Implement KHR_materials_unlit with user extensions

addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_materials.py

@@ -135,13 +135,6 @@ def __gather_extensions(blender_material, export_settings):
     extension_wrapper = GLTF2ExtensionMaterials(blender_material)
     extensions = export_user_extensions(extension_wrapper, export_settings)
 
-    if bpy.app.version < (2, 80, 0):
-        if blender_material.use_shadeless:
-            extensions["KHR_materials_unlit"] = Extension("KHR_materials_unlit", {}, False)
-    else:
-        if gltf2_blender_get.get_socket_or_texture_slot(blender_material, "Background") is not None:
-            extensions["KHR_materials_unlit"] = Extension("KHR_materials_unlit", {}, False)
-
     # TODO specular glossiness extension
 
     return extensions if extensions else None

addons/io_scene_gltf2/io/exp/extensions/KHR_materials_unlit.py

@@ -0,0 +1,65 @@
+import bpy
+from io_scene_gltf2.io.com.gltf2_io_extensions import Extension
+from io_scene_gltf2.io.exp.gltf2_io_user_extensions import UserExtensionBase
+from io_scene_gltf2.blender.exp import gltf2_blender_get
+from io_scene_gltf2.io.exp.gltf2_io_user_extensions import GLTF2ExtensionMaterials
+
+class GLTF_PT_export_KHR_materials_unlit(bpy.types.Panel):
+    bl_space_type = 'FILE_BROWSER'
+    bl_region_type = 'TOOL_PROPS'
+    bl_label = "KHR_materials_unlit"
+    bl_parent_id = "GLTF_PT_export_user_extensions"
+    bl_options = {'DEFAULT_CLOSED'}
+
+    @classmethod
+    def poll(cls, context):
+        sfile = context.space_data
+        operator = sfile.active_operator
+        if operator.is_draco_available:
+            return operator.bl_idname == "EXPORT_SCENE_OT_gltf"
+
+    def draw_header(self, context):
+        sfile = context.space_data
+        operator = sfile.active_operator
+        self.layout.prop(operator, "export_KHR_materials_unlit_enabled", text="")
+
+    def draw(self, context):
+        layout = self.layout
+        layout.use_property_split = True
+        layout.use_property_decorate = False  # No animation.
+
+class KHR_materials_unlit(UserExtensionBase):
+    meta = {
+        'name': 'KHR_materials_unlit',
+        'isDraft': False,
+        'enable': True,
+        'url': (
+            'https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_unlit'
+        )
+    }
+
+    enabled = bpy.props.BoolProperty(
+        name='KHR_materials_unlit_enabled',
+        description='Enable/disable this extension',
+        default=True
+        )
+
+    def export(self, extension_wrapper, export_settings):
+
+        extension = None
+        if isinstance(extension_wrapper, GLTF2ExtensionMaterials):
+            blender_material = extension_wrapper.blender_material
+            if bpy.app.version < (2, 80, 0):
+                if blender_material.use_shadeless:
+                    extension = Extension("KHR_materials_unlit", {}, False)
+            else:
+                if gltf2_blender_get.get_socket_or_texture_slot(blender_material, "Background") is not None:
+                    extension = Extension("KHR_materials_unlit", {}, False)
+        return extension
+
+    def register_extension(self):
+        bpy.utils.register_class(GLTF_PT_export_KHR_materials_unlit)
+
+    def properties(self):
+        return {"enabled": self.enabled}
+