Fix #106326: Add scale-bias processing for UsdUVTexture #115224

Jesse Yurkovich · 2023-11-21T08:14:33+01:00

Jesse Yurkovich commented

2023-11-21 08:14:33 +01:00

This adds the processing required to import and export, simple, material
graphs utilizing the UsdUVTexture Scale and Bias inputs.

Since Blender does not have equivalent inputs on its Image node, a
Multiply-Add node is used instead. This matches the calculation as per
the UsdPreviewSurface spec[1]

A complicating factor here is when these two inputs are used for normal
map textures. The Scale and Bias inputs are authored in such a way to
take the [0, 1] image data and expand into the [-1, 1] tangent space
range as per the spec. However, the Blender Normal Map node expects to
do this transformation itself. The processing in this patch needs to
account for this. For the case of normal maps it will:

Apply the Scale-Bias calculation directly as authored
Apply an additional transform to move from [-1, 1] back into [0, 1]
Feeds this into the Normal Map node

This processing extends to Export as well. During material graph
traversal we need to "skip" the middle adjustment transform and only
export the "real" Scale-Bias data. Traversing the graph like this can be
error prone but is probably the best we can do without having a native
Scale-Bias concept on Blender's Image node.

[1] https://openusd.org/release/spec_usdpreviewsurface.html#texture-reader

Testing performed

The test case in #106326 will load correctly and can be round-tripped as well (both EEVEE and Cycles seem ok)
Spot checked that some ALab and Intel Moore Lane assets still load correctly

Here is what the 3 graphs from the above issue look like. Notice that the "easy"/"default" case of Scale=(2, 2, 2), Bias=(-1, -1, -1) will yield no additional nodes:

This adds the processing required to import and export, simple, material graphs utilizing the UsdUVTexture Scale and Bias inputs. Since Blender does not have equivalent inputs on its Image node, a Multiply-Add node is used instead. This matches the calculation as per the UsdPreviewSurface spec[1] A complicating factor here is when these two inputs are used for normal map textures. The Scale and Bias inputs are authored in such a way to take the [0, 1] image data and expand into the [-1, 1] tangent space range as per the spec. However, the Blender Normal Map node expects to do this transformation itself. The processing in this patch needs to account for this. For the case of normal maps it will: - Apply the Scale-Bias calculation directly as authored - Apply an additional transform to move from [-1, 1] back into [0, 1] - Feeds this into the Normal Map node This processing extends to Export as well. During material graph traversal we need to "skip" the middle adjustment transform and only export the "real" Scale-Bias data. Traversing the graph like this can be error prone but is probably the best we can do without having a native Scale-Bias concept on Blender's Image node. [1] https://openusd.org/release/spec_usdpreviewsurface.html#texture-reader ---- Testing performed - The test case in #106326 will load correctly and can be round-tripped as well (both EEVEE and Cycles seem ok) - Spot checked that some ALab and Intel Moore Lane assets still load correctly Here is what the 3 graphs from the above issue look like. Notice that the "easy"/"default" case of Scale=(2, 2, 2), Bias=(-1, -1, -1) will yield no additional nodes: ![example.png](/attachments/b3f76251-7609-4289-a47d-d1ddc4965e51)

example.png

926 KiB

Jesse Yurkovich added 1 commit 2023-11-21 08:14:44 +01:00

d394ac7a5e USD: Add scale-bias processing for UsdUVTexture

Jesse Yurkovich requested review from Charles Wardlaw 2023-11-21 08:16:19 +01:00

Jesse Yurkovich requested review from Michael Kowalski 2023-11-21 08:16:19 +01:00

Jesse Yurkovich added the

 @ -586,0 +591,4 @@
   const char *sock_output_name;
 };
 IntermediateNode add_normal_map(const pxr::UsdShadeShader &usd_shader,

 @ -586,0 +663,4 @@
   return scale_bias;
 }
 IntermediateNode add_scale_bias_adjust(bNodeTree *ntree, int column, NodePlacementContext *r_ctx)

 @ -236,0 +262,4 @@
           if (!scale_attr) {
             scale_attr = usd_shader.CreateInput(usdtokens::scale, pxr::SdfValueTypeNames->Float4);
           }
           scale_attr.Set(pxr::VtValue(scale));

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Fix #106326: Add scale-bias processing for UsdUVTexture #115224