Pass transform events to children of containers.

This makes it possible of the children of containers to respond
to a button changing state differenty. Fixes #4578.

renpy/common/00compat.rpy

@@ -304,6 +304,7 @@ init -1100 python:
             config.drag_group_add_top = False
             config.transitions_use_child_placement = True
             config.interpolate_exprs = False
+            config.containers_pass_transform_events = False
 
     # The version of Ren'Py this script is intended for, or
     # None if it's intended for the current version.

renpy/config.py

@@ -1433,6 +1433,9 @@ defer_tl_scripts = False
 # Should transitions take placement from child displayables?
 transitions_use_child_placement = True
 
+# Should containiers pass transform events to their children?
+containers_pass_transform_events = True
+
 del os
 del collections
 

renpy/display/layout.py

@@ -131,6 +131,18 @@ class Container(renpy.display.displayable.Displayable):
 
         super(Container, self).__init__(**properties)
 
+    def set_transform_event(self, event):
+        """
+        Sets the transform event of this displayable to event.
+        """
+
+        super(Container, self).set_transform_event(event)
+
+        if renpy.config.containers_pass_transform_events:
+
+            for i in self.children:
+                i.set_transform_event(event)
+
     def _handles_event(self, event):
         for i in self.children:
             if i._handles_event(event):

sphinx/source/changelog.rst

@@ -370,6 +370,11 @@ projects from the command line.
 Other Changes
 -------------
 
+Containers (including fixed, hbox, vbox, side, grid, viewport, and vpgrid) now
+pass transform events (like hover and idle) to their children, meaning that
+children of a button can have their own transforms to respond to those
+events.
+
 :func:`persistent._clear` will re-run default statements that update
 persistent variables, making it possible to avoid persistent becoming
 entirely de-initialized.

sphinx/source/incompatible.rst

@@ -172,8 +172,17 @@ the old and new children provide the same placement information.
 
 To disable this, add to your game::
 
-    define config.transition_use_child_placement = false
+    define config.transition_use_child_placement = False
 
+**Containers pass Transform Events**
+Containers (including fixed, hbox, vbox, side, grid, viewport, and vpgrid) now
+pass transform events (like hover and idle) to their children, meaning that
+children of a button can have their own transforms to respond to those
+events.
+
+To disable this, add to your game::
+
+    define containers_pass_transform_events = True
 
 
 .. _incompatible-8.1.1: