Alembic import with animated normals causes incorrect shading #100164

New Issue

Steffen Dünner · 2022-08-03T11:00:52+02:00

Steffen Dünner commented

2022-08-03 11:00:52 +02:00

System Information
Operating system: Linux-5.15.0-43-generic-x86_64-with-glibc2.31 64 Bits
Graphics card: NVIDIA GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 515.65.01

Blender Version
Broken: version: 3.4.0 Alpha, branch: master, commit date: 2022-08-03 07:31, hash: d269fb1d72
Worked: (newest version of Blender that worked as expected)

Short description of error
I noticed that the shading of a simulation imported as an Alembic from Houdini shows incorrect vertex (or face varying) normals:

The same frame of the animation transferred with OBJ looks correct:

I re-imported the Alembic in Houdini and also in Fusion 9 (these were the only two apps with Alembic support I have access to here). Both look and render correct, too:

Houdini

Fusion

The normals themselves aren't even animated but according to abcinfo they are marked as "animated":

/home/steffen/Downloads/explosion_small.abc, version: 10803 (2 timings)
   TimeSample[0]      1 samples:  t0=0 (frame 0.0 @ 24fps)
   TimeSample[1]      2 samples:  t0=1.36 (frame 32.6 @ 24fps)

Objects:
/alembic1 (Xform)
    Constant-Identity
/alembic1/alembic1 (PolyMesh)
  Attribute Animation t0=1.36 (frame 32.6 @ 24fps)
    box fpreal64 .selfBounds[6] (animated[2]) t0=1.36 (frame 32.6 @ 24fps)
    int32 .face-counts
    int32 .face-indices
    point float32 P[3] (animated[2]) t0=1.36 (frame 32.6 @ 24fps)
    FaceVarying float32 N[3] (animated[2]) t0=1.36 (frame 32.6 @ 24fps)
    vector float32 v[3] (animated[2]) t0=1.36 (frame 32.6 @ 24fps)
/alembic1/alembic1/glass_radialinside (FaceSet)
/alembic1/alembic1/glass_concentricoutside (FaceSet)
/alembic1/alembic1/glass_radialoutside (FaceSet)
/alembic1/alembic1/glass_chips (FaceSet)
/alembic1/alembic1/glass_chippinginside (FaceSet)
/alembic1/alembic1/outside (FaceSet)
/alembic1/alembic1/glass_concentricinside (FaceSet)
/alembic1/alembic1/inside (FaceSet)
/alembic1/alembic1/glass_chippingoutside (FaceSet)

11 Objects displayed

Exact steps for others to reproduce the error

Import the attached Alembic (boiled down to only two frames to keep the data size small)
explosion_small.abc
Look at the shading
Now import the OBJ coming from the same simulation
explosion_frame_34.obj

**System Information** Operating system: Linux-5.15.0-43-generic-x86_64-with-glibc2.31 64 Bits Graphics card: NVIDIA GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 515.65.01 **Blender Version** Broken: version: 3.4.0 Alpha, branch: master, commit date: 2022-08-03 07:31, hash: `d269fb1d72` Worked: (newest version of Blender that worked as expected) **Short description of error** I noticed that the shading of a simulation imported as an Alembic from Houdini shows incorrect vertex (or face varying) normals: ![Normals_Blender_Alembic.png](https://archive.blender.org/developer/F13333390/Normals_Blender_Alembic.png) The same frame of the animation transferred with OBJ looks correct: ![Normals_Blender_OBJ.png](https://archive.blender.org/developer/F13333393/Normals_Blender_OBJ.png) I re-imported the Alembic in Houdini and also in Fusion 9 (these were the only two apps with Alembic support I have access to here). Both look and render correct, too: Houdini ![Normals_Houdini.png](https://archive.blender.org/developer/F13333400/Normals_Houdini.png) Fusion ![Normals_Fusion.png](https://archive.blender.org/developer/F13333402/Normals_Fusion.png) The normals themselves aren't even animated but according to abcinfo they are marked as "animated": ``` /home/steffen/Downloads/explosion_small.abc, version: 10803 (2 timings) TimeSample[0] 1 samples: t0=0 (frame 0.0 @ 24fps) TimeSample[1] 2 samples: t0=1.36 (frame 32.6 @ 24fps) Objects: /alembic1 (Xform) Constant-Identity /alembic1/alembic1 (PolyMesh) Attribute Animation t0=1.36 (frame 32.6 @ 24fps) box fpreal64 .selfBounds[6] (animated[2]) t0=1.36 (frame 32.6 @ 24fps) int32 .face-counts int32 .face-indices point float32 P[3] (animated[2]) t0=1.36 (frame 32.6 @ 24fps) FaceVarying float32 N[3] (animated[2]) t0=1.36 (frame 32.6 @ 24fps) vector float32 v[3] (animated[2]) t0=1.36 (frame 32.6 @ 24fps) /alembic1/alembic1/glass_radialinside (FaceSet) /alembic1/alembic1/glass_concentricoutside (FaceSet) /alembic1/alembic1/glass_radialoutside (FaceSet) /alembic1/alembic1/glass_chips (FaceSet) /alembic1/alembic1/glass_chippinginside (FaceSet) /alembic1/alembic1/outside (FaceSet) /alembic1/alembic1/glass_concentricinside (FaceSet) /alembic1/alembic1/inside (FaceSet) /alembic1/alembic1/glass_chippingoutside (FaceSet) 11 Objects displayed ``` **Exact steps for others to reproduce the error** - Import the attached Alembic (boiled down to only two frames to keep the data size small) [explosion_small.abc](https://archive.blender.org/developer/F13333404/explosion_small.abc) - Look at the shading - Now import the OBJ coming from the same simulation [explosion_frame_34.obj](https://archive.blender.org/developer/F13333408/explosion_frame_34.obj)

Steffen Dünner commented

2022-08-03 11:00:52 +02:00

Added subscriber: @SteffenD

Steffen Dünner changed title from ~~Alembic Import with Animated Normals fails~~ to Alembic import with animated normals causes incorrect shading

2022-08-03 11:01:36 +02:00

Steffen Dünner commented

2022-08-03 11:31:03 +02:00

Just gave animated UVs and normals a try by animating the UVs and normals of a simple grid in Blender, exporting it to Alembic and re-importing it. They both work.
Abcinfo for the animated normals looks very similar to the one coming from Houdini. I wonder why only the one coming from Blender has proper animated normals:

/home/steffen/Downloads/Animated_Normals_v01.abc, version: 10803 (2 timings)
   TimeSample[0]      1 samples:  t0=0 (frame 0.0 @ 24fps)
   TimeSample[1]    250 samples:  t0=0.04 (frame 1.0 @ 24fps)

Objects:
/Grid (Xform)
    Constant-Identity
/Grid/Grid (PolyMesh)
    box fpreal64 .selfBounds[6]
    int32 .face-counts
    int32 .face-indices
    point float32 P[3]
    FaceVarying float32 N[3] (animated[250]) t0=0.04 (frame 1.0 @ 24fps)
    FaceVarying float32 uv[2]
     uint8 meshtype

2 Objects displayed

Or am I barking up the wrong tree?
Animated_Normals_v01.abc

Just gave animated UVs and normals a try by animating the UVs and normals of a simple grid in Blender, exporting it to Alembic and re-importing it. They both work. Abcinfo for the animated normals looks very similar to the one coming from Houdini. I wonder why only the one coming from Blender has proper animated normals: ``` /home/steffen/Downloads/Animated_Normals_v01.abc, version: 10803 (2 timings) TimeSample[0] 1 samples: t0=0 (frame 0.0 @ 24fps) TimeSample[1] 250 samples: t0=0.04 (frame 1.0 @ 24fps) Objects: /Grid (Xform) Constant-Identity /Grid/Grid (PolyMesh) box fpreal64 .selfBounds[6] int32 .face-counts int32 .face-indices point float32 P[3] FaceVarying float32 N[3] (animated[250]) t0=0.04 (frame 1.0 @ 24fps) FaceVarying float32 uv[2] uint8 meshtype 2 Objects displayed ``` Or am I barking up the wrong tree? [Animated_Normals_v01.abc](https://archive.blender.org/developer/F13333450/Animated_Normals_v01.abc)

Omar Emara commented

2022-08-03 14:04:46 +02:00

Added subscriber: @OmarEmaraDev

Omar Emara commented

2022-08-03 14:04:46 +02:00

I hit an asset when going to edit mode in a debug build, maybe that is related, investigating the normals issue.

* thread #1, name = 'blender', stop reason = signal SIGABRT
  * frame #0: 0x00007ffff7c8e36c libc.so.6`___lldb_unnamed_symbol3484 + 284
    frame #1: 0x00007ffff7c3e838 libc.so.6`raise + 24
    frame #2: 0x00007ffff7c28535 libc.so.6`abort + 207
    frame #3: 0x0000000000c3b8d0 blender`bmesh_elem_check(element=0x00007fffc4d93488, htype='\b') at bmesh_core.c:697:3
    frame #4: 0x0000000000c3c319 blender`BM_face_create(bm=0x00007fffd2f2f108, verts=0x00007fffffffd148, edges=0x00007fffffffd038, len=13, f_example=0x0000000000000000, create_flag=BM_CREATE_SKIP_CD) at bmesh_core.c:459:3
    frame #5: 0x0000000000ca1d55 blender`bm_face_create_from_mpoly(bm=0x00007fffd2f2f108, loops=Span<MLoop> @ 0x00007fffffffd018, vtable=Span<BMVert *> @ 0x00007fffffffd008, etable=Span<BMEdge *> @ 0x00007fffffffd260) at bmesh_mesh_convert.cc:201:10
    frame #6: 0x0000000000ca1345 blender`::BM_mesh_bm_from_me(bm=0x00007fffd2f2f108, me=0x00007fffc5225008, params=0x00007fffffffd8a0) at bmesh_mesh_convert.cc:439:17
    frame #7: 0x000000000070f7d7 blender`::BKE_mesh_to_bmesh_ex(me=0x00007fffc5225008, create_params=0x00007fffffffd920, convert_params=0x00007fffffffd8a0) at mesh.cc:1141:3
    frame #8: 0x000000000070f87a blender`::BKE_mesh_to_bmesh(me=0x00007fffc5225008, ob=0x00007fffc523a008, add_key_index=false, params=0x00007fffffffd920) at mesh.cc:1157:10
    frame #9: 0x0000000001dab307 blender`EDBM_mesh_make(ob=0x00007fffc523a008, select_mode=1, add_key_index=false) at editmesh_utils.c:274:8
    frame #10: 0x0000000001ded540 blender`ED_object_editmode_enter_ex(bmain=0x00007fffeb74b108, scene=0x00007fffeb87a008, ob=0x00007fffc523a008, flag=0) at object_edit.c:759:5
    frame #11: 0x0000000001dedae1 blender`editmode_toggle_exec(C=0x00007ffff3f81388, op=0x00007fffc6ee5dc8) at object_edit.c:856:5
    frame #12: 0x0000000000a37fe9 blender`wm_operator_invoke(C=0x00007ffff3f81388, ot=0x00007ffff4454f28, event=0x0000000000000000, properties=0x0000000000000000, reports=0x0000000000000000, poll_only=false, use_last_properties=true) at wm_event_system.cc:1401:16
    frame #13: 0x0000000000a2dc12 blender`wm_operator_call_internal(C=0x00007ffff3f81388, ot=0x00007ffff4454f28, properties=0x0000000000000000, reports=0x0000000000000000, context=WM_OP_EXEC_REGION_WIN, poll_only=false, event=0x0000000000000000) at wm_event_system.cc:1594:18
    frame #14: 0x0000000000a2e63a blender`::WM_operator_name_call_ptr(C=0x00007ffff3f81388, ot=0x00007ffff4454f28, context=WM_OP_EXEC_REGION_WIN, properties=0x0000000000000000, event=0x0000000000000000) at wm_event_system.cc:1642:10
    frame #15: 0x0000000001dfd6ac blender`ED_object_mode_set_ex(C=0x00007ffff3f81388, mode=OB_MODE_EDIT, use_undo=true, reports=0x00007fffca572318) at object_modes.c:217:3
    frame #16: 0x0000000001defee9 blender`object_mode_set_exec(C=0x00007ffff3f81388, op=0x00007fffcb6b4e48) at object_edit.c:1721:13
    frame #17: 0x0000000000a37fe9 blender`wm_operator_invoke(C=0x00007ffff3f81388, ot=0x00007ffff4454ba8, event=0x00007fffd2daf308, properties=0x00007fffd2cec468, reports=0x0000000000000000, poll_only=false, use_last_properties=true) at wm_event_system.cc:1401:16
    frame #18: 0x0000000000a3ad96 blender`wm_handler_operator_call(C=0x00007ffff3f81388, handlers=0x00007fffeb820900, handler_base=0x00007fffeae572a8, event=0x00007fffd2daf308, properties=0x00007fffd2cec468, kmi_idname="OBJECT_OT_mode_set") at wm_event_system.cc:2423:16
    frame #19: 0x0000000000a397b7 blender`wm_handlers_do_keymap_with_keymap_handler(C=0x00007ffff3f81388, event=0x00007fffd2daf308, handlers=0x00007fffeb820900, handler=0x00007fffeae572a8, keymap=0x00007fffd2c19288, do_debug_handler=false) at wm_event_system.cc:2815:21
    frame #20: 0x0000000000a38e4c blender`wm_handlers_do_intern(C=0x00007ffff3f81388, win=0x00007fffeb819b88, event=0x00007fffd2daf308, handlers=0x00007fffeb820900) at wm_event_system.cc:3141:26
    frame #21: 0x0000000000a30f0f blender`wm_handlers_do(C=0x00007ffff3f81388, event=0x00007fffd2daf308, handlers=0x00007fffeb820900) at wm_event_system.cc:3281:16
    frame #22: 0x0000000000a3b9de blender`wm_event_do_region_handlers(C=0x00007ffff3f81388, event=0x00007fffd2daf308, region=0x00007fffeb8207c8) at wm_event_system.cc:3700:10
    frame #23: 0x0000000000a32011 blender`wm_event_do_handlers_area_regions(C=0x00007ffff3f81388, event=0x00007fffd2daf308, area=0x00007fffeb811288) at wm_event_system.cc:3730:10
    frame #24: 0x0000000000a302b1 blender`::wm_event_do_handlers(C=0x00007ffff3f81388) at wm_event_system.cc:3926:23
    frame #25: 0x0000000000a22477 blender`WM_main(C=0x00007ffff3f81388) at wm.c:631:5
    frame #26: 0x0000000000230fe9 blender`main(argc=1, argv=0x00007fffffffe9e8) at creator.c:546:5
    frame #27: 0x00007ffff7c29290 libc.so.6`___lldb_unnamed_symbol3123 + 128
    frame #28: 0x00007ffff7c2934a libc.so.6`__libc_start_main + 138
    frame #29: 0x0000000000230ba5 blender`_start at start.S:115

I hit an asset when going to edit mode in a debug build, maybe that is related, investigating the normals issue. ``` * thread #1, name = 'blender', stop reason = signal SIGABRT * frame #0: 0x00007ffff7c8e36c libc.so.6`___lldb_unnamed_symbol3484 + 284 frame #1: 0x00007ffff7c3e838 libc.so.6`raise + 24 frame #2: 0x00007ffff7c28535 libc.so.6`abort + 207 frame #3: 0x0000000000c3b8d0 blender`bmesh_elem_check(element=0x00007fffc4d93488, htype='\b') at bmesh_core.c:697:3 frame #4: 0x0000000000c3c319 blender`BM_face_create(bm=0x00007fffd2f2f108, verts=0x00007fffffffd148, edges=0x00007fffffffd038, len=13, f_example=0x0000000000000000, create_flag=BM_CREATE_SKIP_CD) at bmesh_core.c:459:3 frame #5: 0x0000000000ca1d55 blender`bm_face_create_from_mpoly(bm=0x00007fffd2f2f108, loops=Span<MLoop> @ 0x00007fffffffd018, vtable=Span<BMVert *> @ 0x00007fffffffd008, etable=Span<BMEdge *> @ 0x00007fffffffd260) at bmesh_mesh_convert.cc:201:10 frame #6: 0x0000000000ca1345 blender`::BM_mesh_bm_from_me(bm=0x00007fffd2f2f108, me=0x00007fffc5225008, params=0x00007fffffffd8a0) at bmesh_mesh_convert.cc:439:17 frame #7: 0x000000000070f7d7 blender`::BKE_mesh_to_bmesh_ex(me=0x00007fffc5225008, create_params=0x00007fffffffd920, convert_params=0x00007fffffffd8a0) at mesh.cc:1141:3 frame #8: 0x000000000070f87a blender`::BKE_mesh_to_bmesh(me=0x00007fffc5225008, ob=0x00007fffc523a008, add_key_index=false, params=0x00007fffffffd920) at mesh.cc:1157:10 frame #9: 0x0000000001dab307 blender`EDBM_mesh_make(ob=0x00007fffc523a008, select_mode=1, add_key_index=false) at editmesh_utils.c:274:8 frame #10: 0x0000000001ded540 blender`ED_object_editmode_enter_ex(bmain=0x00007fffeb74b108, scene=0x00007fffeb87a008, ob=0x00007fffc523a008, flag=0) at object_edit.c:759:5 frame #11: 0x0000000001dedae1 blender`editmode_toggle_exec(C=0x00007ffff3f81388, op=0x00007fffc6ee5dc8) at object_edit.c:856:5 frame #12: 0x0000000000a37fe9 blender`wm_operator_invoke(C=0x00007ffff3f81388, ot=0x00007ffff4454f28, event=0x0000000000000000, properties=0x0000000000000000, reports=0x0000000000000000, poll_only=false, use_last_properties=true) at wm_event_system.cc:1401:16 frame #13: 0x0000000000a2dc12 blender`wm_operator_call_internal(C=0x00007ffff3f81388, ot=0x00007ffff4454f28, properties=0x0000000000000000, reports=0x0000000000000000, context=WM_OP_EXEC_REGION_WIN, poll_only=false, event=0x0000000000000000) at wm_event_system.cc:1594:18 frame #14: 0x0000000000a2e63a blender`::WM_operator_name_call_ptr(C=0x00007ffff3f81388, ot=0x00007ffff4454f28, context=WM_OP_EXEC_REGION_WIN, properties=0x0000000000000000, event=0x0000000000000000) at wm_event_system.cc:1642:10 frame #15: 0x0000000001dfd6ac blender`ED_object_mode_set_ex(C=0x00007ffff3f81388, mode=OB_MODE_EDIT, use_undo=true, reports=0x00007fffca572318) at object_modes.c:217:3 frame #16: 0x0000000001defee9 blender`object_mode_set_exec(C=0x00007ffff3f81388, op=0x00007fffcb6b4e48) at object_edit.c:1721:13 frame #17: 0x0000000000a37fe9 blender`wm_operator_invoke(C=0x00007ffff3f81388, ot=0x00007ffff4454ba8, event=0x00007fffd2daf308, properties=0x00007fffd2cec468, reports=0x0000000000000000, poll_only=false, use_last_properties=true) at wm_event_system.cc:1401:16 frame #18: 0x0000000000a3ad96 blender`wm_handler_operator_call(C=0x00007ffff3f81388, handlers=0x00007fffeb820900, handler_base=0x00007fffeae572a8, event=0x00007fffd2daf308, properties=0x00007fffd2cec468, kmi_idname="OBJECT_OT_mode_set") at wm_event_system.cc:2423:16 frame #19: 0x0000000000a397b7 blender`wm_handlers_do_keymap_with_keymap_handler(C=0x00007ffff3f81388, event=0x00007fffd2daf308, handlers=0x00007fffeb820900, handler=0x00007fffeae572a8, keymap=0x00007fffd2c19288, do_debug_handler=false) at wm_event_system.cc:2815:21 frame #20: 0x0000000000a38e4c blender`wm_handlers_do_intern(C=0x00007ffff3f81388, win=0x00007fffeb819b88, event=0x00007fffd2daf308, handlers=0x00007fffeb820900) at wm_event_system.cc:3141:26 frame #21: 0x0000000000a30f0f blender`wm_handlers_do(C=0x00007ffff3f81388, event=0x00007fffd2daf308, handlers=0x00007fffeb820900) at wm_event_system.cc:3281:16 frame #22: 0x0000000000a3b9de blender`wm_event_do_region_handlers(C=0x00007ffff3f81388, event=0x00007fffd2daf308, region=0x00007fffeb8207c8) at wm_event_system.cc:3700:10 frame #23: 0x0000000000a32011 blender`wm_event_do_handlers_area_regions(C=0x00007ffff3f81388, event=0x00007fffd2daf308, area=0x00007fffeb811288) at wm_event_system.cc:3730:10 frame #24: 0x0000000000a302b1 blender`::wm_event_do_handlers(C=0x00007ffff3f81388) at wm_event_system.cc:3926:23 frame #25: 0x0000000000a22477 blender`WM_main(C=0x00007ffff3f81388) at wm.c:631:5 frame #26: 0x0000000000230fe9 blender`main(argc=1, argv=0x00007fffffffe9e8) at creator.c:546:5 frame #27: 0x00007ffff7c29290 libc.so.6`___lldb_unnamed_symbol3123 + 128 frame #28: 0x00007ffff7c2934a libc.so.6`__libc_start_main + 138 frame #29: 0x0000000000230ba5 blender`_start at start.S:115 ```

Omar Emara commented

2022-08-03 14:54:08 +02:00

It is interesting to note that the new OBJ importer suffered from the same issue in 3.2, but it works correctly in 3.4, so it must have fixed something.

Attached is a dump of the normals from the alembic and obj files attached above. There are differences between both.

obj_normals.txt

alembic_normals.txt

The following returns an array with 9776 elements.

numpy.argwhere(numpy.max(numpy.abs(numpy.loadtxt("alembic_normals.txt") - numpy.loadtxt("obj_normals.txt")), axis = 1) > 0.1)

It is interesting to note that the new OBJ importer suffered from the same issue in 3.2, but it works correctly in 3.4, so it must have fixed something. Attached is a dump of the normals from the alembic and obj files attached above. There are differences between both. [obj_normals.txt](https://archive.blender.org/developer/F13333750/obj_normals.txt) [alembic_normals.txt](https://archive.blender.org/developer/F13333749/alembic_normals.txt) The following returns an array with 9776 elements. ``` numpy.argwhere(numpy.max(numpy.abs(numpy.loadtxt("alembic_normals.txt") - numpy.loadtxt("obj_normals.txt")), axis = 1) > 0.1) ```

Omar Emara commented

2022-08-03 15:21:51 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Omar Emara commented

2022-08-03 15:21:51 +02:00

Looks like normals just need to be normalized.

diff --git a/source/blender/io/alembic/intern/abc_reader_mesh.cc b/source/blender/io/alembic/intern/abc_reader_mesh.cc
index bacc1f06599..74e0b0dd1ae 100644
--- a/source/blender/io/alembic/intern/abc_reader_mesh.cc
+++ b/source/blender/io/alembic/intern/abc_reader_mesh.cc
@@ -277,6 +277,7 @@ static void process_loop_normals(CDStreamConfig &config, const N3fArraySamplePtr
     for (int j = mpoly->totloop - 1; j >= 0; j--, abc_index++) {
       int blender_index = mpoly->loopstart + j;
       copy_zup_from_yup(lnors[blender_index], loop_normals[abc_index].getValue());
+      normalize_v3(lnors[blender_index]);
     }
   }

Above patch is just for testing, probably need to normalize other normal processors as well.

Looks like normals just need to be normalized. ``` diff --git a/source/blender/io/alembic/intern/abc_reader_mesh.cc b/source/blender/io/alembic/intern/abc_reader_mesh.cc index bacc1f06599..74e0b0dd1ae 100644 --- a/source/blender/io/alembic/intern/abc_reader_mesh.cc +++ b/source/blender/io/alembic/intern/abc_reader_mesh.cc @@ -277,6 +277,7 @@ static void process_loop_normals(CDStreamConfig &config, const N3fArraySamplePtr for (int j = mpoly->totloop - 1; j >= 0; j--, abc_index++) { int blender_index = mpoly->loopstart + j; copy_zup_from_yup(lnors[blender_index], loop_normals[abc_index].getValue()); + normalize_v3(lnors[blender_index]); } } ``` Above patch is just for testing, probably need to normalize other normal processors as well.

Steffen Dünner commented

2022-08-04 09:13:02 +02:00

In #100164#1399261, @OmarEmaraDev wrote:
Looks like normals just need to be normalized.

Wow! Thanks for investigating the issue and finding the problem.
Because we don't have access to setting normals in Geometry Nodes yet, I went back to Houdini, imported the "explosion_small.abc", normalized the normals (pun intended ;) ) and re-exported an Alembic.
It displays and renders perfectly in Blender. I hope your fix finds a way into master soon.
Here's the normalized version of the Alembic:
explosion_small_normalized.abc

BTW the very same goes for USD import: The normals need to be normalized there as well. Here's the "explosion_small.abc" converted to USD which also shows the problem when imported in Blender:
explosion_small.usd

> In #100164#1399261, @OmarEmaraDev wrote: > Looks like normals just need to be normalized. Wow! Thanks for investigating the issue and finding the problem. Because we don't have access to setting normals in Geometry Nodes yet, I went back to Houdini, imported the "explosion_small.abc", normalized the normals (pun intended ;) ) and re-exported an Alembic. It displays and renders perfectly in Blender. I hope your fix finds a way into master soon. Here's the normalized version of the Alembic: [explosion_small_normalized.abc](https://archive.blender.org/developer/F13335764/explosion_small_normalized.abc) BTW the very same goes for USD import: The normals need to be normalized there as well. Here's the "explosion_small.abc" converted to USD which also shows the problem when imported in Blender: [explosion_small.usd](https://archive.blender.org/developer/F13335761/explosion_small.usd)

Steffen Dünner commented

2022-08-04 09:43:30 +02:00

And another quick addition:
The Alembics and USDs with normalized normals render fine BUT as soon as I switch on motion blur another problem occurs which I reported a few days ago: https://developer.blender.org/T100134

Here's a rendering without MB:

and MB on:

EDIT: Eevee renders motion blur and shading fine

And another quick addition: The Alembics and USDs with normalized normals render fine BUT as soon as I switch on motion blur another problem occurs which I reported a few days ago: https://developer.blender.org/T100134 Here's a rendering without MB: ![MB_Off.png](https://archive.blender.org/developer/F13335799/MB_Off.png) and MB on: ![MB_On.png](https://archive.blender.org/developer/F13335801/MB_On.png) EDIT: Eevee renders motion blur and shading fine

Bastien Montagne added this to the Pipeline, Assets & IO project 2023-02-09 15:39:30 +01:00

Philipp Oeser removed the

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Alembic import with animated normals causes incorrect shading #100164