Geo-Nodes Convex Hul stripey volume shading #90386

New Issue

HEYPictures · 2021-08-02T17:09:46+02:00

HEYPictures commented

2021-08-02 17:09:46 +02:00

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2060 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 471.41

Blender Version
Broken: version: 3.0.0 Alpha, branch: master, commit date: 2021-07-30 19:08, hash: 35894dc700
Worked: (newest version of Blender that worked as expected)

Short description of error
When you have Volume Shading on a Convex Hul object that you created in Geometry Nodes. Then it doesn't look right and flickery and stripey.

Exact steps for others to reproduce the error
Create a object, Not a plane, and create a convex hul in Geometry Nodes. Than shade it with volume.

Example in a Project:

Simple recreation:
2021-08-02 17-02-07.mp4
Convex Hul Volume Shading bug.blend

**System Information** Operating system: Windows-10-10.0.19041-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 2060 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 471.41 **Blender Version** Broken: version: 3.0.0 Alpha, branch: master, commit date: 2021-07-30 19:08, hash: `35894dc700` Worked: (newest version of Blender that worked as expected) **Short description of error** When you have Volume Shading on a Convex Hul object that you created in Geometry Nodes. Then it doesn't look right and flickery and stripey. **Exact steps for others to reproduce the error** Create a object, Not a plane, and create a convex hul in Geometry Nodes. Than shade it with volume. Example in a Project: ![Bug convex hul .png](https://archive.blender.org/developer/F10260250/Bug_convex_hul_.png) Simple recreation: [2021-08-02 17-02-07.mp4](https://archive.blender.org/developer/F10260230/2021-08-02_17-02-07.mp4) [Convex Hul Volume Shading bug.blend](https://archive.blender.org/developer/F10260259/Convex_Hul_Volume_Shading_bug.blend)

HEYPictures commented

2021-08-02 17:09:46 +02:00

Added subscriber: @Florian-10

Pratik Borhade commented

2021-08-03 07:15:07 +02:00

Added subscriber: @PratikPB2123

Richard Antalik commented

2021-08-04 01:38:54 +02:00

Added subscribers: @HooglyBoogly, @iss

Richard Antalik commented

2021-08-04 01:38:54 +02:00

I am not sure if this is bug, because this seems to be caused by overlapping faces between original geometry and hull. So you can add transform node with scale of 0.999999 to resolve this overlap.

Seems that this uses convex hull approximation from rigid body where such imprecision is acceptable? @HooglyBoogly would you consider small deviations like this to be a bug?

Also commit message says:

This commit adds a node to output the convex hull of any input geometry as a mesh, which is an enclosing geometry around a set of points.

So if this was fixed, you would probably want to scale hull down a bit anyway, since your picture seems to render outer faces as surface and inner as volume?

I am not sure if this is bug, because this seems to be caused by overlapping faces between original geometry and hull. So you can add transform node with scale of 0.999999 to resolve this overlap. Seems that this uses convex hull approximation from rigid body where such imprecision is acceptable? @HooglyBoogly would you consider small deviations like this to be a bug? Also commit message says: > This commit adds a node to output the convex hull of any input geometry as a mesh, which is an enclosing geometry around a set of points. So if this was fixed, you would probably want to scale hull down a bit anyway, since your picture seems to render outer faces as surface and inner as volume?

HEYPictures commented

2021-08-04 08:19:29 +02:00

I think it shouldn't interact with faces because it's Volume. That isn't realistic. I think that's, not the case the Convex hull is created for. For destroying the shading haha
When you scale up the shading is also kinda wired.2021-08-04 08-13-23.mp4

I think it shouldn't interact with faces because it's Volume. That isn't realistic. I think that's, not the case the Convex hull is created for. For destroying the shading haha When you scale up the shading is also kinda wired.[2021-08-04 08-13-23.mp4](https://archive.blender.org/developer/F10264253/2021-08-04_08-13-23.mp4)

Philipp Oeser commented

2021-08-04 10:31:43 +02:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2021-08-04 10:31:43 +02:00

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

Philipp Oeser closed this issue

2021-08-04 10:31:43 +02:00

Philipp Oeser commented

2021-08-04 10:31:43 +02:00

I think it shouldn't interact with faces because it's Volume. That isn't realistic. I think that's, not the case the Convex hull is created for. For destroying the shading haha

This has nothing to do with the Convex Hull I think. If you dont join it with the original mesh, shading is fine.
So, like @iss said, we are left with a mesh with overlapping faces. And even though it is shaded as volume, faces make a difference (since faces determine if a volume is entered/exited etc.).
If the difference is big enough (e.g. by introducing the 0.999 scaling like @iss suggested) renderer finds two intersections and thinks it is entering a second volume (darker), but with overlapping faces this might "fail" and sometimes two intersections are found, sometimes only one (brighter).

Dont think this can be considered a bug, will close.
(but of course feel free to comment again if issues persist or if this is a misunderstanding)

> I think it shouldn't interact with faces because it's Volume. That isn't realistic. I think that's, not the case the Convex hull is created for. For destroying the shading haha This has nothing to do with the Convex Hull I think. If you dont join it with the original mesh, shading is fine. So, like @iss said, we are left with a mesh with overlapping faces. And even though it is shaded as volume, faces **make a difference** (since faces determine if a volume is entered/exited etc.). If the difference is big enough (e.g. by introducing the 0.999 scaling like @iss suggested) renderer finds two intersections and thinks it is entering a second volume (darker), but with overlapping faces this might "fail" and sometimes two intersections are found, sometimes only one (brighter). Dont think this can be considered a bug, will close. (but of course feel free to comment again if issues persist or if this is a misunderstanding)

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Geo-Nodes Convex Hul stripey volume shading #90386