[gtk/wip/carlosg/fix-accumulated-velocity: 3/5] gtkscrolledwindow: Change lifetime of kinetic scroll helpers

[Carlos Garnacho <carlosg src gnome org>]

commit adadcd3edb8ec1815ab548012ac48eae003acef0
Author: Carlos Garnacho <carlosg gnome org>
Date:   Tue Mar 15 22:01:36 2022 +0100

    gtkscrolledwindow: Change lifetime of kinetic scroll helpers
    
    In order to properly accumulate scroll velocities, we need to keep
    the kinetic scroll helpers after we have possibly stopped them
    in the process of initiating a further scroll flick.
    
    So, instead of stopping (and destroying) those helpers on scroll-begin,
    keep them until the next scroll-end if a scroll was initiated before
    kinetic scroll finished. This way we can fetch the last velocity when
    calculating the extra kick.
    
    In order to ensure the helpers don't live beyond what it is expected,
    we now also remove them after a finished hold event.
    
    Fixes the accumulation of scrolling velocity on consecutive scroll
    sequences.

 gtk/gtkscrolledwindow.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)
---
diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index 1bb8ebd971..423e0db1be 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -1056,6 +1056,11 @@ gtk_scrolled_window_decelerate (GtkScrolledWindow *scrolled_window,
         gtk_scrolled_window_start_deceleration (scrolled_window);
       priv->x_velocity = priv->y_velocity = 0;
     }
+  else
+    {
+      g_clear_pointer (&priv->hscrolling, gtk_kinetic_scrolling_free);
+      g_clear_pointer (&priv->vscrolling, gtk_kinetic_scrolling_free);
+    }
 }
 
 static void
@@ -3280,8 +3285,6 @@ scrolled_window_deceleration_cb (GtkWidget         *widget,
       gtk_adjustment_set_value (hadjustment, position);
       retval = G_SOURCE_CONTINUE;
     }
-  else if (priv->hscrolling)
-    g_clear_pointer (&priv->hscrolling, gtk_kinetic_scrolling_free);
 
   if (priv->vscrolling &&
       gtk_kinetic_scrolling_tick (priv->vscrolling, elapsed, &position, NULL))
@@ -3290,8 +3293,6 @@ scrolled_window_deceleration_cb (GtkWidget         *widget,
       gtk_adjustment_set_value (vadjustment, position);
       retval = G_SOURCE_CONTINUE;
     }
-  else if (priv->vscrolling)
-    g_clear_pointer (&priv->vscrolling, gtk_kinetic_scrolling_free);
 
   if (retval == G_SOURCE_REMOVE)
     gtk_scrolled_window_cancel_deceleration (scrolled_window);
@@ -3362,6 +3363,7 @@ gtk_scrolled_window_start_deceleration (GtkScrolledWindow *scrolled_window)
       GtkAdjustment *hadjustment;
 
       gtk_scrolled_window_accumulate_velocity (&priv->hscrolling, elapsed, &priv->x_velocity);
+      g_clear_pointer (&priv->hscrolling, gtk_kinetic_scrolling_free);
 
       hadjustment = gtk_scrollbar_get_adjustment (GTK_SCROLLBAR (priv->hscrollbar));
       lower = gtk_adjustment_get_lower (hadjustment);
@@ -3385,6 +3387,7 @@ gtk_scrolled_window_start_deceleration (GtkScrolledWindow *scrolled_window)
       GtkAdjustment *vadjustment;
 
       gtk_scrolled_window_accumulate_velocity (&priv->vscrolling, elapsed, &priv->y_velocity);
+      g_clear_pointer (&priv->vscrolling, gtk_kinetic_scrolling_free);
 
       vadjustment = gtk_scrollbar_get_adjustment (GTK_SCROLLBAR (priv->vscrollbar));
       lower = gtk_adjustment_get_lower(vadjustment);