Curve to Mesh node causes other objects to edge split when not shaded smooth #92886

New Issue

Erindale · 2021-11-06T19:24:45+01:00

Erindale commented

2021-11-06 19:24:45 +01:00

System Information
Operating system: Windows-10-10.0.22000-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2070 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 472.39

Blender Version
Broken: version: 3.0.0 Beta, branch: master, commit date: 2021-11-05 22:17, hash: 7a5b8cb202
Worked: (newest version of Blender that worked as expected)

Short description of error
When using a Curve to Mesh node, it causes other objects joined to it to be read with each face as a separate mesh island by Cycles (using the Random per Island socket of the Geometry node in shaders). This only happens while using Flat shading AND the Curve to Mesh is plugging into the first position of the Join Geometry node. In any other order it will not happen.
Also happens with more mesh objects as long as the Curve to Mesh object is the first on in the Join node.

The edges aren't actually split, it just seems to be Cycles that thinks they're individual mesh islands.

Exact steps for others to reproduce the error
Add a grid node and join it to a curve going through a Curve to Mesh node.
Ensure the Curve to Mesh is the first connection into the Join Geo node.
Assign a material to the grid and in the shader, view the Random Per Island output of the Geometry node.

2021-11-06 18-08-29.mp4

Mesh Island Bug.blend

**System Information** Operating system: Windows-10-10.0.22000-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 2070 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 472.39 **Blender Version** Broken: version: 3.0.0 Beta, branch: master, commit date: 2021-11-05 22:17, hash: `7a5b8cb202` Worked: (newest version of Blender that worked as expected) **Short description of error** When using a Curve to Mesh node, it causes other objects joined to it to be read with each face as a separate mesh island by Cycles (using the Random per Island socket of the Geometry node in shaders). This only happens while using Flat shading AND the Curve to Mesh is plugging into the first position of the Join Geometry node. In any other order it will not happen. Also happens with more mesh objects as long as the Curve to Mesh object is the first on in the Join node. The edges aren't actually split, it just seems to be Cycles that thinks they're individual mesh islands. **Exact steps for others to reproduce the error** Add a grid node and join it to a curve going through a Curve to Mesh node. Ensure the Curve to Mesh is the first connection into the Join Geo node. Assign a material to the grid and in the shader, view the Random Per Island output of the Geometry node. [2021-11-06 18-08-29.mp4](https://archive.blender.org/developer/F11752369/2021-11-06_18-08-29.mp4) [Mesh Island Bug.blend](https://archive.blender.org/developer/F11752403/Mesh_Island_Bug.blend)

Erindale commented

2021-11-06 19:24:45 +01:00

Added subscriber: @Erindale

blender-admin commented

2021-11-06 19:24:45 +01:00

#95619 was marked as duplicate of this issue

blender-admin commented

2021-11-06 19:24:45 +01:00

#94258 was marked as duplicate of this issue

Mattias Fredriksson commented

2021-11-06 23:32:05 +01:00

Added subscriber: @Osares

Mattias Fredriksson commented

2021-11-06 23:32:05 +01:00

Can confirm this is an issue of inconsistency but it is not straight forward if it can be classified as a bug or not as the issue originates from 'auto smooth' flag being enabled in 'Curve to Mesh' node. The same outcome can be achieved on a subdivided plane by enabling the 'auto smooth' setting with flat shading.

The issue(s) to geometry nodes is:

ME_AUTOSMOOTH flag is set in 'blender/source/blender/blenkernel/intern/curve_to_mesh_convert.cc' on row 719.
Only flags from the first mesh instance are copied to the output mesh in the 'Join Geometry' node (which is the reason for the outcome to be order dependent).
ME_AUTOSMOOTH flag is not transferred when applying the geometry modifier.

I am not 100% certain to why auto smooth is enabled or if it changes the result if the mesh is not in 'smooth shading' mode. I'm neither certain what 'auto smooth' achieves when the angel is set to 180* as in 'curve_to_mesh_convert.cc' we have:

719: mesh->flag |= ME_AUTOSMOOTH;
720: mesh->smoothresh = DEG2RADF(180.0f);

To me it looks off and removing/commenting the first of the two lines resolves the issue, but I can't discern if that is a viable solution to this issue.

In the image the plane circled in blue is a subdivided plane mesh with flat shading and Object Data Properties>Normals>Auto Smooth enabled.

BR

Can confirm this is an issue of inconsistency but it is not straight forward if it can be classified as a bug or not as the issue originates from 'auto smooth' flag being enabled in 'Curve to Mesh' node. The same outcome can be achieved on a subdivided plane by enabling the 'auto smooth' setting with flat shading. The issue(s) to geometry nodes is: 1. ME_AUTOSMOOTH flag is set in 'blender/source/blender/blenkernel/intern/curve_to_mesh_convert.cc' on row 719. 2. Only flags from the first mesh instance are copied to the output mesh in the 'Join Geometry' node (which is the reason for the outcome to be order dependent). 3. ME_AUTOSMOOTH flag is not transferred when applying the geometry modifier. I am not 100% certain to why auto smooth is enabled or if it changes the result if the mesh is not in 'smooth shading' mode. I'm neither certain what 'auto smooth' achieves when the angel is set to 180* as in 'curve_to_mesh_convert.cc' we have: 719: mesh->flag |= ME_AUTOSMOOTH; 720: mesh->smoothresh = DEG2RADF(180.0f); To me it looks off and removing/commenting the first of the two lines resolves the issue, but I can't discern if that is a viable solution to this issue. ![Screenshot (74).png](https://archive.blender.org/developer/F11753544/Screenshot__74_.png) In the image the plane circled in blue is a subdivided plane mesh with flat shading and Object Data Properties>Normals>Auto Smooth enabled. BR

Erik Abrahamsson commented

2021-11-07 00:01:09 +01:00

Added subscriber: @erik85

Erik Abrahamsson commented

2021-11-07 00:01:09 +01:00

In my patch D12080 (Auto Smooth node) I transfer the flags and smoothresh when the mesh is applied.. Maybe atleast that would be an improvement.

In my patch [D12080](https://archive.blender.org/developer/D12080) (Auto Smooth node) I transfer the flags and smoothresh when the mesh is applied.. Maybe atleast that would be an improvement.

Mattias Fredriksson commented

2021-11-07 01:12:08 +01:00

It would at least help, but it does not resolve the inconsistencies that occur here as it would just be another way for multiple values to exist at the same time within the node graph while only a single value can exist in the output (with the modifier applied or otherwise). Finding a general solution to this would probably require defining how these mesh/object-wide flags should be handled as the final outcome in these scenarios will always appear arbitrary for most users?

Cheers

It would at least help, but it does not resolve the inconsistencies that occur here as it would just be another way for multiple values to exist at the same time within the node graph while only a single value can exist in the output (with the modifier applied or otherwise). Finding a general solution to this would probably require defining how these mesh/object-wide flags should be handled as the final outcome in these scenarios will always appear arbitrary for most users? Cheers

Jacques Lucke commented

2021-11-19 11:01:57 +01:00

Added subscriber: @JacquesLucke

Jacques Lucke commented

2021-11-19 11:01:57 +01:00

Ref #93208.

Hans Goudey commented

2021-12-21 01:01:26 +01:00

Added subscriber: @Baardaap

Pratik Borhade commented

2022-01-21 07:02:10 +01:00

Added subscriber: @PratikPB2123

Pratik Borhade commented

2022-01-21 07:02:10 +01:00

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

Pratik Borhade commented

2022-01-21 07:02:10 +01:00

I think we can confirm this report due to inconsistencies.

(Feel free to revert the status)

I think we can confirm this report due to inconsistencies. (Feel free to revert the status)

Hans Goudey commented

2022-02-01 23:55:56 +01:00

Added subscriber: @HooglyBoogly

Hans Goudey commented

2022-02-01 23:55:56 +01:00

Unfortunately this is a consequence of the (bad in retrospect) decision to output the mesh from the curve to mesh node with the auto smooth flag set.

There may be ways to change this with versioning, but that would have to wait until we can get agreement on #93551 and start implementing those changes.

Unfortunately this is a consequence of the (bad in retrospect) decision to output the mesh from the curve to mesh node with the auto smooth flag set. There may be ways to change this with versioning, but that would have to wait until we can get agreement on #93551 and start implementing those changes.

Pratik Borhade commented

2022-02-09 03:54:43 +01:00

Added subscriber: @slowburn

Pratik Borhade commented

2022-02-09 04:02:46 +01:00

I've closed the other report as it looks identical: #95619
Can't we also add other modules to this report (#render_cycles ?)
Not sure if issue is related to Geometry nodes only

I've closed the other report as it looks identical: #95619 Can't we also add other modules to this report (#render_cycles ?) Not sure if issue is related to Geometry nodes only

slowburn commented

2022-02-09 22:17:56 +01:00

Yes, please add Cycles module. This is primarily an issue with Random per Island input and affects all meshes.
The fact that geometry nodes does something weird with smooth shading only makes the problem more visible, but it's not the cause. So it can't be fixed on GN side.

Yes, please add Cycles module. This is primarily an issue with Random per Island input and affects all meshes. The fact that geometry nodes does something weird with smooth shading only makes the problem more visible, but it's not the cause. So it can't be fixed on GN side.

Hans Goudey commented

2022-02-09 22:38:13 +01:00

While the result might be the same for both these reports, they are completely unrelated internally and shouldn't be merged. That report shouldn't be classified as a known issue just because this one is.

Philipp Oeser commented

2022-03-29 12:23:21 +02:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2022-03-29 12:23:21 +02:00

Note #72284 (Random Per Island working incorrectly with sharp edges and volumes) is related

Philipp Oeser removed the

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Curve to Mesh node causes other objects to edge split when not shaded smooth #92886