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Extrude manifold creates non manifold geometry
Confirmed, NormalPublic

Description

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 451.77

Blender Version
Broken: version: 2.90.0, branch: master (modified), commit date: 2020-08-31 11:26, hash: rB0330d1af29c0
Worked: Probably never

Short description of error
I have not seen this in a list of known limitations therefore I am reporting this as a bug:

Extrude manifold tends to produce non manifold geometry if extrusion crosses an edge loop, which is in conflict of what the name of the tool suggest. One vertex connected to both closed and open edges in this way is not considered manifold geometry and also goes against common sense expectation of what kind of result this tool should provide.

Resulting geometry qualifies as non-manifold even according to Blender's own operator to select non-manifold geometry:

Exact steps for others to reproduce the error

  1. Create the geometry similar to the one one in the video (Cube with 2 subdivision)
  2. Select corner face on top of the cube and extrude it down past one or more edge loops, as seen in the video

Result: Resulting produced geometry is non-manifold:

Expected: The tool produces manifold geometry, as the name suggests.

Event Timeline

Philipp Oeser (lichtwerk) changed the task status from Needs Triage to Confirmed.Fri, Sep 4, 11:59 AM

Can confirm.

This was the thing where D5336 was really good at.
@Germano Cavalcante (mano-wii): do you think we can get the Extrude Manifold to match D5336 in that respect?

Don’t think it’s a bug... I think it’s a limitation. The https://developer.blender.org/D5336 was much more feature rich. I was hoping the current version was going to evolve into that: remove edges, faces and end is a must for this tool.