Subdivide with smoothness not symmetrical (not deterministic, depends of order of vertices in face) #79689

New Issue

Kruemel · 2020-08-10T13:55:18+02:00

Kruemel commented

2020-08-10 13:55:18 +02:00

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GT 430/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 388.13

Blender Version
Broken: version: 2.83.4, branch: master, commit date: 2020-08-05 06:00, hash: c113af8288
Worked: Never (2.8+)

Short description of error
Mesh is no longer centered along axis after using Subdivide with Smoothness greater zero. Projection of mesh is not exactly rectangular when looking form top.
The position of vertices, created with Subdivide with applied Smoothness, is wrong/arbitrary only if the vertex is placed inside the original face/polygon not along the edges of it. (Quads have one vertex inside face after one subdivision, Triangles need atleast two subdivisions for the error to appear because first subdivision creates new vertices only on edges)

Exact steps for others to reproduce the error
First example:

Open subdivide_smoothness_plane.blend
Apply Subdivide with Smoothness to the mesh
Mesh is no longer centered along y-Axis. Compare position of vertices created inside the two quads.
subdivide_smoothness_plane.blend

Second example:

Open subdivide_smoothness_multiple.blend
Apply Subdivide with Smoothness to the mesh with MORE then one Number of Cuts
Mesh is no longer centered along y-Axis
subdivide_smoothness_multiple.blend

**System Information** Operating system: Windows-10-10.0.18362-SP0 64 Bits Graphics card: GeForce GT 430/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 388.13 **Blender Version** Broken: version: 2.83.4, branch: master, commit date: 2020-08-05 06:00, hash: `c113af8288` Worked: Never (2.8+) **Short description of error** Mesh is no longer centered along axis after using Subdivide with Smoothness greater zero. Projection of mesh is not exactly rectangular when looking form top. The position of vertices, created with Subdivide with applied Smoothness, is wrong/arbitrary only if the vertex is placed inside the original face/polygon not along the edges of it. (Quads have one vertex inside face after one subdivision, Triangles need atleast two subdivisions for the error to appear because first subdivision creates new vertices only on edges) **Exact steps for others to reproduce the error** First example: 1. Open subdivide_smoothness_plane.blend 2. Apply Subdivide with Smoothness to the mesh 3. Mesh is no longer centered along y-Axis. Compare position of vertices created inside the two quads. [subdivide_smoothness_plane.blend](https://archive.blender.org/developer/F8765807/subdivide_smoothness_plane.blend) Second example: 1. Open subdivide_smoothness_multiple.blend 2. Apply Subdivide with Smoothness to the mesh with MORE then one Number of Cuts 3. Mesh is no longer centered along y-Axis [subdivide_smoothness_multiple.blend](https://archive.blender.org/developer/F8765818/subdivide_smoothness_multiple.blend)

Kruemel commented

2020-08-10 13:55:18 +02:00

Added subscriber: @Kruemel

Richard Antalik commented

2020-08-11 13:28:31 +02:00

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

Campbell Barton commented

2020-09-22 03:28:12 +02:00

Added subscriber: @ideasman42

Campbell Barton commented

2020-09-22 03:28:12 +02:00

The problem looks to be caused by the method used to calculate smoothness. It's only ever calculated along a single edge, this means a vertex in the center of a quad (for example) may be positioned based on only two of the opposite edges on the side of the quad, the edges picked depend on the order in the face, giving non-symmetrical results.

A short term fix could be to order quads based on edge-length, so matching quads at least use matching results.

See P1646, although it's much better, the results are still not completely symmetrical.

To fix this we'll probably need to change the calculation to take all original surrounding vertices into account when calculating the smooth position.

Since this is a fairly large change, marking as a known-issue as I'm not sure when this might be resolved.

The problem looks to be caused by the method used to calculate smoothness. It's only ever calculated along a single edge, this means a vertex in the center of a quad (for example) may be positioned based on only two of the opposite edges on the side of the quad, the edges picked depend on the order in the face, giving non-symmetrical results. A short term fix could be to order quads based on edge-length, so matching quads at least use matching results. See [P1646](https://archive.blender.org/developer/P1646.txt), although it's much better, the results are still not completely symmetrical. To fix this we'll probably need to change the calculation to take all original surrounding vertices into account when calculating the smooth position. Since this is a fairly large change, marking as a known-issue as I'm not sure when this might be resolved.

Campbell Barton changed title from ~~Subdivide with Smoothness not symmetric~~ to Subdivide with smoothness not symmetrical (not deterministic, depends of order of vertices in face)

2020-09-22 03:52:11 +02:00

Philipp Oeser removed the

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Subdivide with smoothness not symmetrical (not deterministic, depends of order of vertices in face) #79689