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USD Importer - not respecting output channels #96458

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opened 2022-03-14 17:44:28 +01:00 by Steven Craft · 21 comments
Steven Craft commented 2022-03-14 17:44:28 +01:00
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System Information
Operating system: Windows
Graphics card: NVIDIA GeForce GTX 1060 6GB

Blender Version
Broken: 3.01, dc2d180181, master, 2022-01-25
Worked: N/A

Short description of error

Importing USD files that have specific channels of a texture connected to material properties does not work (the channels aren't separated before being connected to the material properties).

Exact steps for others to reproduce the error

  • Author a USD file that has a texture channel that has metallic in the blue channel and roughness in the green channel
  • Note inside the USD file it specifies that float inputs:metallic.connect = texture:b and float inputs:roughness.connect = texture:g this is correct
  • Import into Blender
  • View the Shading tab and note the full-colour output of the texture is connected to both 'Metallic' and 'Roughness'

Note if you author the same file as GLTF and import that into Blender, it will correctly add a 'Separate RGB' node after the texture, then connect the B output to a 'Metallic Factor' node and then onto the 'Metallic' property, and to the 'Separate RGB' also connect the B output directly to Roughness.

This is how the GLTF shader nodes look:

Blender_GLTF.png

This is how the USD shader nodes look:

Blender_USD.png

**System Information** Operating system: Windows Graphics card: NVIDIA GeForce GTX 1060 6GB **Blender Version** Broken: 3.01, dc2d18018171, master, 2022-01-25 Worked: N/A **Short description of error** Importing USD files that have specific channels of a texture connected to material properties does not work (the channels aren't separated before being connected to the material properties). **Exact steps for others to reproduce the error** - Author a USD file that has a texture channel that has metallic in the blue channel and roughness in the green channel - Note inside the USD file it specifies that float inputs:metallic.connect = <texture:b> and float inputs:roughness.connect = <texture:g> this is correct - Import into Blender - View the Shading tab and note the full-colour output of the texture is connected to both 'Metallic' and 'Roughness' # Note if you author the same file as GLTF and import that into Blender, it will correctly add a 'Separate RGB' node after the texture, then connect the B output to a 'Metallic Factor' node and then onto the 'Metallic' property, and to the 'Separate RGB' also connect the B output directly to Roughness. This is how the GLTF shader nodes look: ![Blender_GLTF.png](https://archive.blender.org/developer/F12927467/Blender_GLTF.png) This is how the USD shader nodes look: ![Blender_USD.png](https://archive.blender.org/developer/F12927466/Blender_USD.png)
Steven Craft commented 2022-03-14 17:44:28 +01:00
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Added subscriber: @scraft

Added subscriber: @scraft
Omar Emara commented 2022-03-21 10:50:55 +01:00
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Added subscriber: @OmarEmaraDev

Added subscriber: @OmarEmaraDev
Omar Emara commented 2022-03-21 10:50:55 +01:00
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Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'
Omar Emara commented 2022-03-21 10:50:55 +01:00
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Can you attach one such file to make testing easier?
But it does seem like the importer ignores all USD tokens except for the alpha one. So this seems like a limitation than a bug. Tagging the appropriate module for more information.

Can you attach one such file to make testing easier? But it does seem like the importer ignores all USD tokens except for the alpha one. So this seems like a limitation than a bug. Tagging the appropriate module for more information.
Steven Craft commented 2022-03-21 11:17:45 +01:00
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As a side note, the GLTF specification is a little more rigid for shininess/roughness and metalicity: https:*www.khronos.org/blog/art-pipeline-for-gltf

The Ambient Occlusion, Roughness, and Metallic textures are saved in a single channel-packed texture to reduce the number of texture loads. The textures need to be packed into the channels of your texture as follows:
Red: Ambient Occlusion
Green: Roughness
Blue: Metallic

I appreciate this is GLTF and therefore doesn't apply directly to USD, but at the same time, the formats do sort of go hand-in-hand, ie if you want to author out assets that will be natively consumed on all devices then you have to export to both GLTF and USD. In general, both formats use 'standard' PBR rendering, so the idea is the result should look identical in each format. Because of the above, Green -> Roughness and Blue -> Metallic is very much the standard way of setting ORM (Occlusion, Roughness, and Metallic). It is also what is done by Unity for example when exporting to GLTF or USD.

I only point this out as a note that I am not attempting to do something exotic or unusual (which perhaps can be ignored as somewhat of an edge case) but instead am using a well-defined standard which currently Blender doesn't support.

I will try to make a simple test case USD/GLTF file for you.

As a side note, the GLTF specification is a little more rigid for shininess/roughness and metalicity: [https:*www.khronos.org/blog/art-pipeline-for-gltf ](https:*www.khronos.org/blog/art-pipeline-for-gltf) > The Ambient Occlusion, Roughness, and Metallic textures are saved in a single channel-packed texture to reduce the number of texture loads. The textures need to be packed into the channels of your texture as follows: > Red: Ambient Occlusion > **Green: Roughness** > **Blue: Metallic** I appreciate this is GLTF and therefore doesn't apply directly to USD, but at the same time, the formats do sort of go hand-in-hand, ie if you want to author out assets that will be natively consumed on all devices then you have to export to both GLTF and USD. In general, both formats use 'standard' PBR rendering, so the idea is the result should look identical in each format. Because of the above, Green -> Roughness and Blue -> Metallic is very much the standard way of setting ORM (Occlusion, Roughness, and Metallic). It is also what is done by Unity for example when exporting to GLTF or USD. I only point this out as a note that I am not attempting to do something exotic or unusual (which perhaps can be ignored as somewhat of an edge case) but instead am using a well-defined standard which currently Blender doesn't support. I will try to make a simple test case USD/GLTF file for you.
Bastien Montagne commented 2022-04-14 10:08:36 +02:00
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Added subscribers: @makowalski, @mont29

Added subscribers: @makowalski, @mont29
Bastien Montagne commented 2022-04-14 10:08:36 +02:00
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Changed status from 'Needs Developer To Reproduce' to: 'Needs User Info'

Changed status from 'Needs Developer To Reproduce' to: 'Needs User Info'
Bastien Montagne commented 2022-04-14 10:08:36 +02:00
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@scraft Please attach a small reproducible test case, otherwise we'll have to close the report.

@makowalski maybe knows better about this topic though?

@scraft Please attach a small reproducible test case, otherwise we'll have to close the report. @makowalski maybe knows better about this topic though?
Michael Kowalski commented 2022-04-14 17:21:22 +02:00
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I can generate a test case based on the description and will investigate.

I can generate a test case based on the description and will investigate.
Omar Emara commented 2022-06-07 13:16:38 +02:00
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Changed status from 'Needs User Info' to: 'Needs Developer To Reproduce'

Changed status from 'Needs User Info' to: 'Needs Developer To Reproduce'
Bastien Montagne added this to the Pipeline, Assets & IO project 2023-02-09 15:40:38 +01:00
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mikan233 commented 2024-02-01 13:45:10 +01:00
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System Information
Operating system: Windows
Graphics card: NVIDIA GeForce RTX 3070

Blender Version
Broken: 4.0.1, branch: blender-v4.0-release, commit date: 2023-11-16 16:40, hash: d0dd92834a, type: release
Worked: N/A

This problem still exists.


#usda 1.0
(
    endTimeCode = 213
    framesPerSecond = 24
    metersPerUnit = 1
    startTimeCode = 213
    timeCodesPerSecond = 24
    upAxis = "Y"
)

def Cube "cube1" (
    prepend apiSchemas = ["MaterialBindingAPI"]
)
{
    float3[] extent = [(-1, -1, -1), (1, 1, 1)]
    rel material:binding = </mat>
    double size = 2
    matrix4d xformOp:transform = ( (1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (0, 0, 0, 1) )
    uniform token[] xformOpOrder = ["xformOp:transform"]
}

def Material "mat" (
    prepend inherits = </__class_mtl__/usdpreviewmaterial>
)
{
    token outputs:surface.connect = </mat/usdpreviewsurface.outputs:surface>
    matrix4d xformOp:transform = ( (1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (0, 0, 0, 1) )
    uniform token[] xformOpOrder = ["xformOp:transform"]

    def Shader "usdpreviewsurface"
    {
        uniform token info:id = "UsdPreviewSurface"
        color3f inputs:roughness.connect = </mat/usduvtexture1.outputs:r>
        token outputs:surface
    }

    def Shader "usduvtexture1"
    {
        uniform token info:id = "UsdUVTexture"
        asset inputs:file = @testfile.png@
        float2 inputs:st.connect = </mat/usdprimvarreader1.outputs:result>
        float outputs:r
    }

    def Shader "usdprimvarreader1"
    {
        uniform token info:id = "UsdPrimvarReader_float2"
        string inputs:varname = "st"
        float2 outputs:result
    }
}
System Information Operating system: Windows Graphics card: NVIDIA GeForce RTX 3070 Blender Version Broken: 4.0.1, branch: blender-v4.0-release, commit date: 2023-11-16 16:40, hash: d0dd92834a08, type: release Worked: N/A This problem still exists. ``` #usda 1.0 ( endTimeCode = 213 framesPerSecond = 24 metersPerUnit = 1 startTimeCode = 213 timeCodesPerSecond = 24 upAxis = "Y" ) def Cube "cube1" ( prepend apiSchemas = ["MaterialBindingAPI"] ) { float3[] extent = [(-1, -1, -1), (1, 1, 1)] rel material:binding = </mat> double size = 2 matrix4d xformOp:transform = ( (1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (0, 0, 0, 1) ) uniform token[] xformOpOrder = ["xformOp:transform"] } def Material "mat" ( prepend inherits = </__class_mtl__/usdpreviewmaterial> ) { token outputs:surface.connect = </mat/usdpreviewsurface.outputs:surface> matrix4d xformOp:transform = ( (1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (0, 0, 0, 1) ) uniform token[] xformOpOrder = ["xformOp:transform"] def Shader "usdpreviewsurface" { uniform token info:id = "UsdPreviewSurface" color3f inputs:roughness.connect = </mat/usduvtexture1.outputs:r> token outputs:surface } def Shader "usduvtexture1" { uniform token info:id = "UsdUVTexture" asset inputs:file = @testfile.png@ float2 inputs:st.connect = </mat/usdprimvarreader1.outputs:result> float outputs:r } def Shader "usdprimvarreader1" { uniform token info:id = "UsdPrimvarReader_float2" string inputs:varname = "st" float2 outputs:result } } ```
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Iliya Katushenock added
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Iliya Katushenock commented 2024-02-01 14:03:00 +01:00
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Change status to Confirm after 2 years of Needs Info from Developers.

Change status to `Confirm` after 2 years of `Needs Info from Developers`.
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Philipp Oeser commented 2024-02-01 14:24:20 +01:00
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Change status to Confirm after 2 years of Needs Info from Developers.

Em, we still have to reproduce/check on this, will reset to Needs Triage

> Change status to `Confirm` after 2 years of `Needs Info from Developers`. Em, we still have to reproduce/check on this, will reset to `Needs Triage`
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mikan233 commented 2024-02-01 17:12:49 +01:00
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Change status to Confirm after 2 years of Needs Info from Developers.

Em, we still have to reproduce/check on this, will reset to Needs Triage

When use Separate Color / XYZ to connect channels to materials, USD export also not correct.
that can be exported, but the channel is always as 'r'.
img

#usda 1.0
(
    defaultPrim = "Cube"
    doc = "Blender v4.0.1"
    metersPerUnit = 1
    upAxis = "Z"
)

def Xform "Cube"
{
    matrix4d xformOp:transform = ( (1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (0, 0, 0, 1) )
    uniform token[] xformOpOrder = ["xformOp:transform"]

    def Mesh "Cube" (
        prepend apiSchemas = ["MaterialBindingAPI"]
    )
    {
        uniform bool doubleSided = 1
        float3[] extent = [(-1, -1, -1), (1, 1, 1)]
        int[] faceVertexCounts = [4, 4, 4, 4, 4, 4]
        int[] faceVertexIndices = [0, 4, 6, 2, 3, 2, 6, 7, 7, 6, 4, 5, 5, 1, 3, 7, 1, 0, 2, 3, 5, 4, 0, 1]
        rel material:binding = </_materials/Material>
        normal3f[] normals = [(0, 0, 1), (0, 0, 1), (0, 0, 1), (0, 0, 1), (0, -1, 0), (0, -1, 0), (0, -1, 0), (0, -1, 0), (-1, 0, 0), (-1, 0, 0), (-1, 0, 0), (-1, 0, 0), (0, 0, -1), (0, 0, -1), (0, 0, -1), (0, 0, -1), (1, 0, 0), (1, 0, 0), (1, 0, 0), (1, 0, 0), (0, 1, 0), (0, 1, 0), (0, 1, 0), (0, 1, 0)] (
            interpolation = "faceVarying"
        )
        point3f[] points = [(1, 1, 1), (1, 1, -1), (1, -1, 1), (1, -1, -1), (-1, 1, 1), (-1, 1, -1), (-1, -1, 1), (-1, -1, -1)]
        bool[] primvars:sharp_face = [1, 1, 1, 1, 1, 1] (
            interpolation = "uniform"
        )
        texCoord2f[] primvars:UVMap = [(0.625, 0.5), (0.875, 0.5), (0.875, 0.75), (0.625, 0.75), (0.375, 0.75), (0.625, 0.75), (0.625, 1), (0.375, 1), (0.375, 0), (0.625, 0), (0.625, 0.25), (0.375, 0.25), (0.125, 0.5), (0.375, 0.5), (0.375, 0.75), (0.125, 0.75), (0.375, 0.5), (0.625, 0.5), (0.625, 0.75), (0.375, 0.75), (0.375, 0.25), (0.625, 0.25), (0.625, 0.5), (0.375, 0.5)] (
            interpolation = "faceVarying"
        )
        uniform token subdivisionScheme = "none"
    }
}

def "_materials"
{
    def Material "Material"
    {
        token outputs:surface.connect = </_materials/Material/Principled_BSDF.outputs:surface>

        def Shader "Principled_BSDF"
        {
            uniform token info:id = "UsdPreviewSurface"
            float inputs:clearcoat = 0
            float inputs:clearcoatRoughness = 0.03
            color3f inputs:diffuseColor = (0.8, 0.8, 0.8)
            float inputs:ior = 1.45
            float inputs:metallic.connect = </_materials/Material/Image_Texture.outputs:r>
            float inputs:opacity = 1
            float inputs:roughness.connect = </_materials/Material/Image_Texture.outputs:r>
            float inputs:specular = 0.5
            token outputs:surface
        }

        def Shader "Image_Texture"
        {
            uniform token info:id = "UsdUVTexture"
            asset inputs:file = @./textures/CustomUVChecker_byValle_4K.png@
            token inputs:sourceColorSpace = "sRGB"
            float2 inputs:st.connect = </_materials/Material/uvmap.outputs:result>
            float outputs:r
        }

        def Shader "uvmap"
        {
            uniform token info:id = "UsdPrimvarReader_float2"
            token inputs:varname = "UVMap"
            float2 outputs:result
        }
    }
}
> > Change status to `Confirm` after 2 years of `Needs Info from Developers`. > > Em, we still have to reproduce/check on this, will reset to `Needs Triage` When use Separate Color / XYZ to connect channels to materials, USD export also not correct. that can be exported, but the channel is always as 'r'. ![img](https://i.imgur.com/aFtTEcA.jpeg) ``` #usda 1.0 ( defaultPrim = "Cube" doc = "Blender v4.0.1" metersPerUnit = 1 upAxis = "Z" ) def Xform "Cube" { matrix4d xformOp:transform = ( (1, 0, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (0, 0, 0, 1) ) uniform token[] xformOpOrder = ["xformOp:transform"] def Mesh "Cube" ( prepend apiSchemas = ["MaterialBindingAPI"] ) { uniform bool doubleSided = 1 float3[] extent = [(-1, -1, -1), (1, 1, 1)] int[] faceVertexCounts = [4, 4, 4, 4, 4, 4] int[] faceVertexIndices = [0, 4, 6, 2, 3, 2, 6, 7, 7, 6, 4, 5, 5, 1, 3, 7, 1, 0, 2, 3, 5, 4, 0, 1] rel material:binding = </_materials/Material> normal3f[] normals = [(0, 0, 1), (0, 0, 1), (0, 0, 1), (0, 0, 1), (0, -1, 0), (0, -1, 0), (0, -1, 0), (0, -1, 0), (-1, 0, 0), (-1, 0, 0), (-1, 0, 0), (-1, 0, 0), (0, 0, -1), (0, 0, -1), (0, 0, -1), (0, 0, -1), (1, 0, 0), (1, 0, 0), (1, 0, 0), (1, 0, 0), (0, 1, 0), (0, 1, 0), (0, 1, 0), (0, 1, 0)] ( interpolation = "faceVarying" ) point3f[] points = [(1, 1, 1), (1, 1, -1), (1, -1, 1), (1, -1, -1), (-1, 1, 1), (-1, 1, -1), (-1, -1, 1), (-1, -1, -1)] bool[] primvars:sharp_face = [1, 1, 1, 1, 1, 1] ( interpolation = "uniform" ) texCoord2f[] primvars:UVMap = [(0.625, 0.5), (0.875, 0.5), (0.875, 0.75), (0.625, 0.75), (0.375, 0.75), (0.625, 0.75), (0.625, 1), (0.375, 1), (0.375, 0), (0.625, 0), (0.625, 0.25), (0.375, 0.25), (0.125, 0.5), (0.375, 0.5), (0.375, 0.75), (0.125, 0.75), (0.375, 0.5), (0.625, 0.5), (0.625, 0.75), (0.375, 0.75), (0.375, 0.25), (0.625, 0.25), (0.625, 0.5), (0.375, 0.5)] ( interpolation = "faceVarying" ) uniform token subdivisionScheme = "none" } } def "_materials" { def Material "Material" { token outputs:surface.connect = </_materials/Material/Principled_BSDF.outputs:surface> def Shader "Principled_BSDF" { uniform token info:id = "UsdPreviewSurface" float inputs:clearcoat = 0 float inputs:clearcoatRoughness = 0.03 color3f inputs:diffuseColor = (0.8, 0.8, 0.8) float inputs:ior = 1.45 float inputs:metallic.connect = </_materials/Material/Image_Texture.outputs:r> float inputs:opacity = 1 float inputs:roughness.connect = </_materials/Material/Image_Texture.outputs:r> float inputs:specular = 0.5 token outputs:surface } def Shader "Image_Texture" { uniform token info:id = "UsdUVTexture" asset inputs:file = @./textures/CustomUVChecker_byValle_4K.png@ token inputs:sourceColorSpace = "sRGB" float2 inputs:st.connect = </_materials/Material/uvmap.outputs:result> float outputs:r } def Shader "uvmap" { uniform token info:id = "UsdPrimvarReader_float2" token inputs:varname = "UVMap" float2 outputs:result } } } ```
Philipp Oeser commented 2024-02-02 09:55:10 +01:00
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I can confirm the behavior (and sorry this has been lying around in such unclear state for so long).

BUT: this is not really expected to work in the current state of USD import/export, see https://docs.blender.org/manual/en/4.1/files/import_export/usd.html

Not all nodes are supported; currently only Diffuse, Principle, Image Textures, and UVMap nodes are supported.

Also this comment gives a hint at the limitations (this does not mention the channel mapping explicitly, just saying...):

 * Limitations: arbitrary primvar readers or UsdTransform2d not yet
 * supported. For #UsdUVTexture, only the file, st and #sourceColorSpace
 * inputs are handled.
 *
 * TODO(makowalski):  Investigate adding support for converting additional
 * shaders and inputs.  Supporting certain types of inputs, such as texture
 * scale and bias, will probably require creating Blender Group nodes with
 * the corresponding inputs.

Improvements unfortunately only come here bit by bit (e.g. in 925fb66693)

I also understand that you are not doing something out of the ordinary, but uncertain at this point if "Green -> Roughness and Blue -> Metallic is very much the standard way of setting ORM" is something we can always assume, but of course, if this is explicitly specified in the USD file, setting up blenders nodes (via a Separate RGB node) is the way to go.

Maybe @makowalski and/or @CharlesWardlaw can comment on the plans of adding support for more nodes.

That all being said, the issue here is more like a feature request than a "real bug", usually these kinds of reports get closed, but maybe we can keep this as a TODO.

I guess the first (and more straightforward) step would be to tweak the importer (this would just mean adding a single node), the exporter might be a bit more involved (since this would have to traverse all nodes between to target socket and the Image Texture node and the question always is: "what to do if there is additional stuff happening there, not just a channel separation?")

I can confirm the behavior (and sorry this has been lying around in such unclear state for so long). BUT: this is not really expected to work in the current state of USD import/export, see https://docs.blender.org/manual/en/4.1/files/import_export/usd.html >Not all nodes are supported; currently only Diffuse, Principle, Image Textures, and UVMap nodes are supported. Also this comment gives a hint at the limitations (this does not mention the channel mapping explicitly, just saying...): ``` * Limitations: arbitrary primvar readers or UsdTransform2d not yet * supported. For #UsdUVTexture, only the file, st and #sourceColorSpace * inputs are handled. * * TODO(makowalski): Investigate adding support for converting additional * shaders and inputs. Supporting certain types of inputs, such as texture * scale and bias, will probably require creating Blender Group nodes with * the corresponding inputs. ``` Improvements unfortunately only come here bit by bit (e.g. in 925fb66693ded4b8ed03cee86307682f65d6fd8a) I also understand that you are not doing something out of the ordinary, but uncertain at this point if "Green -> Roughness and Blue -> Metallic is very much the standard way of setting ORM" is something we can **always** assume, but of course, if this is explicitly specified in the USD file, setting up blenders nodes (via a `Separate RGB` node) is the way to go. Maybe @makowalski and/or @CharlesWardlaw can comment on the plans of adding support for more nodes. That all being said, the issue here is more like a feature request than a "real bug", usually these kinds of reports get closed, but maybe we can keep this as a TODO. I guess the first (and more straightforward) step would be to tweak the importer (this would just mean adding a single node), the exporter might be a bit more involved (since this would have to traverse all nodes between to target socket and the Image Texture node and the question always is: "what to do if there is additional stuff happening there, not just a channel separation?")
Philipp Oeser commented 2024-02-02 10:03:37 +01:00
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When use Separate Color / XYZ to connect channels to materials, USD export also not correct.
that can be exported, but the channel is always as 'r'.

at the current state, this is also what the code intends to do, see the following comment

/* If the input is a float, we connect it to either the texture alpha or red channels. */

> When use Separate Color / XYZ to connect channels to materials, USD export also not correct. > that can be exported, but the channel is always as 'r'. at the current state, this is also what the code intends to do, see the following comment `/* If the input is a float, we connect it to either the texture alpha or red channels. */`
Philipp Oeser commented 2024-02-02 10:27:22 +01:00
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Actually, I would like to check on this for a bit, maybe it is just a really quick thing to support

Actually, I would like to check on this for a bit, maybe it is just a really quick thing to support
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Philipp Oeser self-assigned this 2024-02-02 10:28:00 +01:00
Philipp Oeser commented 2024-02-02 14:28:37 +01:00
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OK, I got a POC working (both on the export and the import side).

A roundtrip looks like this atm.:

Nodetree that gets exported

image

Nodetree after import

image

So next to testing some more real-world examples, it "just" needs a bit more work to get node placement right and it might make sense to cache the Separate Color nodes as well (so we dont create multiple of these for a single texture).

OK, I got a POC working (both on the export and the import side). A roundtrip looks like this atm.: Nodetree that gets exported ![image](/attachments/4b49cb0e-f61e-4a04-b8e5-48406d0f70c5) Nodetree after import ![image](/attachments/a3385589-3d37-433d-93ea-f18abcef5cc3) So next to testing some more real-world examples, it "just" needs a bit more work to get node placement right and it might make sense to cache the Separate Color nodes as well (so we dont create multiple of these for a single texture).
image.png
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image.png
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Michael Kowalski commented 2024-02-02 18:44:44 +01:00
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@mikan233 @lichtwerk Thanks for following up on this.

My apologies that this issue fell to the wayside. As mentioned above, improvements to the USD Preview Surface IO have been incremental. We've been planning to add support for handling texture channels, but no one has started work on this yet, so this contribution is most welcome.

@lichtwerk Thanks for the prototype! It seems to me you're on the right track. If you'd like to create a pull request with these changes, I would be happy to review it and also discuss further any issues you're encountering.

@mikan233 @lichtwerk Thanks for following up on this. My apologies that this issue fell to the wayside. As mentioned above, improvements to the `USD Preview Surface` IO have been incremental. We've been planning to add support for handling texture channels, but no one has started work on this yet, so this contribution is most welcome. @lichtwerk Thanks for the prototype! It seems to me you're on the right track. If you'd like to create a pull request with these changes, I would be happy to review it and also discuss further any issues you're encountering.
mikan233 commented 2024-02-05 05:50:28 +01:00
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I can confirm the behavior (and sorry this has been lying around in such unclear state for so long).

BUT: this is not really expected to work in the current state of USD import/export, see https://docs.blender.org/manual/en/4.1/files/import_export/usd.html

Not all nodes are supported; currently only Diffuse, Principle, Image Textures, and UVMap nodes are supported.

Also this comment gives a hint at the limitations (this does not mention the channel mapping explicitly, just saying...):

 * Limitations: arbitrary primvar readers or UsdTransform2d not yet
 * supported. For #UsdUVTexture, only the file, st and #sourceColorSpace
 * inputs are handled.
 *
 * TODO(makowalski):  Investigate adding support for converting additional
 * shaders and inputs.  Supporting certain types of inputs, such as texture
 * scale and bias, will probably require creating Blender Group nodes with
 * the corresponding inputs.

Improvements unfortunately only come here bit by bit (e.g. in 925fb66693)

I also understand that you are not doing something out of the ordinary, but uncertain at this point if "Green -> Roughness and Blue -> Metallic is very much the standard way of setting ORM" is something we can always assume, but of course, if this is explicitly specified in the USD file, setting up blenders nodes (via a Separate RGB node) is the way to go.

Maybe @makowalski and/or @CharlesWardlaw can comment on the plans of adding support for more nodes.

That all being said, the issue here is more like a feature request than a "real bug", usually these kinds of reports get closed, but maybe we can keep this as a TODO.

I guess the first (and more straightforward) step would be to tweak the importer (this would just mean adding a single node), the exporter might be a bit more involved (since this would have to traverse all nodes between to target socket and the Image Texture node and the question always is: "what to do if there is additional stuff happening there, not just a channel separation?")

You are right. But the USD specification allows that, Blender to be unable to follow the import and export rules of USD. that be incompatible with most supported software.

> I can confirm the behavior (and sorry this has been lying around in such unclear state for so long). > > BUT: this is not really expected to work in the current state of USD import/export, see https://docs.blender.org/manual/en/4.1/files/import_export/usd.html > > >Not all nodes are supported; currently only Diffuse, Principle, Image Textures, and UVMap nodes are supported. > > Also this comment gives a hint at the limitations (this does not mention the channel mapping explicitly, just saying...): > > ``` > * Limitations: arbitrary primvar readers or UsdTransform2d not yet > * supported. For #UsdUVTexture, only the file, st and #sourceColorSpace > * inputs are handled. > * > * TODO(makowalski): Investigate adding support for converting additional > * shaders and inputs. Supporting certain types of inputs, such as texture > * scale and bias, will probably require creating Blender Group nodes with > * the corresponding inputs. > ``` > > Improvements unfortunately only come here bit by bit (e.g. in 925fb66693ded4b8ed03cee86307682f65d6fd8a) > > I also understand that you are not doing something out of the ordinary, but uncertain at this point if "Green -> Roughness and Blue -> Metallic is very much the standard way of setting ORM" is something we can **always** assume, but of course, if this is explicitly specified in the USD file, setting up blenders nodes (via a `Separate RGB` node) is the way to go. > > Maybe @makowalski and/or @CharlesWardlaw can comment on the plans of adding support for more nodes. > > That all being said, the issue here is more like a feature request than a "real bug", usually these kinds of reports get closed, but maybe we can keep this as a TODO. > > I guess the first (and more straightforward) step would be to tweak the importer (this would just mean adding a single node), the exporter might be a bit more involved (since this would have to traverse all nodes between to target socket and the Image Texture node and the question always is: "what to do if there is additional stuff happening there, not just a channel separation?") You are right. But the USD specification allows that, Blender to be unable to follow the import and export rules of USD. that be incompatible with most supported software.
Philipp Oeser commented 2024-02-06 15:24:33 +01:00
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PR is up , see #117901

PR is up , see https://projects.blender.org/blender/blender/pulls/117901
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