Regression: Imported FBX has wrong vertex normals/sharp edges in 3.6 Beta #108170

New Issue

System Information
Operating system: Windows-10-10.0.19044-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 528.02

Blender Version
Broken: version: 3.6.0 Alpha, branch: main, commit date: 2023-05-12 23:03, hash: 654cfc06c591
Worked: version: 3.6.0 Alpha, branch: main, commit date: 2023-05-09 04:08, hash: c49a0fa474de

Short description of error
Imported FBX has wrong vertex normals. Same model imported with Blender 3.51 has correct shading.

Exact steps for others to reproduce the error

Created a cube with Shift + A/Mesh/Cube.
Export the cube as FBX with default export settings.
Import the FBX with default import settings and observe deformed shading and assigned sharp edges.

**System Information** Operating system: Windows-10-10.0.19044-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 3080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 528.02 **Blender Version** Broken: version: 3.6.0 Alpha, branch: main, commit date: 2023-05-12 23:03, hash: `654cfc06c591` Worked: version: 3.6.0 Alpha, branch: main, commit date: 2023-05-09 04:08, hash: `c49a0fa474de` **Short description of error** Imported FBX has wrong vertex normals. Same model imported with Blender 3.51 has correct shading. **Exact steps for others to reproduce the error** 1. Created a cube with Shift + A/Mesh/Cube. 2. Export the cube as FBX with default export settings. 3. Import the FBX with default import settings and observe deformed shading and assigned sharp edges.

3_6_normals_issue.jpg

57 KiB

default cube 4d0.fbx

11 KiB

I don't think anything changed in FBX code regarding custom normals, so would rather suspect some breakage of API during the Mesh refactors in the area?

We are missing reproducible case here though, please attach the FBX file.

We are missing reproducible case here though, please attach the FBX file.

The repro is not working? Here is the Cube.

> We are missing reproducible case here though, please attach the FBX file. The repro is not working? Here is the Cube.

cube.fbx

11 KiB

Mesh.normals_split_custom_set appears to not be setting sharp edges correctly. Cube primitive is pretty obvious, but for some it's not very noticeable, like Cone and Icosphere primitives.

I've made a script that should reproduce the issue (I don't quite have the exact Blender versions listed in the issue, only a slightly older 3.6.0a 2023-05-04 6b5b777ca3ea (no issue present) and a newer 3.6.0b 2023-05-18 0f67ac45471d (issue present)).

import bpy

# Run this script with an active mesh object

mesh = bpy.context.object.data

# Setup:
# Clear existing custom split normals
bpy.ops.mesh.customdata_custom_splitnormals_clear()
# No issue appears to occur where either sharp_face or sharp_edge are True.
# Removing the attributes has the same effect as all values being set to False.
if "sharp_edge" in mesh.attributes:
    for se in mesh.attributes["sharp_edge"].data:
        se.value = False
    # mesh.attributes.remove(mesh.attributes["sharp_edge"])
if "sharp_face" in mesh.attributes:
    for sf in mesh.attributes["sharp_face"].data:
        sf.value = False
    # mesh.attributes.remove(mesh.attributes["sharp_face"])

# Get loop normals
# Since we're calculating them rather than taking them from an imported FBX,
# mesh.auto_smooth_angle and mesh.use_auto_smooth affect the calculated split normals.
# Issues only appear to occur where the split normals create sharp edges.
# auto_smooth_angle of zero will ensure calculated split normals result in sharp edges.
mesh.auto_smooth_angle = 0
mesh.use_auto_smooth = True
mesh.calc_normals_split()
loop_normals = [l.normal for l in mesh.loops]

# Set loop normals
mesh.normals_split_custom_set(loop_normals)

The top meshes are duplicates of the below meshes that have then had the script run on them.

`Mesh.normals_split_custom_set` appears to not be setting sharp edges correctly. Cube primitive is pretty obvious, but for some it's not very noticeable, like Cone and Icosphere primitives. I've made a script that should reproduce the issue (I don't quite have the exact Blender versions listed in the issue, only a slightly older 3.6.0a 2023-05-04 `6b5b777ca3ea` (no issue present) and a newer 3.6.0b 2023-05-18 `0f67ac45471d` (issue present)). ```py import bpy # Run this script with an active mesh object mesh = bpy.context.object.data # Setup: # Clear existing custom split normals bpy.ops.mesh.customdata_custom_splitnormals_clear() # No issue appears to occur where either sharp_face or sharp_edge are True. # Removing the attributes has the same effect as all values being set to False. if "sharp_edge" in mesh.attributes: for se in mesh.attributes["sharp_edge"].data: se.value = False # mesh.attributes.remove(mesh.attributes["sharp_edge"]) if "sharp_face" in mesh.attributes: for sf in mesh.attributes["sharp_face"].data: sf.value = False # mesh.attributes.remove(mesh.attributes["sharp_face"]) # Get loop normals # Since we're calculating them rather than taking them from an imported FBX, # mesh.auto_smooth_angle and mesh.use_auto_smooth affect the calculated split normals. # Issues only appear to occur where the split normals create sharp edges. # auto_smooth_angle of zero will ensure calculated split normals result in sharp edges. mesh.auto_smooth_angle = 0 mesh.use_auto_smooth = True mesh.calc_normals_split() loop_normals = [l.normal for l in mesh.loops] # Set loop normals mesh.normals_split_custom_set(loop_normals) ``` The top meshes are duplicates of the below meshes that have then had the script run on them. ![image](/attachments/22e72c7d-b685-4c9e-987e-beda3731f046)

image.png

501 KiB

We are missing reproducible case here though, please attach the FBX file.

@mont29 I can reproduce in:
Default cube > export fbx > import this fbx > look at this.
So i counted description as enough

Example file is added

> We are missing reproducible case here though, please attach the FBX file. @mont29 I can reproduce in: Default cube > export fbx > import this fbx > look at this. So i counted description as enough _Example file is added_

@Mysteryem thanks, then this is quite obviously an issue with the recent Mesh editing changes.

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Regression: Imported FBX has wrong vertex normals/sharp edges in 3.6 Beta #108170