SpecularFactor import and export improvements

The changes here (which only apply to reading from or writing to pbrSpecularGlossiness) will:

- store and read specular color on `AI_MATKEY_COLOR_SPECULAR ` rather than `AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS_SPECULAR_FACTOR`
- store and read specular texture from `aiTextureType_SPECULAR` rather than `AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS_SPECULARGLOSSINESS_TEXTURE`. Even though pbrSG’s specularGlossiness texture uses the alpha channel for glossiness, it will still work well enough with just the RGB channels of the image

code/glTF2Asset.h

@@ -172,9 +172,7 @@ namespace glTF2
 	#define AI_MATKEY_GLTF_ALPHAMODE "$mat.gltf.alphaMode", 0, 0
 	#define AI_MATKEY_GLTF_ALPHACUTOFF "$mat.gltf.alphaCutoff", 0, 0
 	#define AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS "$mat.gltf.pbrSpecularGlossiness", 0, 0
-	#define AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS_SPECULAR_FACTOR "$clr.specular", 0, 1
 	#define AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS_GLOSSINESS_FACTOR "$mat.gltf.pbrMetallicRoughness.glossinessFactor", 0, 0
-	#define AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS_SPECULARGLOSSINESS_TEXTURE aiTextureType_UNKNOWN, 1
 
 	#define _AI_MATKEY_GLTF_TEXTURE_TEXCOORD_BASE "$tex.file.texCoord"
 	#define _AI_MATKEY_GLTF_MAPPINGNAME_BASE "$tex.mappingname"

code/glTF2Exporter.cpp

@@ -470,11 +470,11 @@ void glTF2Exporter::ExportMaterials()
 
             PbrSpecularGlossiness pbrSG;
 
-            GetMatColor(mat, pbrSG.specularFactor, AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS_SPECULAR_FACTOR);
             mat->Get(AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS_GLOSSINESS_FACTOR, pbrSG.glossinessFactor);
-            GetMatTex(mat, pbrSG.specularGlossinessTexture, AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS_SPECULARGLOSSINESS_TEXTURE);
             GetMatColor(mat, pbrSG.diffuseFactor, AI_MATKEY_COLOR_DIFFUSE);
+            GetMatColor(mat, pbrSG.specularFactor, AI_MATKEY_COLOR_SPECULAR);
             GetMatTex(mat, pbrSG.diffuseTexture, aiTextureType_DIFFUSE);
+            GetMatTex(mat, pbrSG.specularGlossinessTexture, aiTextureType_SPECULAR);
 
             m->pbrSpecularGlossiness = Nullable<PbrSpecularGlossiness>(pbrSG);
         }

code/glTF2Importer.cpp

@@ -253,11 +253,13 @@ void glTF2Importer::ImportMaterials(glTF2::Asset& r)
             PbrSpecularGlossiness &pbrSG = mat.pbrSpecularGlossiness.value;
 
             aimat->AddProperty(&mat.pbrSpecularGlossiness.isPresent, 1, AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS);
-            SetMaterialColorProperty(r, pbrSG.specularFactor, aimat, AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS_SPECULAR_FACTOR);
             SetMaterialColorProperty(r, pbrSG.diffuseFactor, aimat, AI_MATKEY_COLOR_DIFFUSE);
+            SetMaterialColorProperty(r, pbrSG.specularFactor, aimat, AI_MATKEY_COLOR_SPECULAR);
             aimat->AddProperty(&pbrSG.glossinessFactor, 1, AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS_GLOSSINESS_FACTOR);
-            SetMaterialTextureProperty(embeddedTexIdxs, r, pbrSG.specularGlossinessTexture, aimat, AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS_SPECULARGLOSSINESS_TEXTURE);
+
             SetMaterialTextureProperty(embeddedTexIdxs, r, pbrSG.diffuseTexture, aimat, aiTextureType_DIFFUSE);
+
+            SetMaterialTextureProperty(embeddedTexIdxs, r, pbrSG.specularGlossinessTexture, aimat, aiTextureType_SPECULAR);
         }
     }
 }