Remove HdStorm-compat option

Recent changes to USD/Storm fix the transparency detection.

src/guc/main.c

@@ -40,13 +40,6 @@ static struct cag_option cmd_options[] = {
     .value_name = NULL,
     .description = "Convert and inline MaterialX materials into the USD layer using UsdMtlx"
   },
-  {
-    .identifier = 'c',
-    .access_letters = "c",
-    .access_name = "hdstorm-compat",
-    .value_name = NULL,
-    .description = "Apply compatibility tweaks for the USD Storm Hydra render delegate"
-  },
   {
     .identifier = 'v',
     .access_letters = "v",
@@ -75,7 +68,6 @@ int main(int argc, char* argv[])
   struct guc_options options = {
     .emit_mtlx = false,
     .mtlx_as_usdshade = false,
-    .hdstorm_compat = false,
     .default_material_variant = 0
   };
 
@@ -91,9 +83,6 @@ int main(int argc, char* argv[])
     case 'u':
       options.mtlx_as_usdshade = true;
       break;
-    case 'c':
-      options.hdstorm_compat = true;
-      break;
     case 'v': {
       const char* value = cag_option_get_value(&context);
       options.default_material_variant = atoi(value); // fall back to 0 on error

src/libguc/include/guc.h

@@ -37,9 +37,6 @@ struct guc_options
   // versions.
   bool mtlx_as_usdshade;
 
-  // Workaround to make hdStorm recognize alpha materials as translucent.
-  bool hdstorm_compat;
-
   // If the asset supports the KHR_materials_variants extension, select the material
   // variant at the given index by default.
   int default_material_variant;

src/libguc/src/converter.cpp

@@ -210,7 +210,7 @@ namespace guc
     , m_stage(stage)
     , m_params(params)
     , m_mtlxDoc(mx::createDocument())
-    , m_mtlxConverter(m_mtlxDoc, m_imgMetadata, params.hdStormCompat)
+    , m_mtlxConverter(m_mtlxDoc, m_imgMetadata)
     , m_usdPreviewSurfaceConverter(m_stage, m_imgMetadata)
   {
   }

src/libguc/src/converter.h

@@ -46,7 +46,6 @@ namespace guc
       bool genRelativePaths;
       bool emitMtlx;
       bool mtlxAsUsdShade;
-      bool hdStormCompat;
       int defaultMaterialVariant;
     };
 

src/libguc/src/fileFormat.cpp

@@ -145,7 +145,6 @@ bool UsdGlTFFileFormat::Read(SdfLayer* layer,
   params.genRelativePaths = false;
   params.emitMtlx = data->emitMtlx;
   params.mtlxAsUsdShade = true;
-  params.hdStormCompat = false;
   params.defaultMaterialVariant = 0;
 
   SdfLayerRefPtr tmpLayer = SdfLayer::CreateAnonymous(".usdc");

src/libguc/src/guc.cpp

@@ -55,7 +55,6 @@ bool convertToUsd(fs::path src_dir,
   params.genRelativePaths = true;
   params.emitMtlx = options->emit_mtlx;
   params.mtlxAsUsdShade = options->mtlx_as_usdshade;
-  params.hdStormCompat = options->hdstorm_compat;
   params.defaultMaterialVariant = options->default_material_variant;
 
   Converter converter(gltf_data, stage, params);

src/libguc/src/materialx.cpp

@@ -267,13 +267,11 @@ namespace detail
 namespace guc
 {
   MaterialXMaterialConverter::MaterialXMaterialConverter(mx::DocumentPtr doc,
-                                                         const ImageMetadataMap& imageMetadataMap,
-                                                         bool hdstorm_compat)
+                                                         const ImageMetadataMap& imageMetadataMap)
     : m_doc(doc)
     , m_imageMetadataMap(imageMetadataMap)
     , m_defaultColorSetName(makeColorSetName(0))
     , m_defaultOpacitySetName(makeOpacitySetName(0))
-    , m_hdstormCompat(hdstorm_compat)
   {
   }
 
@@ -490,20 +488,6 @@ namespace guc
       auto sheenRoughnessFactorDefault = 0.0f; // according to spec
       addFloatTextureInput(nodeGraph, shaderNode, "sheen_roughness", sheen->sheen_roughness_texture, 3, sheen->sheen_roughness_factor, sheenRoughnessFactorDefault);
     }
-
-    // Unfortunately, hdStorm blending is messed up because the material is not flagged as 'translucent':
-    // https://github.com/PixarAnimationStudios/USD/blob/db8e3266dcaa24aa26b7201bc20ff4d8e81448d6/pxr/imaging/hdSt/materialXFilter.cpp#L441-L507
-    // For alpha materials, set a non-zero transmission input to make the renderer believe that we are a translucent Standard Surface.
-    if (material->alpha_mode != cgltf_alpha_mode_opaque && m_hdstormCompat)
-    {
-      mx::InputPtr transmissionInput = material->has_transmission ? shaderNode->getInput("transmission") : shaderNode->addInput("transmission", MTLX_TYPE_FLOAT);
-
-      if (!transmissionInput->hasValue() || (transmissionInput->getValue()->isA<float>() && transmissionInput->getValue()->asA<float>() == 0.0f))
-      {
-        float valueCloseToZero = 0.00001f;
-        transmissionInput->setValue(valueCloseToZero);
-      }
-    }
   }
 
   void MaterialXMaterialConverter::addDiffuseTextureInput(mx::NodeGraphPtr nodeGraph,
@@ -934,18 +918,7 @@ namespace guc
 
     if (texValueType != MTLX_TYPE_FLOAT)
     {
-      bool remapChannelToAlpha = false;
-
-      // USD probably handles greyscale+alpha textures like it does for the UsdPreviewSurface spec:
-      // "If a two-channel texture is fed into a UsdUVTexture, the r, g, and b components of the rgb output will
-      // repeat the first channel's value, while the single a output will be set to the second channel's value."
-      if (m_hdstormCompat)
-      {
-        int channelCount = getTextureChannelCount(textureView);
-        remapChannelToAlpha = (channelCount == 2 && channelIndex == 1);
-      }
-
-      valueNode = detail::makeExtractChannelNode(nodeGraph, valueNode, remapChannelToAlpha ? 3 : channelIndex);
+      valueNode = detail::makeExtractChannelNode(nodeGraph, valueNode, channelIndex);
     }
 
     return valueNode;
@@ -1218,15 +1191,13 @@ namespace guc
 
     int channelCount = metadata.channelCount;
 
-    if (channelCount == 3 || (m_hdstormCompat && channelCount == 1))
+    if (channelCount == 4)
     {
-      // USD promotes single-channel textures to RGB
-      return color ? MTLX_TYPE_COLOR3 : MTLX_TYPE_VECTOR3;
+      return color ? MTLX_TYPE_COLOR4 : MTLX_TYPE_VECTOR4;
     }
-    else if (channelCount == 4 || (m_hdstormCompat && channelCount == 2))
+    else if (channelCount == 3)
     {
-      // And for greyscale-alpha textures, to RGBA (with vec2[1] being alpha)
-      return color ? MTLX_TYPE_COLOR4 : MTLX_TYPE_VECTOR4;
+      return color ? MTLX_TYPE_COLOR3 : MTLX_TYPE_VECTOR3;
     }
     else if (channelCount == 2)
     {

src/libguc/src/materialx.h

@@ -30,8 +30,7 @@ namespace guc
   {
   public:
     MaterialXMaterialConverter(mx::DocumentPtr doc,
-                               const ImageMetadataMap& imageMetadataMap,
-                               bool hdstormCompat);
+                               const ImageMetadataMap& imageMetadataMap);
 
     void convert(const cgltf_material* material, const std::string& materialName);
 
@@ -41,8 +40,6 @@ namespace guc
     std::string m_defaultColorSetName;
     std::string m_defaultOpacitySetName;
 
-    bool m_hdstormCompat;
-
   private:
     void createUnlitSurfaceNodes(const cgltf_material* material,
                                  const std::string& materialName);