USD Alab v2 import errors #100452

New Issue

Michael Kowalski · 2022-08-17T03:55:27+02:00

Michael Kowalski commented

2022-08-17 03:55:27 +02:00

When loading the latest version of the Alab scene (v2), materials don't render correctly. I've narrowed the problem down to the following issues:

Some of the UV primvars in the Alab scene are of type Float2Array which is unusual. The Blender USD importer expects UV primvars to be of type TexCoord (e.g., TexCoord2fArray). Hence, some of the Alab UV maps are not getting imported, resulting in the wrong UVs getting applied in the Blender scene. The importer logic should be extended to import Float2Array primvars as texture coordinates as well.
The USD importer is attempting to read the varname input of the UsdPrimvarReader_float2 shader as a TfToken, which conforms to the original UsdPreviewSurface specification. However, in the latest specification, varname is a string. This type mismatch when reading the input can result in an empty map name in the UV Map node in Blender and the wrong texture coordinates getting applies.
For materials that have an authored opacity value, the importer sets the material Blend Mode to Alpha Blend. In the Alab scene this causes artifacts due to object sorting issues. Setting the Blend Mode to Alpha Hashed provides improved results.

To reproduce the issue, the Alab USD can be downloaded here:

https://animallogic.com/alab/

I created branch tmp-usd-alab-v2-#100452 with work in progress on fixes so far.

When loading the latest version of the Alab scene (v2), materials don't render correctly. I've narrowed the problem down to the following issues: - Some of the UV primvars in the Alab scene are of type `Float2Array` which is unusual. The Blender USD importer expects UV primvars to be of type `TexCoord` (e.g., `TexCoord2fArray`). Hence, some of the Alab UV maps are not getting imported, resulting in the wrong UVs getting applied in the Blender scene. The importer logic should be extended to import `Float2Array` primvars as texture coordinates as well. - The USD importer is attempting to read the `varname` input of the `UsdPrimvarReader_float2` shader as a `TfToken`, which conforms to the original `UsdPreviewSurface` specification. However, in the latest specification, `varname` is a string. This type mismatch when reading the input can result in an empty map name in the `UV Map` node in Blender and the wrong texture coordinates getting applies. - For materials that have an authored opacity value, the importer sets the material `Blend Mode` to `Alpha Blend`. In the Alab scene this causes artifacts due to object sorting issues. Setting the `Blend Mode` to `Alpha Hashed` provides improved results. To reproduce the issue, the Alab USD can be downloaded here: https://animallogic.com/alab/ I created branch `tmp-usd-alab-v2-#100452` with work in progress on fixes so far.

Michael Kowalski self-assigned this 2022-08-17 03:55:27 +02:00

Michael Kowalski commented

2022-08-17 03:55:27 +02:00

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

Michael Kowalski commented

2022-08-17 03:55:27 +02:00

Added subscriber: @makowalski

Michael Kowalski commented

2022-08-17 04:49:14 +02:00

Added subscriber: @deadpin

Steffen Dünner commented

2022-08-17 08:10:02 +02:00

Added subscriber: @SteffenD

Jesse Yurkovich commented

2022-08-17 08:52:00 +02:00

The glass beakers are also problematic in Cycles. The material graph is different than what a typical Glass shader would look like.

After import	After manual fixup

Typically the material would modify Transmission for the non-opaque parts (have to invert the Opacity texture) and the Base Color modulates the glass color itself (unsure how the BaseColor texture can be used here at all) -- see screenshots for what both of those textures look like.

The glass beakers are also problematic in Cycles. The material graph is different than what a typical Glass shader would look like. | After import | After manual fixup | | -- | -- | | ![broken-glass.png](https://archive.blender.org/developer/F13396208/broken-glass.png) | ![slightly-better-glass.png](https://archive.blender.org/developer/F13396222/slightly-better-glass.png) | Typically the material would modify Transmission for the non-opaque parts (have to invert the Opacity texture) and the Base Color modulates the glass color itself (unsure how the BaseColor texture can be used here at all) -- see screenshots for what both of those textures look like.

Michael Kowalski commented

2022-08-17 14:42:46 +02:00

Thanks for this insight, @deadpin. This is very helpful. I'll add this to the list of issues.

Hans Goudey commented

2022-08-17 15:11:29 +02:00

Added subscriber: @HooglyBoogly

Hans Goudey commented

2022-08-17 15:11:29 +02:00

For the UV vs. float2 issue, it might be helpful that we'll be moving away from the separation of "UV" and "float2" types, as part of the move to generic attributes.
D14365 implements most of that change, and will most likely be part of 3.4 or 3.5.

For the UV vs. float2 issue, it might be helpful that we'll be moving away from the separation of "UV" and "float2" types, as part of the move to generic attributes. [D14365](https://archive.blender.org/developer/D14365) implements most of that change, and will most likely be part of 3.4 or 3.5.

Michael Kowalski commented

2022-08-17 15:38:58 +02:00

@HooglyBoogly This is very helpful to know, in rethinking how the USD importer handles primvars in general. Thanks!

Thomas Dinges commented

2022-08-17 17:12:20 +02:00

Added subscriber: @ThomasDinges

Ashley commented

2022-09-21 15:05:21 +02:00

Added subscriber: @expenses

Michael Kowalski commented

2022-09-23 22:22:53 +02:00

I've been looking into the UDIM load errors for this scene. Oddly, this might be an issue only when loading EXRs. If I convert the textures to PNG, the UDIMs appear to load correctly in the same scene. I've managed to reproduce the issue on a single mesh in two separate blend files in the attached zip file. The alab_chair_exr_udim.blend file, referencing the EXRs, displays incorrectly in the viewport (first image). The alab_chair_png_udim.blend file, referencing PNGs, displays correctly (second image).

@deadpin By any chance, are you able to reproduce this issue with the attached files?

blender_exr_udim_bug.zip

I've been looking into the UDIM load errors for this scene. Oddly, this might be an issue only when loading EXRs. If I convert the textures to PNG, the UDIMs appear to load correctly in the same scene. I've managed to reproduce the issue on a single mesh in two separate blend files in the attached zip file. The `alab_chair_exr_udim.blend` file, referencing the EXRs, displays incorrectly in the viewport (first image). The `alab_chair_png_udim.blend` file, referencing PNGs, displays correctly (second image). @deadpin By any chance, are you able to reproduce this issue with the attached files? ![image.png](https://archive.blender.org/developer/F13561239/image.png) ![image.png](https://archive.blender.org/developer/F13561235/image.png) [blender_exr_udim_bug.zip](https://archive.blender.org/developer/F13561241/blender_exr_udim_bug.zip)

Jesse Yurkovich commented

2022-09-23 23:04:11 +02:00

Hmm, indeed. It seems to be when the EXRs have a "pass" specified (see below). Some of the EXRs do work, whereas others encounter some confusion. I don't have a good idea of where the problem might be but please file an issue specific to this and I'll try to look this weekend.

ok	not ok - uses a named pass called 'rgb'

Hmm, indeed. It seems to be when the EXRs have a "pass" specified (see below). Some of the EXRs do work, whereas others encounter some confusion. I don't have a good idea of where the problem might be but please file an issue specific to this and I'll try to look this weekend. | ok | not ok - uses a named pass called 'rgb' | | -- | -- | | ![ok.png](https://archive.blender.org/developer/F13561308/ok.png) | ![not-ok.png](https://archive.blender.org/developer/F13561310/not-ok.png) |

Michael Kowalski commented

2022-09-23 23:53:39 +02:00

Thank you so much for looking into this, @deadpin! I created #101320. No rush, this can certainly wait till after the weekend!