GLTF: Use updated spec for material extension

This is now using the structure from
KhronosGroup/glTF#947 (comment),
though perhaps liable to change soon this is what's currently used by
Three.js.

code/glTFAssetWriter.inl

@@ -212,9 +212,12 @@ namespace glTF {
     namespace {
         inline void WriteColorOrTex(Value& obj, TexProperty& prop, const char* propName, MemoryPoolAllocator<>& al)
         {
-            if (prop.texture)
-                obj.AddMember(StringRef(propName), prop.texture->index, al);
-            else {
+            if (prop.texture) {
+                Value tex;
+                tex.SetObject();
+                tex.AddMember("index", prop.texture->index, al);
+                obj.AddMember(StringRef(propName), tex, al);
+            } else {
                 Value col;
                 obj.AddMember(StringRef(propName), MakeValue(col, prop.color, al), al);
             }
@@ -229,24 +232,20 @@ namespace glTF {
         Value v;
         v.SetObject();
         {
-            WriteColorOrTex(v, m.ambient, "ambient", w.mAl);
-            WriteColorOrTex(v, m.diffuse, "diffuse", w.mAl);
-            WriteColorOrTex(v, m.specular, "specular", w.mAl);
-            WriteColorOrTex(v, m.emission, "emission", w.mAl);
+            WriteColorOrTex(v, m.ambient, m.ambient.texture ? "ambientTexture" : "ambientFactor", w.mAl);
+            WriteColorOrTex(v, m.diffuse, m.diffuse.texture ? "diffuseTexture" : "diffuseFactor", w.mAl);
+            WriteColorOrTex(v, m.specular, m.specular.texture ? "specularTexture" : "specularFactor", w.mAl);
+            WriteColorOrTex(v, m.emission, m.emission.texture ? "emissionTexture" : "emissionFactor", w.mAl);
 
             if (m.transparent)
                 v.AddMember("transparency", m.transparency, w.mAl);
 
-            v.AddMember("shininess", m.shininess, w.mAl);
+            v.AddMember("shininessFactor", m.shininess, w.mAl);
         }
-
-        Value khr;
-        khr.SetObject();
-        khr.AddMember("technique", "PHONG", w.mAl);
-        khr.AddMember("values", v, w.mAl);
+        v.AddMember("type", "commonPhong", w.mAl);
         Value ext;
         ext.SetObject();
-        ext.AddMember("KHR_materials_common", khr, w.mAl);
+        ext.AddMember("KHR_materials_common", v, w.mAl);
         obj.AddMember("extensions", ext, w.mAl);
     }