scrolledwindow: Cancel overshoot on dimension changes

If we scroll down in a list that's still being filled, we hit the edge and
initiate overshoot, and then the adjustment's upper value increases. This
leads to an unwanted bounce back.

Additionally, if in a similar situation the upper value decreases, the
overscroll glow gets stuck.

Update kinetic scrolling upper and lower value on changes, and immediately
cancel it if dimensions on that side change.

Fixes https://gitlab.gnome.org/GNOME/gtk/-/issues/3752

3 files changed, 79 insertions, 0 deletions

diff --git a/gtk/gtkkineticscrolling.c b/gtk/gtkkineticscrolling.c
index 9036e158dc..497627000b 100644
--- a/gtk/gtkkineticscrolling.c
+++ b/gtk/gtkkineticscrolling.c
@@ -124,6 +124,35 @@ gtk_kinetic_scrolling_new (gdouble lower,
   return data;
 }
 
+GtkKineticScrollingChange
+gtk_kinetic_scrolling_update_size (GtkKineticScrolling *data,
+                                   gdouble              lower,
+                                   gdouble              upper)
+{
+  GtkKineticScrollingChange change = GTK_KINETIC_SCROLLING_CHANGE_NONE;
+
+  if (lower != data->lower)
+    {
+      if (data->position <= lower)
+        change |= GTK_KINETIC_SCROLLING_CHANGE_LOWER;
+
+      data->lower = lower;
+    }
+
+  if (upper != data->upper)
+    {
+      if (data->position >= data->upper)
+        change |= GTK_KINETIC_SCROLLING_CHANGE_UPPER;
+
+      data->upper = upper;
+    }
+
+  if (data->phase == GTK_KINETIC_SCROLLING_PHASE_OVERSHOOTING)
+    change |= GTK_KINETIC_SCROLLING_CHANGE_IN_OVERSHOOT;
+
+  return change;
+}
+
 void
 gtk_kinetic_scrolling_free (GtkKineticScrolling *kinetic)
 {
diff --git a/gtk/gtkkineticscrolling.h b/gtk/gtkkineticscrolling.h
index d00f1d05f6..8155d57687 100644
--- a/gtk/gtkkineticscrolling.h
+++ b/gtk/gtkkineticscrolling.h
@@ -23,6 +23,13 @@
 
 G_BEGIN_DECLS
 
+typedef enum {
+  GTK_KINETIC_SCROLLING_CHANGE_NONE = 0,
+  GTK_KINETIC_SCROLLING_CHANGE_LOWER = 1 << 0,
+  GTK_KINETIC_SCROLLING_CHANGE_UPPER = 1 << 1,
+  GTK_KINETIC_SCROLLING_CHANGE_IN_OVERSHOOT = 1 << 2,
+} GtkKineticScrollingChange;
+
 typedef struct _GtkKineticScrolling GtkKineticScrolling;
 
 GtkKineticScrolling *    gtk_kinetic_scrolling_new  (gdouble               lower,
@@ -34,6 +41,10 @@ GtkKineticScrolling *    gtk_kinetic_scrolling_new  (gdouble               lower
                                                      gdouble               initial_velocity);
 void                     gtk_kinetic_scrolling_free (GtkKineticScrolling  *kinetic);
 
+GtkKineticScrollingChange gtk_kinetic_scrolling_update_size (GtkKineticScrolling *data,
+                                                             gdouble              lower,
+                                                             gdouble              upper);
+
 gboolean                 gtk_kinetic_scrolling_tick (GtkKineticScrolling  *data,
                                                      gdouble               time_delta,
                                                      gdouble              *position,
diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index bea7339f39..1909077220 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -3900,6 +3900,24 @@ gtk_scrolled_window_adjustment_changed (GtkAdjustment *adjustment,
 
 	  if (priv->hscrollbar_visible != visible)
 	    gtk_widget_queue_resize (GTK_WIDGET (scrolled_window));
+
+          if (priv->hscrolling)
+            {
+              GtkKineticScrollingChange change;
+              gdouble lower = gtk_adjustment_get_lower (adjustment);
+              gdouble upper = gtk_adjustment_get_upper (adjustment);
+              upper -= gtk_adjustment_get_page_size (adjustment);
+
+              change = gtk_kinetic_scrolling_update_size (priv->hscrolling, lower, upper);
+
+              if ((change & GTK_KINETIC_SCROLLING_CHANGE_IN_OVERSHOOT) &&
+                  (change & (GTK_KINETIC_SCROLLING_CHANGE_UPPER | GTK_KINETIC_SCROLLING_CHANGE_LOWER)))
+                {
+                  g_clear_pointer (&priv->hscrolling, gtk_kinetic_scrolling_free);
+                  priv->unclamped_hadj_value = gtk_adjustment_get_value (adjustment);
+                  gtk_scrolled_window_invalidate_overshoot (scrolled_window);
+                }
+            }
 	}
     }
   else if (adjustment == gtk_range_get_adjustment (GTK_RANGE (priv->vscrollbar)))
@@ -3914,8 +3932,29 @@ gtk_scrolled_window_adjustment_changed (GtkAdjustment *adjustment,
 
 	  if (priv->vscrollbar_visible != visible)
 	    gtk_widget_queue_resize (GTK_WIDGET (scrolled_window));
+
+          if (priv->vscrolling)
+            {
+              GtkKineticScrollingChange change;
+              gdouble lower = gtk_adjustment_get_lower (adjustment);
+              gdouble upper = gtk_adjustment_get_upper (adjustment);
+              upper -= gtk_adjustment_get_page_size (adjustment);
+
+              change = gtk_kinetic_scrolling_update_size (priv->vscrolling, lower, upper);
+
+              if ((change & GTK_KINETIC_SCROLLING_CHANGE_IN_OVERSHOOT) &&
+                  (change & (GTK_KINETIC_SCROLLING_CHANGE_UPPER | GTK_KINETIC_SCROLLING_CHANGE_LOWER)))
+                {
+                  g_clear_pointer (&priv->vscrolling, gtk_kinetic_scrolling_free);
+                  priv->unclamped_vadj_value = gtk_adjustment_get_value (adjustment);
+                  gtk_scrolled_window_invalidate_overshoot (scrolled_window);
+                }
+            }
 	}
     }
+
+  if (!priv->hscrolling && !priv->vscrolling)
+    gtk_scrolled_window_cancel_deceleration (scrolled_window);
 }
 
 static void