Volume Displace blocky #81983

New Issue

Gurra · 2020-10-23T00:13:23+02:00

Gurra commented

2020-10-23 00:13:23 +02:00

System Information
Operating system: Windows 10
Graphics card: GTX 970

Blender Version
2.91 Beta

Short description of error
When using the Volume Displace you get weird blockyness when rendering in Cycles.
This is a suzanne turned into a volume with a displace turned to 0 (doesn't matter what value I use, still looks the same)

And this is with the modifier turned off

Exact steps for others to reproduce the error
Create monkey, create an empty volume, add a Mesh to Volume modifier (bump up the voxel amount higher for clearer effect of the bug), add a Volume Displace modifier, render in Cycles.
volbug.blend

**System Information** Operating system: Windows 10 Graphics card: GTX 970 **Blender Version** 2.91 Beta **Short description of error** When using the Volume Displace you get weird blockyness when rendering in Cycles. This is a suzanne turned into a volume with a displace turned to 0 (doesn't matter what value I use, still looks the same) ![voldispbug1.jpg](https://archive.blender.org/developer/F9038574/voldispbug1.jpg) And this is with the modifier turned off ![voldispbug2.jpg](https://archive.blender.org/developer/F9038599/voldispbug2.jpg) **Exact steps for others to reproduce the error** Create monkey, create an empty volume, add a Mesh to Volume modifier (bump up the voxel amount higher for clearer effect of the bug), add a Volume Displace modifier, render in Cycles. [volbug.blend](https://archive.blender.org/developer/F9038655/volbug.blend)

Gurra commented

2020-10-23 00:13:23 +02:00

Added subscriber: @Gurra

blender-admin commented

2020-10-23 00:13:23 +02:00

#82458 was marked as duplicate of this issue

Gurra changed title from ~~Volume Displace~~ to Volume Displace blocky

2020-10-23 00:13:46 +02:00

Richard Antalik commented

2020-10-23 21:03:23 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Jacques Lucke commented

2020-11-05 17:40:19 +01:00

Added subscriber: @JacquesLucke

Jacques Lucke commented

2020-11-05 17:40:19 +01:00

I think this happens for the following reasons.

The volume displace modifier prunes the resulting openvdb tree to reduce memory consumption. This might remove leaf nodes when all voxels in it have the same value. The logical voxel value does not change, because an internal node stores the value of all voxels.
Cycles generates a mesh on the boundary of a volume, presumably to speedup rendering. This mesh is generated incorrectly in the pruned tree.

This should really be solved before the release. I'm looking into it now.

I think this happens for the following reasons. 1. The volume displace modifier prunes the resulting openvdb tree to reduce memory consumption. This might remove leaf nodes when all voxels in it have the same value. The logical voxel value does not change, because an internal node stores the value of all voxels. 2. Cycles generates a mesh on the boundary of a volume, presumably to speedup rendering. This mesh is generated incorrectly in the pruned tree. This should really be solved before the release. I'm looking into it now.

Jacques Lucke commented

2020-11-05 18:06:03 +01:00

Added subscriber: @brecht

Jacques Lucke commented

2020-11-05 18:06:03 +01:00

This patch removes much of the optimization, but it solves the problem: P1754.
I won't finish a patch that still contains the optimization today.

This patch removes much of the optimization, but it solves the problem: [P1754](https://archive.blender.org/developer/P1754.txt). I won't finish a patch that still contains the optimization today.

Brecht Van Lommel commented

2020-11-05 18:20:33 +01:00

Just a guess, but maybe we are not handling tile values correctly?
https://www.openvdb.org/documentation/doxygen/overview.html#subsecValues

We iterate over leaf nodes, but I'm not sure what happens when internal nodes have a tile value for example.

Just a guess, but maybe we are not handling tile values correctly? https://www.openvdb.org/documentation/doxygen/overview.html#subsecValues We iterate over leaf nodes, but I'm not sure what happens when internal nodes have a tile value for example.

Jacques Lucke commented

2020-11-05 18:30:11 +01:00

Yes indeed, I'm pretty sure that is the issue here. We can actually see that the "inside" of the volume is rendered empty. The conversion to a dense matrix in cycles yields the same result (I checked adding up all the densities with and without modifier, and they are the same).

We just have to find a good and correct way to build the mesh taking into account internal nodes as well. It does not seem too hard, but I need to think about it a bit more.

2020-11-05 18-26-28.mp4

Yes indeed, I'm pretty sure that is the issue here. We can actually see that the "inside" of the volume is rendered empty. The conversion to a dense matrix in cycles yields the same result (I checked adding up all the densities with and without modifier, and they are the same). We just have to find a good and correct way to build the mesh taking into account internal nodes as well. It does not seem too hard, but I need to think about it a bit more. [2020-11-05 18-26-28.mp4](https://archive.blender.org/developer/F9210823/2020-11-05_18-26-28.mp4)

Brecht Van Lommel commented

2020-11-11 18:05:56 +01:00

Added subscribers: @FilipMond, @iss