Option to export VC even if not used in node tree

addons/io_scene_gltf2/__init__.py

@@ -488,9 +488,33 @@ class ExportGLTF2_Base(ConvertGLTF2_Base):
         ),
         default=False)
 
-    export_colors: BoolProperty(
-        name='Dummy',
-        description='Keep for compatibility only',
+
+    export_vertex_color: EnumProperty(
+        name='Use Vertex Color',
+        items=(
+            ('MATERIAL', 'Material',
+            'Export vertex color when used by material'),
+            ('ACTIVE', 'Active',
+            'Export active vertex color'),
+            ('NONE', 'None',
+            'Do not export vertex color')),
+        description='How to export vertex color',
+        default='MATERIAL'
+    )
+
+    export_all_vertex_colors: BoolProperty(
+        name='Export all vertex colors',
+        description=(
+            'Export all vertex colors, even if not used by any material. '
+            'If no Vertex Color is used in the mesh materials, a fake COLOR_0 will be created, '
+            'in order to keep material unchanged'
+        ),
+        default=True
+    )
+
+    export_active_vertex_color_when_no_material: BoolProperty(
+        name='Export active vertex color when no material',
+        description='When there is no material on object, export active vertex color.',
         default=True
     )
 
@@ -1058,6 +1082,14 @@ def execute(self, context):
         export_settings['gltf_attributes'] = self.export_attributes
         export_settings['gltf_cameras'] = self.export_cameras
 
+        export_settings['gltf_vertex_color'] = self.export_vertex_color
+        if self.export_vertex_color == 'NONE':
+            export_settings['gltf_all_vertex_colors'] = False
+            export_settings['gltf_active_vertex_color_when_no_material'] = False
+        else:
+            export_settings['gltf_all_vertex_colors'] = self.export_all_vertex_colors
+            export_settings['gltf_active_vertex_color_when_no_material'] = self.export_active_vertex_color_when_no_material
+
         export_settings['gltf_unused_textures'] = self.export_unused_textures
         export_settings['gltf_unused_images'] = self.export_unused_images
 
@@ -1350,6 +1382,23 @@ def export_panel_data_mesh(layout, operator):
             col = body.column()
             col.prop(operator, 'export_shared_accessors')
 
+            header, sub_body = body.panel("GLTF_export_data_material_vertex_color", default_closed=True)
+            header.label(text="Vertex Colors")
+            if sub_body:
+                row = sub_body.row()
+                row.prop(operator, 'export_vertex_color')
+                if operator.export_vertex_color == "ACTIVE":
+                    row = sub_body.row()
+                    row.label(text="Note that fully compliant glTF 2.0 engine/viewer will use it as multiplicative factor for base color.", icon='ERROR')
+                    row = sub_body.row()
+                    row.label(text="If you want to use VC for any other purpose than vertex color, you should use custom attributes.")
+                row = sub_body.row()
+                row.active = operator.export_vertex_color != "NONE"
+                row.prop(operator, 'export_all_vertex_colors')
+                row = sub_body.row()
+                row.active = operator.export_vertex_color != "NONE"
+                row.prop(operator, 'export_active_vertex_color_when_no_material')
+
 
 def export_panel_data_material(layout, operator):
     header, body = layout.panel("GLTF_export_data_material", default_closed=True)

addons/io_scene_gltf2/blender/com/gltf2_blender_conversion.py

@@ -101,7 +101,8 @@ def get_component_type(attribute_component_type):
         "FLOAT_VECTOR_4": gltf2_io_constants.ComponentType.Float,
         "INT": gltf2_io_constants.ComponentType.Float, # No signed Int in glTF accessor
         "FLOAT": gltf2_io_constants.ComponentType.Float,
-        "BOOLEAN": gltf2_io_constants.ComponentType.Float
+        "BOOLEAN": gltf2_io_constants.ComponentType.Float,
+        "UNSIGNED_BYTE": gltf2_io_constants.ComponentType.UnsignedByte
     }.get(attribute_component_type)
 
 def get_channel_from_target(target):
@@ -147,7 +148,8 @@ def get_numpy_type(attribute_component_type):
         "FLOAT_VECTOR_4": np.float32,
         "INT": np.float32, #signed integer are not supported by glTF
         "FLOAT": np.float32,
-        "BOOLEAN": np.float32
+        "BOOLEAN": np.float32,
+        "UNSIGNED_BYTE": np.uint8,
     }.get(attribute_component_type)
 
 def get_attribute_type(component_type, data_type):

addons/io_scene_gltf2/blender/exp/gltf2_blender_gather_primitive_attributes.py

@@ -203,6 +203,28 @@ def __gather_attribute(blender_primitive, attribute, export_settings):
             )
         }
 
+    elif attribute.startswith("COLOR_") and blender_primitive["attributes"][attribute]['component_type'] == gltf2_io_constants.ComponentType.UnsignedByte:
+        # We are in special case where we fake a COLOR_0 attribute with UNSIGNED_BYTE
+        # We need to normalize it
+
+        export_user_extensions('gather_attribute_change', export_settings, attribute, data, True)
+
+        return { attribute : gltf2_io.Accessor(
+                buffer_view=gltf2_io_binary_data.BinaryData(data['data'].tobytes(), gltf2_io_constants.BufferViewTarget.ARRAY_BUFFER),
+                byte_offset=None,
+                component_type=data['component_type'],
+                count=len(data['data']),
+                extensions=None,
+                extras=None,
+                max=None,
+                min=None,
+                name=None,
+                normalized=True,
+                sparse=None,
+                type=data['data_type'],
+            )
+        }
+
     elif attribute.startswith("JOINTS_") or attribute.startswith("WEIGHTS_"):
         return __gather_skins(blender_primitive, export_settings)