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Make force fields support solid objects
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Description

Currently, if a force field is created with a Surface shape, particles (and hair and cloth) will be attracted or repelled along the normals of the mesh. With a positive force, particles are always repelled away from the nearest face. This works well for surface meshes, i.e. where the faces are two-sided. However, it is not useful for simulating solid meshes.

For a solid mesh, the faces should be considered to be single-sided: the direction of the force should not change when the particle crosses the face, as shown in B in the following diagram.

  • A: Current behaviour: force direction always reverses at face boundary and at midpoint between faces. Particles can get trapped inside solid objects.
  • B: Proposed behaviour: force direction is consistent across face boundary, but still reverses at midpoint. Allows particles to be repelled from surface and pushed out from inside.

This .blend file demonstrates the problem: if the particles or cloth end up inside the cube, they never escape. Under this proposal they should be repelled, because the force field strength is positive.

If this is option is implemented, it could be exposed as a new option, or the Both Z / +Z / -Z options could be reused for it.

Details

Type
Design

Event Timeline

Alex Fraser (z0r) added a project: BF Blender.
Alex Fraser (z0r) set Type to Design.
Alex Fraser (z0r) created this task.
Alex Fraser (z0r) raised the priority of this task from to Needs Triage by Developer.

Thanks for the graph. I understand better.
In fact, force field shape is relative to preset form (sphere,tube,cube).

It could be good to have options to make it also relative to force field shape in theses cases Surface or Every Point.

Sergey Sharybin (sergey) triaged this task as Normal priority.

@Lukas Toenne (lukastoenne), summoning here in order to have a look :)