scripts/modules/bpy/utils/__init__.py

@@ -885,6 +885,12 @@ def register_tool(tool_cls, *, after=None, separator=False, group=False):
             "draw_settings": getattr(tool_cls, "draw_settings", None),
             "draw_cursor": getattr(tool_cls, "draw_cursor", None),
         })
+
+        if  hasattr( tool_cls, 'set_cb' ) and callable(tool_cls.set_cb ):
+            tool_def.handlers.set.append(tool_cls.set_cb)
+        if  hasattr( tool_cls, 'unset_cb' ) and callable(tool_cls.unset_cb ):
+            tool_def.handlers.set.append(tool_cls.unset_cb)
+
         tool_cls._bl_tool = tool_def
 
         keymap_data = tool_def.keymap
@@ -904,7 +910,7 @@ def register_tool(tool_cls, *, after=None, separator=False, group=False):
                 cls._km_action_simple(kc_default, kc, context_descr, tool_def.label, keymap_data)
         return tool_def
 
-    tool_converted = tool_from_class(tool_cls)
+    tool_created = tool_converted = tool_from_class(tool_cls)
 
     if group:
         # Create a new group
@@ -956,6 +962,7 @@ def register_tool(tool_cls, *, after=None, separator=False, group=False):
     if not changed:
         tools.extend(tool_def_insert)
 
+    return tool_created
 
 def unregister_tool(tool_cls):
     space_type = tool_cls.bl_space_type

scripts/startup/bl_ui/space_toolsystem_common.py

@@ -106,10 +106,16 @@ ToolDef = namedtuple(
         "draw_cursor",
         # Various options, see: `bpy.types.WorkSpaceTool.setup` options argument.
         "options",
+        # Handlers
+        "handlers"
     )
 )
 del namedtuple
 
+class ToolDefHandlers:
+    def __init__ (self):
+        self.set = []
+        self.unset = []
 
 def from_dict(kw_args):
     """
@@ -129,6 +135,7 @@ def from_dict(kw_args):
         "operator": None,
         "draw_settings": None,
         "draw_cursor": None,
+        "handlers" : ToolDefHandlers()
     }
     kw.update(kw_args)
 
@@ -326,11 +333,11 @@ class ToolSelectPanelHelper:
         return None, None, 0
 
     @classmethod
-    def _tool_get_by_id(cls, context, idname):
+    def _tool_get_by_id(cls, context, idname, mode = None):
         """
         Return the active Python tool definition and index (if in sub-group, else -1).
         """
-        for item, index in ToolSelectPanelHelper._tools_flatten_with_tool_index(cls.tools_from_context(context)):
+        for item, index in ToolSelectPanelHelper._tools_flatten_with_tool_index(cls.tools_from_context(context, mode)):
             if item is not None:
                 if item.idname == idname:
                     return (item, index)
@@ -985,6 +992,9 @@ def _activate_by_item(context, space_type, item, index, *, as_fallback=False):
     tool = ToolSelectPanelHelper._tool_active_from_context(context, space_type, create=True)
     tool_fallback_id = cls.tool_fallback_id
 
+    curr_tool = ToolSelectPanelHelper._tool_active_from_context(context, space_type)
+    curr_item, curr_index = cls._tool_get_by_id(context, getattr(curr_tool, "idname", None))
+
     if as_fallback:
         # To avoid complicating logic too much, isolate all fallback logic to this block.
         # This will set the tool again, using the item for the fallback instead of the primary tool.
@@ -1031,6 +1041,13 @@ def _activate_by_item(context, space_type, item, index, *, as_fallback=False):
     if keymap_fallback:
         keymap_fallback = keymap_fallback + " (fallback)"
 
+    if curr_item is not None:
+        for cb in curr_item.handlers.unset:
+            cb()
+
+    for cb in item.handlers.set:
+        cb()
+
     tool.setup(
         idname=item.idname,
         keymap=item.keymap[0] if item.keymap is not None else "",
@@ -1155,12 +1172,12 @@ def description_from_id(context, space_type, idname, *, use_operator=True):
     return ""
 
 
-def item_from_id(context, space_type, idname):
+def item_from_id(context, space_type, idname, mode = None):
     # Used directly for tooltips.
     cls = ToolSelectPanelHelper._tool_class_from_space_type(space_type)
     if cls is None:
         return None
-    item, _index = cls._tool_get_by_id(context, idname)
+    item, _index = cls._tool_get_by_id(context, idname, mode)
     return item