SoftBody3D editor gizmo does not highlight pinned points correctly

[simpkins]

Tested versions

• Reproducible in 4.5-beta1 and earlier versions

System information

Windows 11

Issue description

When editing a SoftBody3D, the editor gizmo shows handles at each mesh vertex. Clicking on one of these handles is supposed to pin the point, and then show it highlighted in blue. However, depending on the mesh it usually does not highlight the pinned vertices correctly.

The problem appears to be that the editor gizmo draws one handle per vertex in the rendered mesh, and not one handle per physics vertex. In most meshes, there are many render vertices at the same coordinates (just with different normals and UV coordinates from one another).

For instance, consider the following mesh:

This BoxMesh has 24 vertices: there are 3 vertices at each corner of the cube, since each face has a different normal. However, from a physics perspective the soft body only has 8 vertices that get simulated.

The editor is showing 24 separate handles here, and is displaying 3 separate handles on top of each other at each corner. When you click on a handle it attempts to render it in blue, but in practice one of the non-highlighted handles usually renders on top of it, so you can't tell that it is highlighted.

The soft body gizmo seems like it should be fixed to only display 8 handles in this case, so it can correctly display which handles should be highlighted. (In practice there are only 8 logical vertices that can be pinned; each physics vertex will be pinned if any one of the associated render vertices are pinned.)

Steps to reproduce

• Add a SoftBody3D to a scene
• Attach a BoxMesh to it
• Try clicking on some of the points to highlight it

In practice this will happen with many other mesh types as well. Imported ArrayMesh objects often have this problem.
The SphereMesh also has this problem at the ends of the sphere and along a seem down one segment of the sphere
The primitive PlaneMesh type is one of the few mesh types that does not have this problem, because it has a simple 1:1 mapping between render vertices and physics vertices.

Minimal reproduction project (MRP)

soft-body-pinned-points.zip

[Calinou]

What's the best way to fix this?

• When toggling a vertex, also toggle vertices at the same position.
• Only show a gizmo per actual vertex unique position in the first place. Toggling this gizmo will toggle vertices at the same position automaticvally.
  • This ensures we don't draw overlapping gizmos, which is faster. However, how do we ensure the mapping between the gizmos you see and what the PhysicsServer expects remains correct?

Both approaches will require looping through all vertices to determine unique positions, which could be slow for meshes with thousands of vertices or more.

[simpkins]

Personally I think the best fix is to only draw 1 gizmo per physics vertex, by having SoftBody3D keep track of the render vertex <-> physics vertex mapping.

Currently this mapping is done in the physics server, but I think it should be done in the SoftBody3D code instead, and we should only tell the physics server about the actual physics vertices, and not the full list of render vertices. This is inline with my suggestions in godotengine/godot-proposals#12670 for improving the PhysicsServer3D APIs.

In the short term this would require having 2 copies of this mapping, which is slightly unfortunate (adding a copy in SoftBody3D, in addition to the data tracked in the physics server). For this particular gizmo UI problem we could track this extra copy of the map only when running in the editor. However, having this vertex mapping available in SoftBody3D would also help with some other issues, like improving the shading behavior by moving render normal calculation into SoftBody3D (instead of having the physics servers doing this rendering logic).