Incorrect normals or tangents when using custom split normals #48986

New Issue

Trevor Harris · 2016-07-31T23:16:25+02:00

Trevor Harris commented

2016-07-31 23:16:25 +02:00

System Information
Operating system and graphics card
Windows 10
NVidia GTX 1080 Founder's Edition
Intel Core i7-4770K
32GB RAM

Blender Version
Broken: 2.77a

Short description of error
I noticed normal/tangent errors in a model file exported with a custom exporter I wrote for a game engine. After much investigation, these errors are reproducible within blender, which leads me to believe there is a problem with the normals/tangents that are generated from using calc_tangents(). Either that, or there is a problem with how auto_smooth uses the normals from the custom set, or the tangents are mismatched. I've narrowed it down as far as I can.
I'd made a post on the blenderartists forums, thinking it was a problem with my python script. You can look there for more details. https://blenderartists.org/forum/showthread.php?403787-Normals-not-being-read-correctly&p=3081617&viewfull=1#post3081617

Exact steps for others to reproduce the error
Based on a (as simple as possible) attached .blend file with minimum amount of steps
normals_bug.blend

Confirm normals appear to be correct in viewport. I've packed the baked normal map, but you may need to save it out before it will display properly in the viewport (another bug?).
Run the script in the text editor with the medal object selected.
Change the mesh's auto smooth setting off then back on to make it update itself.
Normal mapping no longer appears correct. When visually comparing the split normals, they appear identical to the correct normals, so either the visualization is incorrect, or the problem isn't with the normals but with the tangent vectors being used.

**System Information** Operating system and graphics card Windows 10 NVidia GTX 1080 Founder's Edition Intel Core i7-4770K 32GB RAM **Blender Version** Broken: 2.77a **Short description of error** I noticed normal/tangent errors in a model file exported with a custom exporter I wrote for a game engine. After much investigation, these errors are reproducible within blender, which leads me to believe there is a problem with the normals/tangents that are generated from using calc_tangents(). Either that, or there is a problem with how auto_smooth uses the normals from the custom set, or the tangents are mismatched. I've narrowed it down as far as I can. I'd made a post on the blenderartists forums, thinking it was a problem with my python script. You can look there for more details. https://blenderartists.org/forum/showthread.php?403787-Normals-not-being-read-correctly&p=3081617&viewfull=1#post3081617 **Exact steps for others to reproduce the error** Based on a (as simple as possible) attached .blend file with minimum amount of steps [normals_bug.blend](https://archive.blender.org/developer/F330681/normals_bug.blend) - Confirm normals appear to be correct in viewport. I've packed the baked normal map, but you may need to save it out before it will display properly in the viewport (another bug?). - Run the script in the text editor with the medal object selected. - Change the mesh's auto smooth setting off then back on to make it update itself. - Normal mapping no longer appears correct. When visually comparing the split normals, they appear identical to the correct normals, so either the visualization is incorrect, or the problem isn't with the normals but with the tangent vectors being used.

Trevor Harris commented

2016-07-31 23:16:25 +02:00

Changed status to: 'Open'

Trevor Harris commented

2016-07-31 23:16:25 +02:00

Added subscriber: @BeigeAlert

Bastien Montagne commented

2016-08-01 20:23:22 +02:00

Added subscriber: @mont29

Bastien Montagne self-assigned this 2016-08-01 20:23:22 +02:00

Bastien Montagne commented

2016-08-01 20:23:22 +02:00

First of all: PSD files cannot actually be loaded from packed files (they load from a filepath only, not from a chunk of memory, not sure why, probably some OIIO limitation…). Anyway, please avoid reporting several issues in same ticket, it’s harder to tackle.

As for normals and tangent space… My bet would be, re-setting custom normals generates some very small differences in some cases, which is in turn affecting tspace - will have a closer look about it though… :/

First of all: PSD files cannot actually be loaded from packed files (they load from a filepath only, not from a chunk of memory, not sure why, probably some OIIO limitation…). Anyway, please avoid reporting several issues in same ticket, it’s harder to tackle. As for normals and tangent space… My bet would be, re-setting custom normals generates some very small differences in some cases, which is in turn affecting tspace - will have a closer look about it though… :/

Bastien Montagne commented

2016-08-02 16:03:41 +02:00

OK, so can confirm that normals varies slightly (we are talking about forth decimal of vector components here…), actually they even varies between Edit and Object mode…

However, problem here was that re-setting custom normals was effectively splitting some normals, due to threashold detecting 'same' normals as being too low. Will increase it to a value that works here, and we'll see if it causes any issue otherwise (but doubt it will, new chosen value remains below 0.01°…).

OK, so can confirm that normals varies slightly (we are talking about forth decimal of vector components here…), actually they even varies between Edit and Object mode… However, problem here was that re-setting custom normals was effectively splitting some normals, due to threashold detecting 'same' normals as being too low. Will increase it to a value that works here, and we'll see if it causes any issue otherwise (but doubt it will, new chosen value remains below 0.01°…).

blender-admin commented

2016-08-02 16:05:20 +02:00

This issue was referenced by 2f5db2e45b

This issue was referenced by 2f5db2e45b7a8af51b15c45bb41f5dcb49ae9d4d

Bastien Montagne commented

2016-08-02 16:09:13 +02:00

Changed status from 'Open' to: 'Resolved'

Bastien Montagne closed this issue

2016-08-02 16:09:13 +02:00

Sign in to join this conversation.

No Label

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

Incorrect normals or tangents when using custom split normals #48986