[gtk/wip/exalm/overshoot-changes-gtk3] scrolledwindow: Cancel overshoot on dimension changes

[Alexander Mikhaylenko <alexm src gnome org>]

commit 27d38eca9a14fe32893ce5e97d2f0b542458f342
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Mon Mar 15 17:17:01 2021 +0500

    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

 gtk/gtkkineticscrolling.c | 29 +++++++++++++++++++++++++++++
 gtk/gtkkineticscrolling.h | 11 +++++++++++
 gtk/gtkscrolledwindow.c   | 39 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 79 insertions(+)
---
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