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USD export: Fix incorrect texture alpha mapping. #107022

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Michael Kowalski merged 8 commits from makowalski/blender:usd_preview_surface_alpha_bug into main 2023-05-03 16:13:00 +02:00
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Michael Kowalski commented 2023-04-17 03:31:07 +02:00
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This addresses bug #105621.

Fixed bug where texture alpha was incorrectly remapped to red when exporting material shaders.

Now connecting the UsdPreviewSurface opacity input to the UsdUVTexture a output if the Blender texture image node source socket identifier is Alpha.

Specific changes include the following:

  • The InputSpec::source_name struct member was removed, as the connection source name is now determined at runtime based on the Blender node input socket identifier.
  • The traverse_channel() utility function now returns a bNodeLink*, so that the source socket identifier can be queried from the link.
  • In create_usd_preview_surface_materia(), the code for creating and connecting a UsdUVTexture shader was reorganized to group it within one conditional block, to make it easier to follow. Also replaced a call to a deprecated version of UsdShadeInput::ConnectToSource().

To test, open the attached test_usd_preview_surface_alpha.blend file, export to USD and open the exported file in the usdview application. The attached two images show the displayed texture before and after the fix, respectively. Note the incorrect opacities in the first image demonstrating the bug, where regions that should be blue are transparent.

This addresses bug #105621. Fixed bug where texture alpha was incorrectly remapped to red when exporting material shaders. Now connecting the `UsdPreviewSurface` `opacity` input to the `UsdUVTexture` `a` output if the Blender texture image node source socket identifier is Alpha. Specific changes include the following: - The `InputSpec::source_name` struct member was removed, as the connection source name is now determined at runtime based on the Blender node input socket identifier. - The `traverse_channel()` utility function now returns a `bNodeLink*`, so that the source socket identifier can be queried from the link. - In `create_usd_preview_surface_materia()`, the code for creating and connecting a `UsdUVTexture` shader was reorganized to group it within one conditional block, to make it easier to follow. Also replaced a call to a deprecated version of `UsdShadeInput::ConnectToSource()`. To test, open the attached `test_usd_preview_surface_alpha.blend` file, export to USD and open the exported file in the `usdview` application. The attached two images show the displayed texture before and after the fix, respectively. Note the incorrect opacities in the first image demonstrating the bug, where regions that should be blue are transparent.
usd_preview_surface_alpha_bug.PNG
390 KiB
test_usd_preview_surface_alpha.blend
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usd_preview_surface_alpha_fixed.PNG
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usd_preview_surface_alpha_bug.PNG usd_preview_surface_alpha_fixed.PNG
Michael Kowalski added 1 commit 2023-04-17 03:31:24 +02:00
0c2b8df986 USD export: Fix incorrect texture alpha mapping. 
This addresses bug #105621.

Fixed bug where texture alpha was incorrectly remapped to red.
Now connecting the UsdPreviewSurface "opacity" input to the
UsdUVTexture "a" output.
Michael Kowalski added the
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Michael Kowalski requested review from Jesse Yurkovich 2023-04-17 16:08:31 +02:00
Michael Kowalski added this to the USD project 2023-04-17 18:20:52 +02:00
Matt McLin commented 2023-04-17 19:26:50 +02:00
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I wonder if something more nuanced is needed here. Using the alpha channel for opacity generally makes sense, but I have also encountered materials that use a single-channel texture for opacity, in which case I see the red channel is used. Perhaps the important thing here is to preserve however the material/shader was authored instead of making an assumption about the correct channel?

I wonder if something more nuanced is needed here. Using the alpha channel for opacity generally makes sense, but I have also encountered materials that use a single-channel texture for opacity, in which case I see the red channel is used. Perhaps the important thing here is to preserve however the material/shader was authored instead of making an assumption about the correct channel?
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Jesse Yurkovich commented 2023-04-18 08:18:42 +02:00
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Hmm, without full material graph translation between USD <--> Blender, it will not be possible to be correct in all situations here. Only the following nodes are supported, which isn't enough to accurately describe most general graphs: https://docs.blender.org/manual/en/3.6/files/import_export/usd.html#materials

This patch here is probably ok as a small step forward. But, outside of the exact scenario listed in the bug, things will still be problematic until we can land a design/implementation for things like MaterialX and make decisions on what to do about Blender nodes that aren't compatible with that ecosystem and vice versa.

E.g. Similar to the scenario that Matt describes above:

Original (native scene) After USD Export and Import (this patch)
usd-setup.png usd-result.png
Hmm, without full material graph translation between USD <--> Blender, it will not be possible to be correct in all situations here. Only the following nodes are supported, which isn't enough to accurately describe most general graphs: https://docs.blender.org/manual/en/3.6/files/import_export/usd.html#materials This patch here is probably ok as a small step forward. But, outside of the exact scenario listed in the bug, things will still be problematic until we can land a design/implementation for things like MaterialX and make decisions on what to do about Blender nodes that aren't compatible with that ecosystem and vice versa. E.g. Similar to the scenario that Matt describes above: | Original (native scene) | After USD Export and Import (this patch) | | -- | -- | | ![usd-setup.png](/attachments/71220514-b2ce-4606-818b-48302b9ff92d) | ![usd-result.png](/attachments/fe7ad542-b77d-4872-aa38-9e691ba79c9e) |
usd-setup.png
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usd-result.png
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Michael Kowalski commented 2023-04-18 21:42:52 +02:00
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I wonder if something more nuanced is needed here. Using the alpha channel for opacity generally makes sense, but I have also encountered materials that use a single-channel texture for opacity, in which case I see the red channel is used. Perhaps the important thing here is to preserve however the material/shader was authored instead of making an assumption about the correct channel?

That's a good point. I am reworking the logic to take the source connection into account.

> I wonder if something more nuanced is needed here. Using the alpha channel for opacity generally makes sense, but I have also encountered materials that use a single-channel texture for opacity, in which case I see the red channel is used. Perhaps the important thing here is to preserve however the material/shader was authored instead of making an assumption about the correct channel? That's a good point. I am reworking the logic to take the source connection into account.
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Michael Kowalski commented 2023-04-18 21:58:30 +02:00
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Hmm, without full material graph translation between USD <--> Blender, it will not be possible to be correct in all situations here. Only the following nodes are supported, which isn't enough to accurately describe most general graphs: https://docs.blender.org/manual/en/3.6/files/import_export/usd.html#materials

This is very true, @deadpin. I appreciate that observation. The current material conversion code doesn't aim to cover all possible graphs, obviously. The intent was to try to handle the case where complex shaders have been baked to textures. Adding logic to handle the Separate XYZ node could help in this case, and I'm looking into implementing this as well.

> Hmm, without full material graph translation between USD <--> Blender, it will not be possible to be correct in all situations here. Only the following nodes are supported, which isn't enough to accurately describe most general graphs: https://docs.blender.org/manual/en/3.6/files/import_export/usd.html#materials This is very true, @deadpin. I appreciate that observation. The current material conversion code doesn't aim to cover all possible graphs, obviously. The intent was to try to handle the case where complex shaders have been baked to textures. Adding logic to handle the `Separate XYZ` node could help in this case, and I'm looking into implementing this as well.
Michael Kowalski commented 2023-04-18 22:19:49 +02:00
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@deadpin I will also be addressing the issue of the duplicated nodes on re-import in a separate patch.

@deadpin I will also be addressing the issue of the duplicated nodes on re-import in a separate patch.
Michael Kowalski added 4 commits 2023-04-25 21:35:56 +02:00
530a728307 USD Preview Texture import: handle alpha source name. 
Updated logic for connecting texture inputs to set the
UsdUVTexture source name to "a" if the Blender node
source socket identifier is Alpha.
Michael Kowalski added 1 commit 2023-04-25 22:18:43 +02:00
Michael Kowalski commented 2023-04-25 22:34:17 +02:00
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@Matt-McLin I updated the logic for connecting texture inputs to take the Blender node source socket identifier into account when determining the UsdUVTexture source name.

@deadpin With the latest changes, the code no longer uses hard coded UsdUVTexture source names. This logic can be extended in the future to set the appropriate source names when converting Blender Separate XYZ shaders. However, I believe handling Separate XYZ shaders should be implemented in a separate pull request.

@Matt-McLin I updated the logic for connecting texture inputs to take the Blender node source socket identifier into account when determining the `UsdUVTexture` source name. @deadpin With the latest changes, the code no longer uses hard coded `UsdUVTexture` source names. This logic can be extended in the future to set the appropriate source names when converting Blender `Separate XYZ` shaders. However, I believe handling `Separate XYZ` shaders should be implemented in a separate pull request.
Jesse Yurkovich approved these changes 2023-04-26 07:10:04 +02:00
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Seems ok to me. I was only able to validate that round-tripping the provided .blend file works. usdview is still giving me grief on my machine so I can't validate there, but the exported .usda file seems correct.

Seems ok to me. I was only able to validate that round-tripping the provided .blend file works. usdview is still giving me grief on my machine so I can't validate there, but the exported .usda file seems correct.
Michael Kowalski commented 2023-04-27 00:41:28 +02:00
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Thanks for the reviews, @deadpin and @Matt-McLin!

@Matt-McLin Just FYI, I'll hold off on committing this pull request until after pull

#107149

is finished and committed, since that pull touches the same code.

Thanks for the reviews, @deadpin and @Matt-McLin! @Matt-McLin Just FYI, I'll hold off on committing this pull request until after pull https://projects.blender.org/blender/blender/pulls/107149 is finished and committed, since that pull touches the same code.
Matt McLin commented 2023-04-27 19:05:28 +02:00
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Thanks, Michael, this looks good to me. Sorry about wait on #107149, have been traveling all week, planning to get the change up tomorrow.

Thanks, Michael, this looks good to me. Sorry about wait on #107149, have been traveling all week, planning to get the change up tomorrow.
Michael Kowalski commented 2023-04-27 20:16:14 +02:00
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Thanks, Michael, this looks good to me. Sorry about wait on #107149, have been traveling all week, planning to get the change up tomorrow.

Thanks for the update, Matt. No worries about any delays.

> Thanks, Michael, this looks good to me. Sorry about wait on #107149, have been traveling all week, planning to get the change up tomorrow. Thanks for the update, Matt. No worries about any delays.
Michael Kowalski added 2 commits 2023-05-02 18:49:36 +02:00
buildbot/vexp-code-patch-coordinator Build done. Details
e5d609e45f Format fix.
Michael Kowalski commented 2023-05-02 18:56:54 +02:00
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@Matt-McLin I merged in the recently committed logic to set opacityThreshold from

#107149

Note that I refactored that logic somewhat to consolidate the code in one conditional block, since this is the approach I'm taking in the current patch. I verified that the opacityThreshold test still passes, but please let me know if this change is okay.

@Matt-McLin I merged in the recently committed logic to set `opacityThreshold` from https://projects.blender.org/blender/blender/pulls/107149 Note that I refactored that logic somewhat to consolidate the code in one conditional block, since this is the approach I'm taking in the current patch. I verified that the `opacityThreshold` test still passes, but please let me know if this change is okay.
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Matt McLin commented 2023-05-03 01:26:11 +02:00
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Thanks, Michael, yes, the refactor for opacityThreshold looks good to me.

Thanks, Michael, yes, the refactor for `opacityThreshold` looks good to me.
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Michael Kowalski commented 2023-05-03 15:43:25 +02:00
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@blender-bot build

@blender-bot build
Michael Kowalski merged commit 109c1b92cd into main 2023-05-03 16:13:00 +02:00
Michael Kowalski deleted branch usd_preview_surface_alpha_bug 2023-05-03 16:13:01 +02:00
Howard Trickey referenced this issue from a commit 2023-05-29 02:51:42 +02:00
Merge in orign/main:
Bastien Montagne removed this from the USD project 2023-08-25 23:52:28 +02:00
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