Alembic import. Normals are wrong where three edges meet while adaptive subdiv #49257

New Issue

Yegor · 2016-09-05T15:01:09+02:00

Yegor commented

2016-09-05 15:01:09 +02:00

System Information
CentOS, Nvidia Titan

Blender Version
Broken: 2.78 RC1

Short description of error
Adaptive subdiv gives wrong normals when three edges meet on imported alembic

Exact steps for others to reproduce the error
Import alembic.
Smooth with adaptive subdiv enabled.
Render the region where you have a vertex with three edges connected.

blender_adaptive_subdiv_faces_corners_bug.abc

blender_adaptive_subdiv_faces_corners_bug.blend

**System Information** CentOS, Nvidia Titan **Blender Version** Broken: 2.78 RC1 **Short description of error** Adaptive subdiv gives wrong normals when three edges meet on imported alembic **Exact steps for others to reproduce the error** Import alembic. Smooth with adaptive subdiv enabled. Render the region where you have a vertex with three edges connected. ![blender_adaptive_subdiv_faces_corners_bug.png](https://archive.blender.org/developer/F353560/blender_adaptive_subdiv_faces_corners_bug.png) [blender_adaptive_subdiv_faces_corners_bug.abc](https://archive.blender.org/developer/F353562/blender_adaptive_subdiv_faces_corners_bug.abc) [blender_adaptive_subdiv_faces_corners_bug.blend](https://archive.blender.org/developer/F353563/blender_adaptive_subdiv_faces_corners_bug.blend)

Yegor commented

2016-09-05 15:01:09 +02:00

Changed status to: 'Open'

Yegor commented

2016-09-05 15:01:09 +02:00

Added subscriber: @YegorSmirnov

Sergey Sharybin commented

2016-09-05 15:21:00 +02:00

Added subscriber: @Sergey

Kévin Dietrich was assigned by Sergey Sharybin

2016-09-05 15:21:00 +02:00

Sergey Sharybin commented

2016-09-05 15:21:01 +02:00

Kevin, mind having a look? :)

Kévin Dietrich removed their assignment 2016-09-05 18:10:32 +02:00

Mai Lavelle was assigned by Kévin Dietrich

2016-09-05 18:10:32 +02:00

Kévin Dietrich commented

2016-09-05 18:10:32 +02:00

Added subscriber: @kevindietrich

Kévin Dietrich commented

2016-09-05 18:10:32 +02:00

As far as I can tell, this doesn't have anything to do with Alembic. Normals are not read from Alembic archives, rather, they are generated on Blender's side based on how they are stored in the archive (either vertex/flat or face varying/smooth) ; this is because it is easier to recompute them than trying to figure out how other software store their normals and what to do with them. (In the future, with enough data, that might change.)

The problem still persists when removing the cache modifier and appears to be related to the dicing scale. By changing the dicing scale in the example file from 10.0 down to 1.0 the problem disappears. So, bouncing the report to Mai for investigation.

As far as I can tell, this doesn't have anything to do with Alembic. Normals are not read from Alembic archives, rather, they are generated on Blender's side based on how they are stored in the archive (either vertex/flat or face varying/smooth) ; this is because it is easier to recompute them than trying to figure out how other software store their normals and what to do with them. (In the future, with enough data, that might change.) The problem still persists when removing the cache modifier and appears to be related to the dicing scale. By changing the dicing scale in the example file from 10.0 down to 1.0 the problem disappears. So, bouncing the report to Mai for investigation.

Yegor commented

2016-09-05 18:42:09 +02:00

Yes, Kevin, it happens only on the imported object, not on the generated inside Blender. And on 1.0 it disappears visually, but it still there, obviously.

Mai Lavelle commented

2016-09-18 18:52:14 +02:00

Changed status from 'Open' to: 'Resolved'

Mai Lavelle closed this issue

2016-09-18 18:52:14 +02:00

Mai Lavelle commented

2016-09-18 18:52:14 +02:00

While the underlying issue is still there (precision loss for which there doesn't seem to be a clean solution) this should no longer be visible in renders due to 8f28441487.

While the underlying issue is still there (precision loss for which there doesn't seem to be a clean solution) this should no longer be visible in renders due to 8f28441487.

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Alembic import. Normals are wrong where three edges meet while adaptive subdiv #49257