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Maniphest T84779

Geonode Modifier outputting black vertex color
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Description

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce RTX 2080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 452.06

Blender Version
Broken: version: 2.92.0 Alpha, branch: master, commit date: 2021-01-12 20:03, hash: rB719bea0d6d06

Short description of error
When filling a new attr with Vector/Bool/Color type named with the same name of a vertex-color and a vertex-group, vertex-color rendering will be black when in vertex-paint mode within the openGL viewport


expected behavior:

  • geonode could write a vertex-color attr. If it can write vg's, there's no logical reasons it shouldn't be able to write a vcol, isn't it? It would make sense depending on the attr type, Boolean/Float can only be vg and Vector/Color type could only be vcol.
    • for example:
      • user choose to fill a new attr with bool or float type -> if vg with same name of the attr found, the vg would fill automatically with the attr values (current behavior)
      • user choose to fill a new attr with Vector/Color type -> if vcol with same name of the attr found, the vcol would fill automatically RGB depending on given vectors
  • OR geonode completely ignore vertex color, thus vcol shouldn't go black in viewport (only for now I suppose? i hope attr to vcol will be supported later)

Exact steps for others to reproduce the error

  1. create a subdivided plane
  2. add a new vg called "Col"
  3. add a new vcol called "Col" and draw something
  4. create a new geonode modifier, fill a new attr with an attribute fill node, choose an attr named "Col", if choosing filling with type Vector/Color/Bool/
  5. go in vertex-color mode, it will render everything in black

File available below

attr_affecting_vcol.blend6 MBDownload

Event Timeline

NoobiePoopsie (helloidonthaveanyideaformyusername) created this task.Jan 16 2021, 2:07 PM
NoobiePoopsie (helloidonthaveanyideaformyusername) added a project: Geometry Nodes.
NoobiePoopsie (helloidonthaveanyideaformyusername) updated the task description. (Show Details)Jan 16 2021, 2:20 PM
NoobiePoopsie (helloidonthaveanyideaformyusername) updated the task description. (Show Details)
Jacques Lucke (JacquesLucke) closed this task as Archived.Jan 16 2021, 3:47 PM
Jacques Lucke (JacquesLucke) added a subscriber: Jacques Lucke (JacquesLucke).

This is not a bug, even though I understand the confusion.

The issue is that the Attribute Fill node deletes the existing attribute (which is a vertex group internally) and creates a new attribute with the new type (they cannot exist at the same time due to a name conflict). This new attribute won't be a vertex group internally (no new attribute will be created as vertex group currently). The vertex weight edit mode cannot display the group, because it does not exist on the evaluated mesh. It might be possible to display the original vertex group without edits in the viewport somehow.

The fundamental issue is that Blender had very specialized attribute types (vertex groups, vertex colors, etc.) and now we are slowly moving towards a more generic attribute system that allows various attribute types (integer, float, color, ...) on various domains (vertex, corner, edge, ...). The viewport cannot draw these more generic attributes yet. For the future we have planned an Attribute Edit Mode that can edit all the different kinds of attributes.

In general you can't rely on the fact that vertex group that is used by geometry nodes, will come out as vertex group as well. It might be converted to the "new" system implicitly. Hence you see black.

I think the situation will improve once more parts of Blender are aware of the more generic attribute system. This will not be implemented as a bug fix but as general feature development, therefore I'm closing this.