AssetLoader: expose reusable GLTF material loading

Move the material loading context and conversion helper into the public GLTF
loader API so clients can build GLTF::Material objects without constructing a
GLTF::Model.

Author: TheMostDiligent

AssetLoader/interface/GLTFDocument.hpp

@@ -138,6 +138,9 @@ class Document
     /// Returns the number of textures in the document.
     Uint32 GetTextureCount() const;
 
+    /// Returns the number of materials in the document.
+    Uint32 GetMaterialCount() const;
+
     /// Resolves a GLTF texture to either an external URI or an embedded encoded-data span.
     ///
     /// Embedded buffer-view spans are owned by the document buffers. Embedded data URI

AssetLoader/interface/GLTFLoader.hpp

@@ -149,6 +149,19 @@ static constexpr std::array<TextureAttributeDesc, 17> DefaultTextureAttributes =
 };
 // clang-format on
 
+/// Material loading context.
+struct MaterialLoadContext
+{
+    const TextureAttributeDesc* TextureAttributes    = DefaultTextureAttributes.data();
+    Uint32                      NumTextureAttributes = static_cast<Uint32>(DefaultTextureAttributes.size());
+
+    const TextureAttributeDesc& GetTextureAttribute(size_t Idx) const;
+
+    /// Returns the material texture attribute index in Material.ShaderAttribs for
+    /// the given texture attribute name, or -1 if the attribute is not defined.
+    int GetTextureAttributeIndex(const char* Name) const;
+};
+
 
 struct Material
 {
@@ -410,6 +423,16 @@ struct Material
     }
 };
 
+/// Converts a tinygltf material to GLTF::Material.
+Material LoadMaterial(const tinygltf::Model&     GltfModel,
+                      const tinygltf::Material&  GltfMaterial,
+                      const MaterialLoadContext& LoadCtx = {});
+
+/// Loads a material by index from a GLTF document.
+Material LoadMaterial(const Document&            GltfDoc,
+                      Uint32                     MaterialIndex,
+                      const MaterialLoadContext& LoadCtx = {});
+
 
 struct Primitive
 {

AssetLoader/src/GLTFDocument.cpp

@@ -130,6 +130,14 @@ Uint32 Document::GetTextureCount() const
     return static_cast<Uint32>(gltf_model.textures.size());
 }
 
+Uint32 Document::GetMaterialCount() const
+{
+    const tinygltf::Model& gltf_model = GetModel();
+    DEV_CHECK_ERR(gltf_model.materials.size() <= (std::numeric_limits<Uint32>::max)(),
+                  "Too many materials in GLTF document");
+    return static_cast<Uint32>(gltf_model.materials.size());
+}
+
 bool Document::GetTextureSourceInfo(Uint32 TextureIndex, TextureSourceInfo& Source) const
 {
     const tinygltf::Model& gltf_model = GetModel();

AssetLoader/src/GLTFLoader.cpp

@@ -318,6 +318,18 @@ static int GetTextureAttributeIndexFromArray(const TextureAttributeDesc* pTextur
 
 } // namespace
 
+const TextureAttributeDesc& MaterialLoadContext::GetTextureAttribute(size_t Idx) const
+{
+    VERIFY_EXPR(TextureAttributes != nullptr);
+    VERIFY_EXPR(Idx < NumTextureAttributes);
+    return TextureAttributes[Idx];
+}
+
+int MaterialLoadContext::GetTextureAttributeIndex(const char* Name) const
+{
+    return GetTextureAttributeIndexFromArray(TextureAttributes, NumTextureAttributes, Name);
+}
+
 Model::Model(const ModelCreateInfo& CI)
 {
     DEV_CHECK_ERR(CI.IndexType == VT_UINT16 || CI.IndexType == VT_UINT32, "Invalid index type");
@@ -1240,24 +1252,6 @@ static void SetMaterialTextureSamplerProps(const tinygltf::Model& gltf_model, in
     Attribs.SetWrapVMode(GltfWrapModeToAddressMode(gltf_sampler.wrapT));
 }
 
-struct MaterialLoadContext
-{
-    const TextureAttributeDesc* TextureAttributes    = nullptr;
-    Uint32                      NumTextureAttributes = 0;
-
-    const TextureAttributeDesc& GetTextureAttribute(size_t Idx) const
-    {
-        VERIFY_EXPR(TextureAttributes != nullptr);
-        VERIFY_EXPR(Idx < NumTextureAttributes);
-        return TextureAttributes[Idx];
-    }
-
-    int GetTextureAttributeIndex(const char* Name) const
-    {
-        return GetTextureAttributeIndexFromArray(TextureAttributes, NumTextureAttributes, Name);
-    }
-};
-
 static void ReadKhrTextureTransform(const MaterialLoadContext&    LoadCtx,
                                     const tinygltf::ExtensionMap& Extensions,
                                     MaterialBuilder&              Mat,
@@ -1405,9 +1399,9 @@ static void LoadExtensionParameter(const tinygltf::Value& Ext, const char* Name,
     }
 }
 
-static Material LoadMaterial(const tinygltf::Model&     gltf_model,
-                             const tinygltf::Material&  gltf_mat,
-                             const MaterialLoadContext& LoadCtx)
+Material LoadMaterial(const tinygltf::Model&     gltf_model,
+                      const tinygltf::Material&  gltf_mat,
+                      const MaterialLoadContext& LoadCtx)
 {
     Material        Mat;
     MaterialBuilder MatBuilder{Mat};
@@ -1655,6 +1649,20 @@ static Material LoadMaterial(const tinygltf::Model&     gltf_model,
     return Mat;
 }
 
+Material LoadMaterial(const Document&            GltfDoc,
+                      Uint32                     MaterialIndex,
+                      const MaterialLoadContext& LoadCtx)
+{
+    const tinygltf::Model& gltf_model = GltfDoc.GetModel();
+    if (MaterialIndex >= gltf_model.materials.size())
+    {
+        UNEXPECTED("Material index is out of range");
+        return {};
+    }
+
+    return LoadMaterial(gltf_model, gltf_model.materials[MaterialIndex], LoadCtx);
+}
+
 void Model::LoadMaterials(const tinygltf::Model& gltf_model, const ModelCreateInfo::MaterialLoadCallbackType& MaterialLoadCallback)
 {
     const MaterialLoadContext LoadCtx{