From: Adrien Plazas <kekun.plazas@laposte.net>
Date: Sat, 6 Jul 2019 11:05:24 +0200
Subject: scrolledwindow: Set deceleration value based on the device

This makes it nicer on phones by avoiding having to scroll too much on a
touch screen and it makes it match the changes we applied to WebKitGTK
for the same reasons.
---
 gtk/gtkscrolledwindow.c | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index a931d2b..e173e57 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -177,6 +177,7 @@
 /* Kinetic scrolling */
 #define MAX_OVERSHOOT_DISTANCE 100
 #define DECELERATION_FRICTION 4
+#define DECELERATION_FRICTION_TOUCH 1
 #define OVERSHOOT_FRICTION 20
 #define SCROLL_CAPTURE_THRESHOLD_MS 150
 #define VELOCITY_ACCUMULATION_FLOOR 0.33
@@ -396,7 +397,8 @@ static gboolean _gtk_scrolled_window_get_overshoot (GtkScrolledWindow *scrolled_
                                                     gint              *overshoot_x,
                                                     gint              *overshoot_y);
 
-static void     gtk_scrolled_window_start_deceleration (GtkScrolledWindow *scrolled_window);
+static void     gtk_scrolled_window_start_deceleration (GtkScrolledWindow *scrolled_window,
+                                                        gboolean           is_dragging);
 static gint     _gtk_scrolled_window_get_scrollbar_spacing (GtkScrolledWindow *scrolled_window);
 
 static void     gtk_scrolled_window_update_use_indicators (GtkScrolledWindow *scrolled_window);
@@ -1051,7 +1053,8 @@ scrolled_window_drag_end_cb (GtkScrolledWindow *scrolled_window,
 static void
 gtk_scrolled_window_decelerate (GtkScrolledWindow *scrolled_window,
                                 gdouble            x_velocity,
-                                gdouble            y_velocity)
+                                gdouble            y_velocity,
+                                gboolean           is_dragging)
 {
   GtkScrolledWindowPrivate *priv = scrolled_window->priv;
   gboolean overshoot;
@@ -1068,7 +1071,7 @@ gtk_scrolled_window_decelerate (GtkScrolledWindow *scrolled_window,
 
   if (priv->x_velocity != 0 || priv->y_velocity != 0 || overshoot)
     {
-      gtk_scrolled_window_start_deceleration (scrolled_window);
+      gtk_scrolled_window_start_deceleration (scrolled_window, is_dragging);
       priv->x_velocity = priv->y_velocity = 0;
     }
 }
@@ -1078,7 +1081,7 @@ scrolled_window_swipe_cb (GtkScrolledWindow *scrolled_window,
                           gdouble            x_velocity,
                           gdouble            y_velocity)
 {
-  gtk_scrolled_window_decelerate (scrolled_window, -x_velocity, -y_velocity);
+  gtk_scrolled_window_decelerate (scrolled_window, -x_velocity, -y_velocity, TRUE);
 }
 
 static void
@@ -3490,7 +3493,7 @@ start_scroll_deceleration_cb (gpointer user_data)
   if (!priv->deceleration_id)
     {
       uninstall_scroll_cursor (scrolled_window);
-      gtk_scrolled_window_start_deceleration (scrolled_window);
+      gtk_scrolled_window_start_deceleration (scrolled_window, FALSE);
     }
 
   return FALSE;
@@ -3638,7 +3641,7 @@ gtk_scrolled_window_scroll_event (GtkWidget      *widget,
 
       if (start_deceleration &&
           scroll_history_finish (scrolled_window, &vel_x, &vel_y))
-        gtk_scrolled_window_decelerate (scrolled_window, vel_x, vel_y);
+        gtk_scrolled_window_decelerate (scrolled_window, vel_x, vel_y, FALSE);
       else if (_gtk_scrolled_window_get_overshoot (scrolled_window, NULL, NULL))
         {
           priv->scroll_events_overshoot_id =
@@ -3790,12 +3793,14 @@ gtk_scrolled_window_accumulate_velocity (GtkKineticScrolling **scrolling, double
 }
 
 static void
-gtk_scrolled_window_start_deceleration (GtkScrolledWindow *scrolled_window)
+gtk_scrolled_window_start_deceleration (GtkScrolledWindow *scrolled_window,
+                                        gboolean           is_deceleration)
 {
   GtkScrolledWindowPrivate *priv = scrolled_window->priv;
   GdkFrameClock *frame_clock;
   gint64 current_time;
   double elapsed;
+  gdouble friction = is_deceleration ? DECELERATION_FRICTION_TOUCH : DECELERATION_FRICTION;
 
   g_return_if_fail (priv->deceleration_id == 0);
 
@@ -3820,7 +3825,7 @@ gtk_scrolled_window_start_deceleration (GtkScrolledWindow *scrolled_window)
         gtk_kinetic_scrolling_new (lower,
                                    upper,
                                    MAX_OVERSHOOT_DISTANCE,
-                                   DECELERATION_FRICTION,
+                                   friction,
                                    OVERSHOOT_FRICTION,
                                    priv->unclamped_hadj_value,
                                    priv->x_velocity);
@@ -3843,7 +3848,7 @@ gtk_scrolled_window_start_deceleration (GtkScrolledWindow *scrolled_window)
         gtk_kinetic_scrolling_new (lower,
                                    upper,
                                    MAX_OVERSHOOT_DISTANCE,
-                                   DECELERATION_FRICTION,
+                                   friction,
                                    OVERSHOOT_FRICTION,
                                    priv->unclamped_vadj_value,
                                    priv->y_velocity);
@@ -4666,7 +4671,7 @@ gtk_scrolled_window_grab_notify (GtkWidget *widget,
                                      priv->drag_device))
     {
       if (_gtk_scrolled_window_get_overshoot (scrolled_window, NULL, NULL))
-        gtk_scrolled_window_start_deceleration (scrolled_window);
+        gtk_scrolled_window_start_deceleration (scrolled_window, FALSE);
       else
         gtk_scrolled_window_cancel_deceleration (scrolled_window);
     }