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WIP: Mesh: Refactor vertex normals for determinism #105920

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Hans Goudey wants to merge 6 commits from HooglyBoogly:mesh-normals-calc-changes into main
pull from: HooglyBoogly:mesh-normals-calc-changes
merge into: blender:main

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Hans Goudey commented 2023-03-20 14:29:22 +01:00
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The current atomic additions in vertex normal calculation introduce
non-determinism because the order used when accumulating face
normals changes, influencing the results.

This causes bugs like #100250, where algorithms sensitive to small
changes in the values can have different results, causing renders
to be non-reproducible.

This PR fixes that by use a vertex to face topology map to
calculate each vertex's normals without atomics. When the
topology map is already available, this can be faster too, but
the topology map is expensive to create relative to the normal
calculation.

Goals:

  • Fix non-determinisitic results by avoiding floating point atomic operations
  • Avoid unnecessary recalculations by using SharedCache, allowed by splitting face and vertex normal calculation
  • Use cached mesh topology maps that can be used elsewhere too
  • Keep performance when caching can't be used close to or better than before

TODO:

  • Split out some changes to other commits/PRs
  • Optimize performance of topology map creation
The current atomic additions in vertex normal calculation introduce non-determinism because the order used when accumulating face normals changes, influencing the results. This causes bugs like #100250, where algorithms sensitive to small changes in the values can have different results, causing renders to be non-reproducible. This PR fixes that by use a vertex to face topology map to calculate each vertex's normals without atomics. When the topology map is already available, this can be faster too, but the topology map is expensive to create relative to the normal calculation. Goals: - Fix non-determinisitic results by avoiding floating point atomic operations - Avoid unnecessary recalculations by using `SharedCache`, allowed by splitting face and vertex normal calculation - Use cached mesh topology maps that can be used elsewhere too - Keep performance when caching can't be used close to or better than before TODO: - [ ] Split out some changes to other commits/PRs - [ ] Optimize performance of topology map creation
Hans Goudey changed title from WIP: Mesh: Refactor mesh normals for determinism and caching to WIP: Mesh: Refactor vertex normals for determinism and caching 2023-03-20 14:29:55 +01:00
Hans Goudey added this to the Modeling project 2023-03-20 14:30:02 +01:00
Hans Goudey force-pushed mesh-normals-calc-changes from 533a4b1f1c to 2c67540d89 2023-03-21 19:54:41 +01:00 Compare
Hans Goudey force-pushed mesh-normals-calc-changes from 2c67540d89 to 2f9b507095 2023-03-21 21:48:08 +01:00 Compare
Hans Goudey force-pushed mesh-normals-calc-changes from 2f9b507095 to 4757741152 2023-03-21 21:54:49 +01:00 Compare
Hans Goudey force-pushed mesh-normals-calc-changes from 4757741152 to 965e7b372e 2023-03-22 13:55:29 +01:00 Compare
Hans Goudey force-pushed mesh-normals-calc-changes from 965e7b372e to 594c407283 2023-03-22 16:44:33 +01:00 Compare
Hans Goudey force-pushed mesh-normals-calc-changes from 594c407283 to d7b51ce420 2023-03-22 17:02:05 +01:00 Compare
Hans Goudey force-pushed mesh-normals-calc-changes from d7b51ce420 to 4fc31afa67 2023-03-22 17:09:18 +01:00 Compare
Hans Goudey force-pushed mesh-normals-calc-changes from 4fc31afa67 to 11f7af424d 2023-03-22 17:21:45 +01:00 Compare
Hans Goudey commented 2023-03-22 17:27:34 +01:00
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The first timing information:

BEFORE
Timer 'vert_and_vert_normals': (Average: 47.3 ms, Min: 44.7 ms, Last: 47.8 ms)

AFTER
Timer 'poly_normals': (Average: 12.1 ms, Min: 11.8 ms, Last: 12.1 ms)
Timer 'Vert to corner offsets': (Average: 45.9 ms, Min: 43.2 ms, Last: 45.3 ms)
Timer 'Vert to poly indices': (Average: 89.2 ms, Min: 82.8 ms, Last: 89.3 ms)
Timer 'vert_normals': (Average: 164.0 ms, Min: 154.1 ms, Last: 162.0 ms)

On one hand this is bad news, since the topology map creation has to be much faster to give the same performance as before. On the other hand, just computing the vertex normals if the topology hasn't changed only takes 28ms, so if the topology hasn't changed, this can be faster than before by about 18%. That's nice for use cases like animation (at least when there's no subsurf).

The first timing information: ``` BEFORE Timer 'vert_and_vert_normals': (Average: 47.3 ms, Min: 44.7 ms, Last: 47.8 ms) AFTER Timer 'poly_normals': (Average: 12.1 ms, Min: 11.8 ms, Last: 12.1 ms) Timer 'Vert to corner offsets': (Average: 45.9 ms, Min: 43.2 ms, Last: 45.3 ms) Timer 'Vert to poly indices': (Average: 89.2 ms, Min: 82.8 ms, Last: 89.3 ms) Timer 'vert_normals': (Average: 164.0 ms, Min: 154.1 ms, Last: 162.0 ms) ``` On one hand this is bad news, since the topology map creation has to be much faster to give the same performance as before. On the other hand, just computing the vertex normals if the topology hasn't changed only takes 28ms, so if the topology hasn't changed, this can be faster than before by about 18%. That's nice for use cases like animation (at least when there's no subsurf).
Hans Goudey commented 2023-03-22 17:49:12 +01:00
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Though! The performance of the shared cache version (without the use of topology caches, just with split vert and poly normal calculation) is about the same as in main. So it would probably be nice to commit that first, and then consider determinism and topology caches next.

Though! The performance of the shared cache version (without the use of topology caches, just with split vert and poly normal calculation) is about the same as in `main`. So it would probably be nice to commit that first, and then consider determinism and topology caches next.
Hans Goudey force-pushed mesh-normals-calc-changes from 11f7af424d to 2cb74400ca 2023-03-22 23:27:33 +01:00 Compare
Hans Goudey force-pushed mesh-normals-calc-changes from 2cb74400ca to e000408dd9 2023-03-28 01:50:52 +02:00 Compare
Hans Goudey force-pushed mesh-normals-calc-changes from e000408dd9 to 02206aed5d 2023-04-03 18:22:05 +02:00 Compare
Hans Goudey force-pushed mesh-normals-calc-changes from 02206aed5d to 72c1bfaee3 2023-04-04 22:31:02 +02:00 Compare
Hans Goudey force-pushed mesh-normals-calc-changes from 72c1bfaee3 to 1ef44ebe9f 2023-04-10 23:23:02 +02:00 Compare
Hans Goudey force-pushed mesh-normals-calc-changes from 1ef44ebe9f to 9ceb145914 2023-05-01 00:17:14 +02:00 Compare
Hans Goudey changed title from WIP: Mesh: Refactor vertex normals for determinism and caching to WIP: Mesh: Refactor vertex normals for determinism 2023-08-20 02:51:28 +02:00
Hans Goudey closed this pull request 2023-08-31 00:54:57 +02:00
Hans Goudey deleted branch mesh-normals-calc-changes 2023-08-31 00:55:10 +02:00
Hans Goudey commented 2023-08-31 00:55:55 +02:00
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Superseded by #111718

Superseded by #111718

Pull request closed

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