From b10d5ffc8d22d18fe9ef940018a5aa54347b84b4 Mon Sep 17 00:00:00 2001
From: Daniel Drake <dsd@laptop.org>
Date: Sun, 11 Dec 2011 14:53:03 +0000
Subject: add some comments describing recent palette work

---
diff --git a/src/sugar3/graphics/palettewindow.py b/src/sugar3/graphics/palettewindow.py
index 71c035d..86c1611 100644
--- a/src/sugar3/graphics/palettewindow.py
+++ b/src/sugar3/graphics/palettewindow.py
@@ -119,7 +119,71 @@ class _PaletteMenuWidget(Gtk.Menu):
     def _position(self, widget, data):
         return self._popup_position[0], self._popup_position[1], False
 
+    def popup(self, invoker):
+        if self._up:
+            return
+
+        # We need to track certain mouse events in order to close the palette
+        # when the mouse leaves the palette and the invoker widget, but
+        # GtkMenu makes our lives hard here.
+        #
+        # GtkMenu takes a grab on the root window, meaning that normal
+        # enter/leave events are not sent to the relevant widgets.
+        # However, connecting enter-notify and leave-notify events in this
+        # GtkMenu subclass mean that we get to see the events being grabbed.
+        # With certain filtering in place (see _enter_notify_cb and
+        # _leave_notify_cb) we are able to accurately determine when the
+        # mouse leaves/enters the palette menu. Some spurious events are
+        # generated but the important thing is that the last event generated
+        # in response to a user action is always reliable (i.e. we will
+        # always get a leave event last if the user left the menu,
+        # even if we get some strange enter events leading up to it).
+        #
+        # This is complicated with submenus; in this case the submenu takes
+        # the grab, so we must also listen for events on any submenus of
+        # the palette and apply the same considerations.
+        #
+        # The remaining challenge is tracking when the mouse enters or leaves
+        # the invoker area. While the appropriate GtkMenu grab is active,
+        # we do get informed of such events, however these events will only
+        # arrive if the user has entered the menu. If the user hovers over
+        # the invoker and then leaves the invoker without entering the palette,
+        # we get no enter/leave event.
+        # We work around this by tracking mouse motion events. When the mouse
+        # moves, we compare the mouse coordinates to the region occupied by the
+        # invoker, and this lets us track enter/leave for the invoker widget.
+
+        self._invoker = invoker
+        self._find_all_menus(self)
+        for menu in self._menus:
+            if self._invoker:
+                menu.connect('motion-notify-event', self._motion_notify_cb)
+            menu.connect('enter-notify-event', self._enter_notify_cb)
+            menu.connect('leave-notify-event', self._leave_notify_cb)
+        self._entered = False
+        self._mouse_in_palette = False
+        self._mouse_in_invoker = False
+        Gtk.Menu.popup(self, None, None, self._position, None, 0, 0)
+        self._up = True
+
+    def popdown(self):
+        if not self._up:
+            return
+        Gtk.Menu.popdown(self)
+
+        for menu in self._menus:
+            menu.disconnect_by_func(self._motion_notify_cb)
+            menu.disconnect_by_func(self._enter_notify_cb)
+            menu.disconnect_by_func(self._leave_notify_cb)
+
+        self._up = False
+        self._menus = []
+        self._invoker = None
+
     def _find_all_menus(self, menu):
+        """
+        Recursively find all submenus of menu, adding them to self._menus.
+        """
         self._menus.append(menu)
         for child in menu.get_children():
             if not isinstance(child, Gtk.MenuItem):
@@ -160,44 +224,20 @@ class _PaletteMenuWidget(Gtk.Menu):
 
     def _reevaluate_state(self):
         if self._entered:
+            # If we previously advised that the mouse was inside, but now the
+            # mouse is outside both the invoker and the palette, notify that
+            # the mouse has left.
             if not self._mouse_in_palette and not self._mouse_in_invoker:
                 self._entered = False
                 self.emit('leave-notify')
         else:
+            # If we previously advised that the mouse had left, but now the
+            # mouse is inside either the palette or the invoker, notify that
+            # the mouse has entered.
             if self._mouse_in_palette or self._mouse_in_invoker:
                 self._entered = True
                 self.emit('enter-notify')
 
-    def popup(self, invoker):
-        if self._up:
-            return
-
-        self._invoker = invoker
-        self._find_all_menus(self)
-        for menu in self._menus:
-            if self._invoker:
-                menu.connect('motion-notify-event', self._motion_notify_cb)
-            menu.connect('enter-notify-event', self._enter_notify_cb)
-            menu.connect('leave-notify-event', self._leave_notify_cb)
-        self._entered = False
-        self._mouse_in_palette = False
-        self._mouse_in_invoker = False
-        Gtk.Menu.popup(self, None, None, self._position, None, 0, 0)
-        self._up = True
-
-    def popdown(self):
-        if not self._up:
-            return
-        Gtk.Menu.popdown(self)
-
-        for menu in self._menus:
-            menu.disconnect_by_func(self._motion_notify_cb)
-            menu.disconnect_by_func(self._enter_notify_cb)
-            menu.disconnect_by_func(self._leave_notify_cb)
-
-        self._up = False
-        self._menus = []
-        self._invoker = None
 
 class _PaletteWindowWidget(Gtk.Window):
 
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