Unused Texture via user extension

addons/io_scene_gltf2/__init__.py

@@ -363,8 +363,11 @@ def __init__(self):
         default=False)
 
     export_unused_textures: BoolProperty(
-        name='Unused textures',
-        description='Export image texture nodes not assigned to any material',
+        name='Prepare Unused textures',
+        description=(
+            'Export image texture nodes not assigned to any material.'
+            'This feature is not standard, need an external extension to be included in the glTF file'
+        ),
         default=False)
 
     export_colors: BoolProperty(

addons/io_scene_gltf2/blender/exp/gltf2_blender_export.py

@@ -76,10 +76,15 @@ def __export(export_settings):
         additional_json_textures = fix_json([i.to_dict() for i in exporter.additional_data.additional_textures])
 
         # Now that we have the final json, we can add the additional data
-        if len(additional_json_textures) > 0:
-            if json.get('extras') is None:
-                json['extras'] = {}
-            json['extras']['additionalTextures'] = additional_json_textures
+        # We can not do that for all people, because we don't want this extra to become "a standard"
+        # So let's use the "extras" field filled by a user extension
+
+        export_user_extensions('gather_gltf_additional_textures_hook', export_settings, json, additional_json_textures)
+
+        # if len(additional_json_textures) > 0:
+        #     if json.get('extras') is None:
+        #         json['extras'] = {}
+        #     json['extras']['additionalTextures'] = additional_json_textures
 
     return json, buffer
 

example-addons/example_gltf_exporter_extension/readme.md

@@ -72,4 +72,5 @@ gather_animation_object_sampled_channel_target_hook(self, blender_object, channe
 gather_attribute_keep(self, keep_attribute, export_settings)
 gather_attribute_change(self, attribute, data, is_normalized_byte_color, export_settings)
 gather_attributes_change(self, attributes, export_settings)
+gather_gltf_additional_textures_hook(self, json, additioan_json_textures, export_settings)
 ```

tests/test/test.js

@@ -2150,7 +2150,8 @@ describe('Exporter', function() {
                 assert.strictEqual(asset.textures.length, 20);
             });
 
-            it('exports addtional textures & images', function() {
+            // These tests are disabled because they require an user extension to be registered
+            /*it('exports addtional textures & images', function() {
                 let gltfPath_1 = path.resolve(outDirPath, '33_unused_texture_and_image.gltf');
                 var asset = JSON.parse(fs.readFileSync(gltfPath_1));
 
@@ -2169,6 +2170,7 @@ describe('Exporter', function() {
                 assert.strictEqual(asset.materials.length, 1);
                 assert.strictEqual(asset.extras['additionalTextures'].length, 1);
             });
+            */
 
             it('exports addtional images', function() {
                 let gltfPath_1 = path.resolve(outDirPath, '33_unused_image.gltf');