Fix calculation of smoothness and roughnessFactor conversion

Assets/VRM/UniGLTF/Scripts/IO/MaterialImporter.cs

@@ -164,9 +164,8 @@ public virtual Material CreateMaterial(int i, glTFMaterial x)
                     if (texture != null)
                     {
                         var prop = "_MetallicGlossMap";
-                        var smoothness = 1.0f - x.pbrMetallicRoughness.roughnessFactor;
-                        // Bake smoothness values into a texture.
-                        material.SetTexture(prop, texture.ConvertTexture(prop, smoothness));
+                        // Bake roughnessFactor values into a texture.
+                        material.SetTexture(prop, texture.ConvertTexture(prop, x.pbrMetallicRoughness.roughnessFactor));
                     }
 
                     material.SetFloat("_Metallic", 1.0f);

Assets/VRM/UniGLTF/Scripts/IO/TextureConverter.cs

@@ -51,11 +51,11 @@ class MetallicRoughnessConverter : ITextureConverter
     {
         private const string m_extension = ".metallicRoughness";
 
-        private float _smoothness;
+        private float _smoothnessOrRoughness;
 
-        public MetallicRoughnessConverter(float smoothness)
+        public MetallicRoughnessConverter(float smoothnessOrRoughness)
         {
-            _smoothness = smoothness;
+            _smoothnessOrRoughness = smoothnessOrRoughness;
         }
 
         public Texture2D GetImportTexture(Texture2D texture)
@@ -76,27 +76,36 @@ public Color32 Import(Color32 src)
         {
             // Roughness(glTF): dst.g -> Smoothness(Unity): src.a (with conversion)
             // Metallic(glTF) : dst.b -> Metallic(Unity)  : src.r
+
+            var pixelRoughnessFactor = src.g * _smoothnessOrRoughness; // roughness
+            var pixelSmoothness = 1.0f - Mathf.Sqrt(pixelRoughnessFactor);
+
             return new Color32
             {
                 r = src.b,
                 g = 0,
                 b = 0,
                 // Bake roughness values into a texture.
                 // See: https://github.com/dwango/UniVRM/issues/212.
-                a = (byte)(255 - Math.Min(src.g * (1.0f - _smoothness), 255)),
+                a = (byte)Mathf.Clamp(pixelSmoothness * 255, 0, 255),
             };
         }
 
         public Color32 Export(Color32 src)
         {
             // Smoothness(Unity): src.a -> Roughness(glTF): dst.g (with conversion)
             // Metallic(Unity)  : src.r -> Metallic(glTF) : dst.b
+
+            var pixelSmoothness = src.a * _smoothnessOrRoughness; // smoothness
+            // https://blogs.unity3d.com/jp/2016/01/25/ggx-in-unity-5-3/
+            var pixelRoughnessFactor = (1.0f - pixelSmoothness) * (1.0f - pixelSmoothness);
+
             return new Color32
             {
                 r = 0,
                 // Bake smoothness values into a texture.
                 // See: https://github.com/dwango/UniVRM/issues/212.
-                g = (byte)(255 - Math.Min(src.a * _smoothness, 255)),
+                g = (byte)Mathf.Clamp(pixelRoughnessFactor * 255, 0, 255),
                 b = src.r,
                 a = 255,
             };

Assets/VRM/UniGLTF/Scripts/IO/TextureItem.cs

@@ -36,7 +36,7 @@ public Texture2D Texture
         /// <param name="prop"></param>
         /// <param name="smoothness">used only when converting MetallicRoughness maps</param>
         /// <returns></returns>
-        public Texture2D ConvertTexture(string prop, float smoothness = 1.0f)
+        public Texture2D ConvertTexture(string prop, float smoothnessOrRoughness = 1.0f)
         {
             var convertedTexture = Converts.FirstOrDefault(x => x.Key == prop);
             if (convertedTexture.Value != null)
@@ -69,7 +69,7 @@ public Texture2D ConvertTexture(string prop, float smoothness = 1.0f)
 
             if (prop == "_MetallicGlossMap")
             {
-                var converted = new MetallicRoughnessConverter(smoothness).GetImportTexture(Texture);
+                var converted = new MetallicRoughnessConverter(smoothnessOrRoughness).GetImportTexture(Texture);
                 m_converts.Add(prop, converted);
                 return converted;
             }