[gtk/wip/carlosg/scroll-overshoot] gtk/scrolledwindow: Check for overshoot setting up kinetic scroll helpers

[Carlos Garnacho <carlosg src gnome org>]

commit 4ea8dd8f431d5f56b85f53f80190c8d4c6043663
Author: Carlos Garnacho <carlosg gnome org>
Date:   Fri Jul 29 20:34:55 2022 +0200

    gtk/scrolledwindow: Check for overshoot setting up kinetic scroll helpers
    
    We may have situations where velocity is 0/0, but are overshooting. Places where
    this happens are mouse wheels, and continuous scroll that ended up still before
    finish. In this situation we also want to run the animation for overshoot, so
    check for the corresponding axes to also set up the kinetic scroll helper.
    
    Closes: https://gitlab.gnome.org/GNOME/gtk/-/issues/5069

 gtk/gtkscrolledwindow.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index d2768d3ae0..ec2fcea1bf 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -3326,6 +3326,7 @@ gtk_scrolled_window_start_deceleration (GtkScrolledWindow *scrolled_window)
   GdkFrameClock *frame_clock;
   gint64 current_time;
   double elapsed;
+  int overshoot_x, overshoot_y;
 
   g_return_if_fail (priv->deceleration_id == 0);
 
@@ -3335,6 +3336,9 @@ gtk_scrolled_window_start_deceleration (GtkScrolledWindow *scrolled_window)
   elapsed = (current_time - priv->last_deceleration_time) / (double)G_TIME_SPAN_SECOND;
   priv->last_deceleration_time = current_time;
 
+  if (!_gtk_scrolled_window_get_overshoot (scrolled_window, &overshoot_x, &overshoot_y))
+    return;
+
   if (may_hscroll (scrolled_window))
     {
       double lower,upper;
@@ -3343,7 +3347,7 @@ gtk_scrolled_window_start_deceleration (GtkScrolledWindow *scrolled_window)
       gtk_scrolled_window_accumulate_velocity (&priv->hscrolling, elapsed, &priv->x_velocity);
       g_clear_pointer (&priv->hscrolling, gtk_kinetic_scrolling_free);
 
-      if (priv->x_velocity != 0)
+      if (priv->x_velocity != 0 || overshoot_x != 0)
         {
           hadjustment = gtk_scrollbar_get_adjustment (GTK_SCROLLBAR (priv->hscrollbar));
           lower = gtk_adjustment_get_lower (hadjustment);
@@ -3370,7 +3374,7 @@ gtk_scrolled_window_start_deceleration (GtkScrolledWindow *scrolled_window)
       gtk_scrolled_window_accumulate_velocity (&priv->vscrolling, elapsed, &priv->y_velocity);
       g_clear_pointer (&priv->vscrolling, gtk_kinetic_scrolling_free);
 
-      if (priv->y_velocity != 0)
+      if (priv->y_velocity != 0 || overshoot_y != 0)
         {
           vadjustment = gtk_scrollbar_get_adjustment (GTK_SCROLLBAR (priv->vscrollbar));
           lower = gtk_adjustment_get_lower(vadjustment);