Normal Edit modifier incorrectly causes faces to become 'back faces' #55470

New Issue

Bart Heijltjes · 2018-06-13T15:37:25+02:00

Bart Heijltjes commented

2018-06-13 15:37:25 +02:00

System Information
Operating system and graphics card
N/A

Blender Version
Broken: 2.79b f4dc9f9
Worked: 2.73

Short description of error
In previous versions of Blender (tested 2.73) when adding a normal edit modifier, this would affect vertex normals but not face normals. In 2.79 the face normals are affected and faces are being culled.
I need the old behaviour for a non-realistic cell-shaded look. Lighting should be affected by the vertex normals, but obviously faces should not turn invisible just because the normals have been twisted. The erroneous behaviour persists when exporting to FBX and bringing the model into Unity.

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

Open attached .Blend file.
Inspect the Icosphere and notice that a number of its faces are being culled.
Move the 'PointNormalsAt' transform around to see both lighting and face culling change.
Select the Icosphere and turn the Edit Normals modifier off to see the full icosphere with faces outward as they should be.

normaleditbug.blend

**System Information** Operating system and graphics card N/A **Blender Version** Broken: 2.79b f4dc9f9 Worked: 2.73 **Short description of error** In previous versions of Blender (tested 2.73) when adding a normal edit modifier, this would affect vertex normals but not face normals. In 2.79 the face normals are affected and faces are being culled. I need the old behaviour for a non-realistic cell-shaded look. Lighting should be affected by the vertex normals, but obviously faces should not turn invisible just because the normals have been twisted. The erroneous behaviour persists when exporting to FBX and bringing the model into Unity. **Exact steps for others to reproduce the error** Based on a (as simple as possible) attached .blend file with minimum amount of steps - Open attached .Blend file. - Inspect the Icosphere and notice that a number of its faces are being culled. - Move the 'PointNormalsAt' transform around to see both lighting and face culling change. - Select the Icosphere and turn the Edit Normals modifier off to see the full icosphere with faces outward as they should be. [normaleditbug.blend](https://archive.blender.org/developer/F3683870/normaleditbug.blend)

Bart Heijltjes commented

2018-06-13 15:37:26 +02:00

Added subscriber: @WispBart

Philipp Oeser commented

2018-06-14 10:40:08 +02:00

Added subscribers: @mont29, @lichtwerk

Philipp Oeser commented

2018-06-14 10:40:08 +02:00

changed between 2.77a and 2.78
e3841c91f9, f08018f928, #42526

Imho current behaviour seems actually more correct (for most scenarios... but as you say: there might be other cases where poly flipping is undesired...)

Also not sure what NPR look exactly you are after, there might be solutions on the Unity side of things?

Turn off culling in Unity shader? (for npr this might be enough?)
somthing like this ?

@mont29: or should we make this [polygons_check_flip] an option in the modifier?

changed between 2.77a and 2.78 e3841c91f9, f08018f928, #42526 Imho current behaviour seems actually more correct (for most scenarios... but as you say: there might be other cases where poly flipping is undesired...) Also not sure what NPR look exactly you are after, there might be solutions on the Unity side of things? - Turn off culling in Unity shader? (for npr this might be enough?) - somthing like [this ](https://forum.unity.com/threads/double-sided-rendering-without-special-shaders.197923/)? @mont29: or should we make this [`polygons_check_flip`] an option in the modifier?

Bastien Montagne was assigned by Philipp Oeser

2018-06-14 10:41:32 +02:00

blender-admin commented

2018-06-14 11:41:12 +02:00

This issue was referenced by 0eb3246713

This issue was referenced by 0eb32467131543f224a222f0caf42df4ff9d7d65

Bastien Montagne commented

2018-06-14 11:45:03 +02:00

Changed status from 'Open' to: 'Resolved'

Bastien Montagne closed this issue

2018-06-14 11:45:03 +02:00

Bastien Montagne commented

2018-06-14 11:45:51 +02:00

Am not happy with re-introducing such buggy behavior, but on the other hand there is not other way I can think of to get same effect, and NPR often relies on buggy/incorrect behaviors anyway, so...

Bart Heijltjes commented

2018-06-14 17:24:10 +02:00

Thanks for the fix!

The look we're going for is flat-shaded characters with hard shadow lines (see Guilty Gear xrd for an example). Turning off backfaces could cause problems down the road, since these are logically just front facing tri's. We just want more control over how much light they are receiving.

Thanks for the fix! The look we're going for is flat-shaded characters with hard shadow lines (see Guilty Gear xrd for an example). Turning off backfaces could cause problems down the road, since these are logically just front facing tri's. We just want more control over how much light they are receiving.

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Reference: blender/blender#55470

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Normal Edit modifier incorrectly causes faces to become 'back faces' #55470