: tested on 2.79 to 2.91
Worked: /

Cycles Volumetric flickering when camera is inside volume

exemple on my scene : (alpha channel, more visible)
Sequence_imbriquee_44.mp4

simple scene for test :
VOLUME_BUG.blend

  • it's a simple cube with a noise on a volume scatter shader (colorRamp + multiply for more visible bug)
  • camera animated to enter inside the mesh
  • render animation (after frame 15, when camera enter on the mesh, volumetric flickering.)

bug also in real volume (voxel) but less visible.

Result:
0001-0019.mp4

sorry for bad english.

**System Information** Operating system: Windows 10 Graphics card: GTX Titan X (2016) **Blender Version** Broken: tested on 2.79 to 2.91 Worked: / **Cycles Volumetric flickering when camera is inside volume** exemple on my scene : (alpha channel, more visible) [Sequence_imbriquee_44.mp4](https://archive.blender.org/developer/F8935536/Sequence_imbriquee_44.mp4) simple scene for test : [VOLUME_BUG.blend](https://archive.blender.org/developer/F8932174/VOLUME_BUG.blend) - it's a simple cube with a noise on a volume scatter shader (colorRamp + multiply for more visible bug) - camera animated to enter inside the mesh - render animation (after frame 15, when camera enter on the mesh, volumetric flickering.) bug also in real volume (voxel) but less visible. Result: [0001-0019.mp4](https://archive.blender.org/developer/F8982238/0001-0019.mp4) sorry for bad english.
Author

Added subscriber: @ToumiX

Added subscriber: @ToumiX
Romain Toumi changed title from Volumetric flickering when camera is inside volume (only mesh) to Cycles Volumetric flickering when camera is inside volume (only mesh) 2020-09-28 20:57:13 +02:00
Romain Toumi changed title from Cycles Volumetric flickering when camera is inside volume (only mesh) to Cycles Volumetric flickering when camera is inside volume 2020-09-28 22:07:54 +02:00

Added subscriber: @iss

Added subscriber: @iss

Changed status from 'Needs Triage' to: 'Needs User Info'

Changed status from 'Needs Triage' to: 'Needs User Info'

I can't reproduce this.
0001-0050.mp4

Can you update GPU drivers and check if this issue persists?

I can't reproduce this. [0001-0050.mp4](https://archive.blender.org/developer/F8961277/0001-0050.mp4) Can you update GPU drivers and check if this issue persists?
Author

i have try with a few drivers and OS,

GTX titan X (2016)
Studio driver 456.38 (windows 10)
Studio driver 452.06 (windows 10)
game ready driver 432.00 (24/07/19) (windows 10)

tried too with GTX 1070
Studio driver 452.06 (windows 10)
Studio driver 450.51.05 (on Linux Mint)

same results.

i have try with a few drivers and OS, GTX titan X (2016) Studio driver 456.38 (windows 10) Studio driver 452.06 (windows 10) game ready driver 432.00 (24/07/19) (windows 10) tried too with GTX 1070 Studio driver 452.06 (windows 10) Studio driver 450.51.05 (on Linux Mint) same results.

Added subscriber: @Alesk

Added subscriber: @Alesk

Here is the same scene rendered with 256 samples. The flickering is a lot more visible

volume_flickering.mp4

Here is the same scene rendered with 256 samples. The flickering is a lot more visible [volume_flickering.mp4](https://archive.blender.org/developer/F8979480/volume_flickering.mp4)
Author

same results with more step rate, with my final render settings for exemple :
for_report.mp4
it's subtle, but clearly visible

same results with more step rate, with my final render settings for exemple : [for_report.mp4](https://archive.blender.org/developer/F8980082/for_report.mp4) it's subtle, but clearly visible

Changed status from 'Needs User Info' to: 'Confirmed'

Changed status from 'Needs User Info' to: 'Confirmed'

Added subscriber: @Nubnubbud

Added subscriber: @Nubnubbud

could this be related to/the same bug I reported? they've both been in blender for quite some time, I feel it likely has the same or a related cause. Because the alpha channel makes it so much more noticeable, it probably has to do with some kind of uneven sample distribution, where rays are more likely to return a value right at the end of a step, or are less likely to right after one. This makes the volume react as if it had bands of density. Can you confirm if it is only happening when the camera is inside the volume for you?

The difference between our approaches appears to be that where ToumiX is using the camera to directly see the "density bands", I am using lights, and the rays get stopped in bands, leaving sparse, shaded areas in the volume. It's less flickering, and more pulsing... but given the pulses in both our experiences appear to move "toward" the camera, a fix for one could mean a fix for both,
0002.mp4

could this be related to/the same bug I reported? they've both been in blender for quite some time, I feel it likely has the same or a related cause. Because the alpha channel makes it so much more noticeable, it probably has to do with some kind of uneven sample distribution, where rays are more likely to return a value right at the end of a step, or are less likely to right after one. This makes the volume react as if it had bands of density. Can you confirm if it is only happening when the camera is inside the volume for you? The difference between our approaches appears to be that where ToumiX is using the camera to directly see the "density bands", I am using lights, and the rays get stopped in bands, leaving sparse, shaded areas in the volume. It's less flickering, and more pulsing... but given the pulses in both our experiences appear to move "toward" the camera, a fix for one could mean a fix for both, [0002.mp4](https://archive.blender.org/developer/F8991706/0002.mp4)

@Nubnubbud your bug looks very similar, but I can't open your file - got crash in GPU driver in 2.90 and 2.91. Also here bug seems to happen only when camera is already inside of volume object. Is this also issue in your case?

@Nubnubbud your bug looks very similar, but I can't open your file - got crash in GPU driver in 2.90 and 2.91. Also here bug seems to happen only when camera is already inside of volume object. Is this also issue in your case?

@iss here you go. The issue happens in both GPU and CPU, so you can use either. This just has the simulation frame I used for that animation packed in. Note how extreme I made the shader in order to make the issue visible without using an alpha mask. I checked your file, and when I used my shader on it, your issue, with the "flickering density" became my issue with the "pulsing shadows". I can only assume it looks like flickering because in your cases the clouds are so small, the "density gap" passes over them in only a frame or two. The smoke ball is about 1.5x the size of your entire cube, and I think it's related to raymarching nebtest290.blend

@iss here you go. The issue happens in both GPU and CPU, so you can use either. This just has the simulation frame I used for that animation packed in. Note how extreme I made the shader in order to make the issue visible without using an alpha mask. I checked your file, and when I used my shader on it, your issue, with the "flickering density" became my issue with the "pulsing shadows". I can only assume it looks like flickering because in your cases the clouds are so small, the "density gap" passes over them in only a frame or two. The smoke ball is about 1.5x the size of your entire cube, and I think it's related to raymarching [nebtest290.blend](https://archive.blender.org/developer/F8996814/nebtest290.blend)

@Nubnubbud

The vdb file is missing from your test file ;)

@Nubnubbud The vdb file is missing from your test file ;)

In #81258#1036055, @Alesk wrote:
@Nubnubbud

The vdb file is missing from your test file ;)

sorry!
after some confusion, then research I realized you can't pack .vdb files into blender files for sending. This is a zip file with the single frame of data it needs. oddly enough, when I "packed" the file, it bloated the blender file, even if it wasn't used...? nebtest290.7z

> In #81258#1036055, @Alesk wrote: > @Nubnubbud > > The vdb file is missing from your test file ;) sorry! after some confusion, then research I realized you can't pack .vdb files into blender files for sending. This is a zip file with the single frame of data it needs. oddly enough, when I "packed" the file, it bloated the blender file, even if it wasn't used...? [nebtest290.7z](https://archive.blender.org/developer/F9004662/nebtest290.7z)

This indeed looks like both reports are the same issue. So I will merge this into #56925

This indeed looks like both reports are the same issue. So I will merge this into #56925

Closed as duplicate of #56925

Closed as duplicate of #56925
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Reference: blender/blender#81258
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