Added GLTF Extension KHR_materials_anisotropy (#5950)

* added gltf extension KHR_materials_anisotropy

* Update glTF2Importer.cpp

---------

Co-authored-by: lutz.hoeren <[email protected]>
Co-authored-by: Kim Kulling <[email protected]>

code/AssetLib/glTF2/glTF2Asset.h

@@ -53,6 +53,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *   KHR_materials_volume full
  *   KHR_materials_ior full
  *   KHR_materials_emissive_strength full
+ *   KHR_materials_anisotropy full
  */
 #ifndef GLTF2ASSET_H_INC
 #define GLTF2ASSET_H_INC
@@ -821,6 +822,15 @@ struct MaterialEmissiveStrength {
     void SetDefaults();
 };
 
+struct MaterialAnisotropy {
+    float anisotropyStrength = 0.f;
+    float anisotropyRotation = 0.f;
+    TextureInfo anisotropyTexture;
+
+    MaterialAnisotropy() { SetDefaults(); }
+    void SetDefaults();
+};
+
 //! The material appearance of a primitive.
 struct Material : public Object {
     //PBR metallic roughness properties
@@ -859,6 +869,9 @@ struct Material : public Object {
     //extension: KHR_materials_emissive_strength
     Nullable<MaterialEmissiveStrength> materialEmissiveStrength;
 
+    //extension: KHR_materials_anisotropy
+    Nullable<MaterialAnisotropy> materialAnisotropy;
+
     //extension: KHR_materials_unlit
     bool unlit;
 
@@ -1133,6 +1146,7 @@ public:
         bool KHR_materials_volume;
         bool KHR_materials_ior;
         bool KHR_materials_emissive_strength;
+        bool KHR_materials_anisotropy;
         bool KHR_draco_mesh_compression;
         bool FB_ngon_encoding;
         bool KHR_texture_basisu;
@@ -1149,6 +1163,7 @@ public:
                 KHR_materials_volume(false),
                 KHR_materials_ior(false),
                 KHR_materials_emissive_strength(false),
+                KHR_materials_anisotropy(false),
                 KHR_draco_mesh_compression(false),
                 FB_ngon_encoding(false),
                 KHR_texture_basisu(false) {

code/AssetLib/glTF2/glTF2Asset.inl

@@ -1403,6 +1403,18 @@ inline void Material::Read(Value &material, Asset &r) {
             }
         }
 
+        if (r.extensionsUsed.KHR_materials_anisotropy) {
+            if (Value *curMaterialAnisotropy = FindObject(*extensions, "KHR_materials_anisotropy")) {
+                MaterialAnisotropy anisotropy;
+
+                ReadMember(*curMaterialAnisotropy, "anisotropyStrength", anisotropy.anisotropyStrength);
+                ReadMember(*curMaterialAnisotropy, "anisotropyRotation", anisotropy.anisotropyRotation);
+                ReadTextureProperty(r, *curMaterialAnisotropy, "anisotropyTexture", anisotropy.anisotropyTexture);
+
+                this->materialAnisotropy = Nullable<MaterialAnisotropy>(anisotropy);
+            }
+        }
+
         unlit = nullptr != FindObject(*extensions, "KHR_materials_unlit");
     }
 }
@@ -1456,6 +1468,12 @@ inline void MaterialEmissiveStrength::SetDefaults() {
     emissiveStrength = 0.f;
 }
 
+inline void MaterialAnisotropy::SetDefaults() {
+    //KHR_materials_anisotropy properties
+    anisotropyStrength = 0.f;
+    anisotropyRotation = 0.f;
+}
+
 inline void Mesh::Read(Value &pJSON_Object, Asset &pAsset_Root) {
     Value *curName = FindMember(pJSON_Object, "name");
     if (nullptr != curName && curName->IsString()) {
@@ -2153,6 +2171,7 @@ inline void Asset::ReadExtensionsUsed(Document &doc) {
     CHECK_EXT(KHR_materials_volume);
     CHECK_EXT(KHR_materials_ior);
     CHECK_EXT(KHR_materials_emissive_strength);
+    CHECK_EXT(KHR_materials_anisotropy);
     CHECK_EXT(KHR_draco_mesh_compression);
     CHECK_EXT(KHR_texture_basisu);
 

code/AssetLib/glTF2/glTF2AssetWriter.h

@@ -53,6 +53,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *   KHR_materials_volume: full
  *   KHR_materials_ior: full
  *   KHR_materials_emissive_strength: full
+ *   KHR_materials_anisotropy: full
  */
 #ifndef GLTF2ASSETWRITER_H_INC
 #define GLTF2ASSETWRITER_H_INC

code/AssetLib/glTF2/glTF2AssetWriter.inl

@@ -546,6 +546,26 @@ namespace glTF2 {
             }
         }
 
+        if (m.materialAnisotropy.isPresent) {
+            Value materialAnisotropy(rapidjson::Type::kObjectType);
+
+            MaterialAnisotropy &anisotropy = m.materialAnisotropy.value;
+
+            if (anisotropy.anisotropyStrength != 0.f) {
+                WriteFloat(materialAnisotropy, anisotropy.anisotropyStrength, "anisotropyStrength", w.mAl);
+            }
+
+            if (anisotropy.anisotropyRotation != 0.f) {
+                WriteFloat(materialAnisotropy, anisotropy.anisotropyRotation, "anisotropyRotation", w.mAl);
+            }
+
+            WriteTex(materialAnisotropy, anisotropy.anisotropyTexture, "anisotropyTexture", w.mAl);
+
+            if (!materialAnisotropy.ObjectEmpty()) {
+                exts.AddMember("KHR_materials_anisotropy", materialAnisotropy, w.mAl);
+            }
+        }
+
         if (!exts.ObjectEmpty()) {
             obj.AddMember("extensions", exts, w.mAl);
         }
@@ -1018,6 +1038,10 @@ namespace glTF2 {
                 exts.PushBack(StringRef("KHR_materials_emissive_strength"), mAl);
             }
 
+            if (this->mAsset.extensionsUsed.KHR_materials_anisotropy) {
+                exts.PushBack(StringRef("KHR_materials_anisotropy"), mAl);
+            }
+
             if (this->mAsset.extensionsUsed.FB_ngon_encoding) {
                 exts.PushBack(StringRef("FB_ngon_encoding"), mAl);
             }

code/AssetLib/glTF2/glTF2Exporter.cpp

@@ -804,6 +804,22 @@ bool glTF2Exporter::GetMatEmissiveStrength(const aiMaterial &mat, glTF2::Materia
     return mat.Get(AI_MATKEY_EMISSIVE_INTENSITY, emissiveStrength.emissiveStrength) == aiReturn_SUCCESS;
 }
 
+bool glTF2Exporter::GetMatAnisotropy(const aiMaterial &mat, glTF2::MaterialAnisotropy &anisotropy) {
+    if (mat.Get(AI_MATKEY_ANISOTROPY_FACTOR, anisotropy.anisotropyStrength) != aiReturn_SUCCESS) {
+        return false;
+    }
+
+    // do not export anisotropy when strength is zero
+    if (anisotropy.anisotropyStrength == 0.0f) {
+        return false;
+    }
+
+    mat.Get(AI_MATKEY_ANISOTROPY_ROTATION, anisotropy.anisotropyRotation);
+    GetMatTex(mat, anisotropy.anisotropyTexture, AI_MATKEY_ANISOTROPY_TEXTURE);
+
+    return true;
+}
+
 void glTF2Exporter::ExportMaterials() {
     aiString aiName;
     for (unsigned int i = 0; i < mScene->mNumMaterials; ++i) {
@@ -956,6 +972,12 @@ void glTF2Exporter::ExportMaterials() {
                     mAsset->extensionsUsed.KHR_materials_emissive_strength = true;
                     m->materialEmissiveStrength = Nullable<MaterialEmissiveStrength>(emissiveStrength);
                 }
+
+                MaterialAnisotropy anisotropy;
+                if (GetMatAnisotropy(mat, anisotropy)) {
+                    mAsset->extensionsUsed.KHR_materials_anisotropy = true;
+                    m->materialAnisotropy = Nullable<MaterialAnisotropy>(anisotropy);
+                }
             }
         }
     }

code/AssetLib/glTF2/glTF2Exporter.h

@@ -84,6 +84,7 @@ struct MaterialTransmission;
 struct MaterialVolume;
 struct MaterialIOR;
 struct MaterialEmissiveStrength;
+struct MaterialAnisotropy;
 
 // Vec/matrix types, as raw float arrays
 typedef float(vec2)[2];
@@ -126,6 +127,7 @@ protected:
     bool GetMatVolume(const aiMaterial &mat, glTF2::MaterialVolume &volume);
     bool GetMatIOR(const aiMaterial &mat, glTF2::MaterialIOR &ior);
     bool GetMatEmissiveStrength(const aiMaterial &mat, glTF2::MaterialEmissiveStrength &emissiveStrength);
+    bool GetMatAnisotropy(const aiMaterial &mat, glTF2::MaterialAnisotropy &anisotropy);
     void ExportMetadata();
     void ExportMaterials();
     void ExportMeshes();

code/AssetLib/glTF2/glTF2Importer.cpp

@@ -2,7 +2,7 @@
 Open Asset Import Library (assimp)
 ----------------------------------------------------------------------
 
-Copyright (c) 2006-2024, assimp team
+Copyright (c) 2006-2025, assimp team
 
 All rights reserved.
 
@@ -71,6 +71,7 @@ using namespace glTF2;
 using namespace glTFCommon;
 
 namespace {
+
 // generate bi-tangents from normals and tangents according to spec
 struct Tangent {
     aiVector3D xyz;
@@ -369,11 +370,21 @@ static aiMaterial *ImportMaterial(std::vector<int> &embeddedTexIdxs, Asset &r, M
 
         // KHR_materials_emissive_strength
         if (mat.materialEmissiveStrength.isPresent) {
-            MaterialEmissiveStrength &emissiveStrength = mat.materialEmissiveStrength.value;
+            const MaterialEmissiveStrength &emissiveStrength = mat.materialEmissiveStrength.value;
 
             aimat->AddProperty(&emissiveStrength.emissiveStrength, 1, AI_MATKEY_EMISSIVE_INTENSITY);
         }
 
+        // KHR_materials_anisotropy
+        if (mat.materialAnisotropy.isPresent) {
+            const MaterialAnisotropy &anisotropy = mat.materialAnisotropy.value;
+
+            aimat->AddProperty(&anisotropy.anisotropyStrength, 1, AI_MATKEY_ANISOTROPY_FACTOR);
+            aimat->AddProperty(&anisotropy.anisotropyRotation, 1, AI_MATKEY_ANISOTROPY_ROTATION);
+
+            SetMaterialTextureProperty(embeddedTexIdxs, r, anisotropy.anisotropyTexture, aimat, AI_MATKEY_ANISOTROPY_TEXTURE);
+        }
+
         return aimat;
     } catch (...) {
         delete aimat;

include/assimp/material.h

@@ -334,12 +334,17 @@ enum aiTextureType {
     aiTextureType_MAYA_SPECULAR_COLOR = 24,
     aiTextureType_MAYA_SPECULAR_ROUGHNESS = 25,
 
+    /** Anisotropy
+    * Simulates a surface with directional properties
+    */
+    aiTextureType_ANISOTROPY = 26,
+
 #ifndef SWIG
     _aiTextureType_Force32Bit = INT_MAX
 #endif
 };
 
-#define AI_TEXTURE_TYPE_MAX aiTextureType_MAYA_SPECULAR_ROUGHNESS
+#define AI_TEXTURE_TYPE_MAX aiTextureType_ANISOTROPY
 
 // -------------------------------------------------------------------------------
 /**
@@ -1073,6 +1078,11 @@ extern "C" {
 #define AI_MATKEY_EMISSIVE_INTENSITY "$mat.emissiveIntensity", 0, 0
 #define AI_MATKEY_USE_AO_MAP         "$mat.useAOMap", 0, 0
 
+// Anisotropy
+// ----------
+#define AI_MATKEY_ANISOTROPY_ROTATION "$mat.anisotropyRotation", 0, 0
+#define AI_MATKEY_ANISOTROPY_TEXTURE aiTextureType_ANISOTROPY, 0
+
 // ---------------------------------------------------------------------------
 // Pure key names for all texture-related properties
 //! @cond MATS_DOC_FULL

test/unit/utMaterialSystem.cpp

@@ -267,6 +267,7 @@ TEST_F(MaterialSystemTest, testMaterialTextureTypeEnum) {
         case aiTextureType_SHEEN:
         case aiTextureType_CLEARCOAT:
         case aiTextureType_TRANSMISSION:
+        case aiTextureType_ANISOTROPY:
         case aiTextureType_UNKNOWN:
             if (i > maxTextureType)
                 maxTextureType = i;