Added support for KHR_materials_emissive_strength

according to spec https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos/KHR_materials_emissive_strength

code/AssetLib/glTF2/glTF2Asset.h

@@ -51,6 +51,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *   KHR_materials_transmission full
  *   KHR_materials_volume full
  *   KHR_materials_ior full
+ *   KHR_materials_emissive_strength full
  */
 #ifndef GLTF2ASSET_H_INC
 #define GLTF2ASSET_H_INC
@@ -801,6 +802,13 @@ struct MaterialIOR {
     void SetDefaults();
 };
 
+struct MaterialEmissiveStrength {
+    float emissiveStrength = 0.f;
+
+    MaterialEmissiveStrength() { SetDefaults(); }
+    void SetDefaults();
+};
+
 //! The material appearance of a primitive.
 struct Material : public Object {
     //PBR metallic roughness properties
@@ -833,6 +841,9 @@ struct Material : public Object {
     //extension: KHR_materials_ior
     Nullable<MaterialIOR> materialIOR;
     
+	//extension: KHR_materials_emissive_strength
+    Nullable<MaterialEmissiveStrength> materialEmissiveStrength;
+
     //extension: KHR_materials_unlit
     bool unlit;
 
@@ -1106,6 +1117,7 @@ public:
         bool KHR_materials_transmission;
         bool KHR_materials_volume;
         bool KHR_materials_ior;
+		bool KHR_materials_emissive_strength;
         bool KHR_draco_mesh_compression;
         bool FB_ngon_encoding;
         bool KHR_texture_basisu;
@@ -1120,6 +1132,7 @@ public:
                 KHR_materials_transmission(false), 
                 KHR_materials_volume(false),
                 KHR_materials_ior(false),
+				KHR_materials_emissive_strength(false),
                 KHR_draco_mesh_compression(false),
                 FB_ngon_encoding(false),
                 KHR_texture_basisu(false) {

code/AssetLib/glTF2/glTF2Asset.inl

@@ -1313,6 +1313,16 @@ inline void Material::Read(Value &material, Asset &r) {
             }
         }
 
+		if (r.extensionsUsed.KHR_materials_emissive_strength) {
+            if (Value *curMaterialEmissiveStrength = FindObject(*extensions, "KHR_materials_emissive_strength")) {
+                MaterialEmissiveStrength emissiveStrength;
+
+                ReadMember(*curMaterialEmissiveStrength, "emissiveStrength", emissiveStrength.emissiveStrength);
+
+                this->materialEmissiveStrength = Nullable<MaterialEmissiveStrength>(emissiveStrength);
+            }
+        }
+
         unlit = nullptr != FindObject(*extensions, "KHR_materials_unlit");
     }
 }
@@ -1355,6 +1365,11 @@ inline void MaterialIOR::SetDefaults() {
     ior = 1.5f;
 }
 
+inline void MaterialEmissiveStrength::SetDefaults() {
+    //KHR_materials_emissive_strength properties
+    emissiveStrength = 0.f;
+}
+
 inline void Mesh::Read(Value &pJSON_Object, Asset &pAsset_Root) {
     Value *curName = FindMember(pJSON_Object, "name");
     if (nullptr != curName && curName->IsString()) {
@@ -2026,6 +2041,7 @@ inline void Asset::ReadExtensionsUsed(Document &doc) {
     CHECK_EXT(KHR_materials_transmission);
     CHECK_EXT(KHR_materials_volume);
     CHECK_EXT(KHR_materials_ior);
+	CHECK_EXT(KHR_materials_emissive_strength);
     CHECK_EXT(KHR_draco_mesh_compression);
     CHECK_EXT(KHR_texture_basisu);
 

code/AssetLib/glTF2/glTF2AssetWriter.h

@@ -51,6 +51,7 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *   KHR_materials_transmission: full
  *   KHR_materials_volume: full
  *   KHR_materials_ior: full
+ *   KHR_materials_emissive_strength: full
  */
 #ifndef GLTF2ASSETWRITER_H_INC
 #define GLTF2ASSETWRITER_H_INC

code/AssetLib/glTF2/glTF2AssetWriter.inl

@@ -511,6 +511,20 @@ namespace glTF2 {
             }
         }
 
+		if (m.materialEmissiveStrength.isPresent) {
+            Value materialEmissiveStrength(rapidjson::Type::kObjectType);
+
+            MaterialEmissiveStrength &emissiveStrength = m.materialEmissiveStrength.value;
+
+            if (emissiveStrength.emissiveStrength != 0.f) {
+                WriteFloat(materialEmissiveStrength, emissiveStrength.emissiveStrength, "emissiveStrength", w.mAl);
+            }
+
+            if (!emissiveStrength.ObjectEmpty()) {
+                exts.AddMember("KHR_materials_emissive_strength", emissiveStrength, w.mAl);
+            }
+        }
+
         if (!exts.ObjectEmpty()) {
             obj.AddMember("extensions", exts, w.mAl);
         }
@@ -935,6 +949,10 @@ namespace glTF2 {
                 exts.PushBack(StringRef("KHR_materials_ior"), mAl);
             }
 
+			if (this->mAsset.extensionsUsed.KHR_materials_emissive_strength) {
+                exts.PushBack(StringRef("KHR_materials_emissive_strength"), mAl);
+            }
+
             if (this->mAsset.extensionsUsed.FB_ngon_encoding) {
                 exts.PushBack(StringRef("FB_ngon_encoding"), mAl);
             }

code/AssetLib/glTF2/glTF2Exporter.cpp

@@ -733,6 +733,10 @@ bool glTF2Exporter::GetMatIOR(const aiMaterial &mat, glTF2::MaterialIOR &ior) {
     return mat.Get(AI_MATKEY_REFRACTI, ior.ior) == aiReturn_SUCCESS;
 }
 
+bool glTF2Exporter::GetMatEmissiveStrength(const aiMaterial &mat, glTF2::MaterialEmissiveStrength &emissiveStrength) {
+    return mat.Get(AI_MATKEY_EMISSIVE_INTENSITY, emissiveStrength.emissiveStrength) == aiReturn_SUCCESS;
+}
+
 void glTF2Exporter::ExportMaterials() {
     aiString aiName;
     for (unsigned int i = 0; i < mScene->mNumMaterials; ++i) {
@@ -862,6 +866,12 @@ void glTF2Exporter::ExportMaterials() {
                 if (GetMatIOR(mat, ior)) {
                     mAsset->extensionsUsed.KHR_materials_ior = true;
                     m->materialIOR = Nullable<MaterialIOR>(ior);
+                }
+				
+				MaterialEmissiveStrength emissiveStrength;
+                if (GetMatEmissiveStrength(mat, emissiveStrength)) {
+                    mAsset->extensionsUsed.KHR_materials_emissive_strength = true;
+                    m->materialEmissiveStrength = Nullable<MaterialEmissiveStrength>(emissiveStrength);
                 }
             }
         }

code/AssetLib/glTF2/glTF2Exporter.h

@@ -81,6 +81,7 @@ struct MaterialClearcoat;
 struct MaterialTransmission;
 struct MaterialVolume;
 struct MaterialIOR;
+struct MaterialEmissiveStrength;
 
 // Vec/matrix types, as raw float arrays
 typedef float(vec2)[2];
@@ -121,6 +122,7 @@ protected:
     bool GetMatTransmission(const aiMaterial &mat, glTF2::MaterialTransmission &transmission);
     bool GetMatVolume(const aiMaterial &mat, glTF2::MaterialVolume &volume);
     bool GetMatIOR(const aiMaterial &mat, glTF2::MaterialIOR &ior);
+	bool GetMatEmissiveStrength(const aiMaterial &mat, glTF2::MaterialEmissiveStrength &emissiveStrength);
     void ExportMetadata();
     void ExportMaterials();
     void ExportMeshes();

code/AssetLib/glTF2/glTF2Importer.cpp

@@ -357,6 +357,13 @@ static aiMaterial *ImportMaterial(std::vector<int> &embeddedTexIdxs, Asset &r, M
             aimat->AddProperty(&ior.ior, 1, AI_MATKEY_REFRACTI);
         }
 
+		// KHR_materials_emissive_strength
+        if (mat.materialEmissiveStrength.isPresent) {
+            MaterialEmissiveStrength &emissiveStrength = mat.materialEmissiveStrength.value;
+
+            aimat->AddProperty(&emissiveStrength.emissiveStrength, 1, AI_MATKEY_EMISSIVE_INTENSITY);
+        }
+
         return aimat;
     } catch (...) {
         delete aimat;