[gtk/wip/carlosg/scrollbar-fixes: 1/2] gtkscrolledwindow: Look up correctly target in captured motion events

[Carlos Garnacho <carlosg src gnome org>]

commit 896ebdc9d75507dfbd56089aea1d7c959a7f7d44
Author: Carlos Garnacho <carlosg gnome org>
Date:   Thu Jul 9 16:10:55 2020 +0200

    gtkscrolledwindow: Look up correctly target in captured motion events
    
    Check correctly that the captured motion events are emitted towards the
    content or one of the scrollbars, in order to have it set the expected
    "over" state depending on whether the drag begins from the scrolledwindow
    content or one of the scrollbars.
    
    Fixes: https://gitlab.gnome.org/GNOME/gtk/-/issues/2879

 gtk/gtkscrolledwindow.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)
---
diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index 25312db293..bb74c4f17b 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -1169,10 +1169,13 @@ check_update_scrollbar_proximity (GtkScrolledWindow *sw,
   gboolean indicator_close, on_scrollbar, on_other_scrollbar;
 
   indicator_close = coords_close_to_indicator (sw, indicator, x, y);
-  on_scrollbar = (target == indicator->scrollbar);
+  on_scrollbar = (target == indicator->scrollbar ||
+                  gtk_widget_is_ancestor (target, indicator->scrollbar));
   on_other_scrollbar = (!on_scrollbar &&
                         (target == priv->hindicator.scrollbar ||
-                         target == priv->vindicator.scrollbar));
+                         target == priv->vindicator.scrollbar ||
+                         gtk_widget_is_ancestor (target, priv->hindicator.scrollbar) ||
+                         gtk_widget_is_ancestor (target, priv->vindicator.scrollbar)));
 
   if (indicator->over_timeout_id)
     {
@@ -1262,7 +1265,8 @@ captured_motion (GtkEventController *controller,
   if (priv->vscrollbar_visible)
     indicator_start_fade (&priv->vindicator, 1.0);
 
-  if (!target &&
+  if ((target == priv->child ||
+       gtk_widget_is_ancestor (target, priv->child)) &&
       (state & (GDK_BUTTON1_MASK | GDK_BUTTON2_MASK | GDK_BUTTON3_MASK)) != 0)
     {
       indicator_set_over (&priv->hindicator, FALSE);