[evince/wip/gpoo/gtk4-rebase-port: 64/96] ev-view: implement middle click drag

[Germán Poo-Caamaño <gpoo src gnome org>]

commit c821ed4febdba8dadda39e7906e44f9f4d458c79
Author: Qiu Wenbo <qiuwenbo kylinos com cn>
Date:   Wed Aug 18 17:27:03 2021 +0800

    ev-view: implement middle click drag
    
    Signed-off-by: Qiu Wenbo <qiuwenbo kylinos com cn>

 libview/ev-view.c | 301 ++++++++++++++++++++++++++++++------------------------
 1 file changed, 165 insertions(+), 136 deletions(-)
---
diff --git a/libview/ev-view.c b/libview/ev-view.c
index bec31a386..0e30b3205 100644
--- a/libview/ev-view.c
+++ b/libview/ev-view.c
@@ -5641,17 +5641,7 @@ ev_view_button_press_event (GtkGestureClick      *gesture,
                }
                        return;
                case GDK_BUTTON_MIDDLE:
-#if 0
-                       /* use root coordinates as reference point because
-                        * scrolling changes window relative coordinates */
-                       view->drag_info.start.x = event->x_root;
-                       view->drag_info.start.y = event->y_root;
-                       view->drag_info.hadj = gtk_adjustment_get_value (view->hadjustment);
-                       view->drag_info.vadj = gtk_adjustment_get_value (view->vadjustment);
-
-                       ev_view_set_cursor (view, EV_VIEW_CURSOR_DRAG);
                        ev_view_set_focused_element_at_location (view, x, y);
-#endif
                        return;
                case GDK_BUTTON_SECONDARY:
                        view->scroll_info.start_y = y;
@@ -5660,6 +5650,160 @@ ev_view_button_press_event (GtkGestureClick     *gesture,
        }
 }
 
+static gboolean
+ev_view_drag_update_momentum (EvView *view)
+{
+       int i;
+       if (!view->drag_info.in_drag)
+               return FALSE;
+
+       for (i = DRAG_HISTORY - 1; i > 0; i--) {
+               view->drag_info.buffer[i].x = view->drag_info.buffer[i-1].x;
+               view->drag_info.buffer[i].y = view->drag_info.buffer[i-1].y;
+       }
+
+       /* Momentum is a moving average of 10ms granularity over
+        * the last 100ms with each 10ms stored in buffer.
+        */
+
+       view->drag_info.momentum.x = (view->drag_info.buffer[DRAG_HISTORY - 1].x - 
view->drag_info.buffer[0].x);
+       view->drag_info.momentum.y = (view->drag_info.buffer[DRAG_HISTORY - 1].y - 
view->drag_info.buffer[0].y);
+
+       return TRUE;
+}
+
+static gboolean
+ev_view_scroll_drag_release (EvView *view)
+{
+       gdouble dhadj_value, dvadj_value;
+       gdouble oldhadjustment, oldvadjustment;
+       gdouble h_page_size, v_page_size;
+       gdouble h_upper, v_upper;
+       GtkAllocation allocation;
+
+       view->drag_info.momentum.x /= 1.2;
+       view->drag_info.momentum.y /= 1.2; /* Alter these constants to change "friction" */
+
+       gtk_widget_get_allocation (GTK_WIDGET (view), &allocation);
+
+       h_page_size = gtk_adjustment_get_page_size (view->hadjustment);
+       v_page_size = gtk_adjustment_get_page_size (view->vadjustment);
+
+       dhadj_value = h_page_size *
+                     (gdouble)view->drag_info.momentum.x / allocation.width;
+       dvadj_value = v_page_size *
+                     (gdouble)view->drag_info.momentum.y / allocation.height;
+
+       oldhadjustment = gtk_adjustment_get_value (view->hadjustment);
+       oldvadjustment = gtk_adjustment_get_value (view->vadjustment);
+
+       h_upper = gtk_adjustment_get_upper (view->hadjustment);
+       v_upper = gtk_adjustment_get_upper (view->vadjustment);
+
+       /* When we reach the edges, we need either to absorb some momentum and bounce by
+        * multiplying it on -0.5 or stop scrolling by setting momentum to 0. */
+       if (((oldhadjustment + dhadj_value) > (h_upper - h_page_size)) ||
+           ((oldhadjustment + dhadj_value) < 0))
+               view->drag_info.momentum.x = 0;
+       if (((oldvadjustment + dvadj_value) > (v_upper - v_page_size)) ||
+           ((oldvadjustment + dvadj_value) < 0))
+               view->drag_info.momentum.y = 0;
+
+       gtk_adjustment_set_value (view->hadjustment,
+                                 MIN (oldhadjustment + dhadj_value,
+                                      h_upper - h_page_size));
+       gtk_adjustment_set_value (view->vadjustment,
+                                 MIN (oldvadjustment + dvadj_value,
+                                      v_upper - v_page_size));
+
+       if (((view->drag_info.momentum.x < 1) && (view->drag_info.momentum.x > -1)) &&
+           ((view->drag_info.momentum.y < 1) && (view->drag_info.momentum.y > -1)))
+               return FALSE;
+       else
+               return TRUE;
+}
+
+static void
+on_middle_clicked_drag_begin (GtkGestureDrag   *self,
+                             gdouble            start_x,
+                             gdouble            start_y,
+                             EvView            *view)
+{
+       /* use root coordinates as reference point because
+        * scrolling changes window relative coordinates */
+       view->drag_info.hadj = gtk_adjustment_get_value (view->hadjustment);
+       view->drag_info.vadj = gtk_adjustment_get_value (view->vadjustment);
+
+       ev_view_set_cursor (view, EV_VIEW_CURSOR_DRAG);
+
+       view->drag_info.drag_timeout_id = g_timeout_add (10,
+                               (GSourceFunc)ev_view_drag_update_momentum, view);
+       /* Set 100 to choose how long it takes to build up momentum */
+       /* Clear out previous momentum info: */
+       for (int i = 0; i < DRAG_HISTORY; i++) {
+               view->drag_info.buffer[i].x = start_x;
+               view->drag_info.buffer[i].y = start_y;
+       }
+       view->drag_info.momentum.x = 0;
+       view->drag_info.momentum.y = 0;
+
+       view->drag_info.in_drag = TRUE;
+}
+
+static void
+on_middle_clicked_drag_end (GtkGestureDrag     *self,
+                           gdouble              offset_x,
+                           gdouble              offset_y,
+                           EvView              *view)
+{
+       view->drag_info.release_timeout_id =
+                       g_timeout_add (20, (GSourceFunc)ev_view_scroll_drag_release, view);
+
+       view->drag_info.in_drag = FALSE;
+}
+
+static void
+on_middle_clicked_drag_update (GtkGestureDrag  *self,
+                              gdouble           offset_x,
+                              gdouble           offset_y,
+                              EvView           *view)
+{
+       GdkEvent *event = gtk_event_controller_get_current_event (GTK_EVENT_CONTROLLER (self));
+       gdouble dhadj_value, dvadj_value;
+       GtkAllocation allocation;
+
+       gtk_widget_get_allocation (GTK_WIDGET (view), &allocation);
+
+       dhadj_value = gtk_adjustment_get_page_size (view->hadjustment) *
+                                     offset_x / allocation.width;
+       dvadj_value = gtk_adjustment_get_page_size (view->vadjustment) *
+                                     offset_y / allocation.height;
+
+       /* We will update the drag event's start position if
+        * the adjustment value is changed, but only if the
+        * change was not caused by this function. */
+
+       view->drag_info.in_notify = TRUE;
+
+       /* clamp scrolling to visible area */
+       gtk_adjustment_set_value (view->hadjustment, MIN (view->drag_info.hadj - dhadj_value,
+                                       gtk_adjustment_get_upper (view->hadjustment) -
+                                       gtk_adjustment_get_page_size (view->hadjustment)));
+       gtk_adjustment_set_value (view->vadjustment, MIN (view->drag_info.vadj - dvadj_value,
+                                       gtk_adjustment_get_upper (view->vadjustment) -
+                                       gtk_adjustment_get_page_size (view->vadjustment)));
+
+       view->drag_info.in_notify = FALSE;
+
+       gdouble x, y;
+
+       gdk_event_get_axis (event, GDK_AXIS_X, &x);
+       gdk_event_get_axis (event, GDK_AXIS_Y, &y);
+
+       view->drag_info.buffer[0].x = x;
+       view->drag_info.buffer[0].y = y;
+}
+
 #if 0
 static void
 ev_view_remove_all (EvView *view)
@@ -5803,80 +5947,6 @@ selection_scroll_timeout_cb (EvView *view)
        return TRUE;
 }
 
-static gboolean
-ev_view_drag_update_momentum (EvView *view)
-{
-       int i;
-       if (!view->drag_info.in_drag)
-               return FALSE;
-
-       for (i = DRAG_HISTORY - 1; i > 0; i--) {
-               view->drag_info.buffer[i].x = view->drag_info.buffer[i-1].x;
-               view->drag_info.buffer[i].y = view->drag_info.buffer[i-1].y;
-       }
-
-       /* Momentum is a moving average of 10ms granularity over
-        * the last 100ms with each 10ms stored in buffer.
-        */
-
-       view->drag_info.momentum.x = (view->drag_info.buffer[DRAG_HISTORY - 1].x - 
view->drag_info.buffer[0].x);
-       view->drag_info.momentum.y = (view->drag_info.buffer[DRAG_HISTORY - 1].y - 
view->drag_info.buffer[0].y);
-
-       return TRUE;
-}
-
-static gboolean
-ev_view_scroll_drag_release (EvView *view)
-{
-       gdouble dhadj_value, dvadj_value;
-       gdouble oldhadjustment, oldvadjustment;
-       gdouble h_page_size, v_page_size;
-       gdouble h_upper, v_upper;
-       GtkAllocation allocation;
-
-       view->drag_info.momentum.x /= 1.2;
-       view->drag_info.momentum.y /= 1.2; /* Alter these constants to change "friction" */
-
-       gtk_widget_get_allocation (GTK_WIDGET (view), &allocation);
-
-       h_page_size = gtk_adjustment_get_page_size (view->hadjustment);
-       v_page_size = gtk_adjustment_get_page_size (view->vadjustment);
-
-       dhadj_value = h_page_size *
-                     (gdouble)view->drag_info.momentum.x / allocation.width;
-       dvadj_value = v_page_size *
-                     (gdouble)view->drag_info.momentum.y / allocation.height;
-
-       oldhadjustment = gtk_adjustment_get_value (view->hadjustment);
-       oldvadjustment = gtk_adjustment_get_value (view->vadjustment);
-
-       h_upper = gtk_adjustment_get_upper (view->hadjustment);
-       v_upper = gtk_adjustment_get_upper (view->vadjustment);
-
-       /* When we reach the edges, we need either to absorb some momentum and bounce by
-        * multiplying it on -0.5 or stop scrolling by setting momentum to 0. */
-       if (((oldhadjustment + dhadj_value) > (h_upper - h_page_size)) ||
-           ((oldhadjustment + dhadj_value) < 0))
-               view->drag_info.momentum.x = 0;
-       if (((oldvadjustment + dvadj_value) > (v_upper - v_page_size)) ||
-           ((oldvadjustment + dvadj_value) < 0))
-               view->drag_info.momentum.y = 0;
-
-       gtk_adjustment_set_value (view->hadjustment,
-                                 MIN (oldhadjustment + dhadj_value,
-                                      h_upper - h_page_size));
-       gtk_adjustment_set_value (view->vadjustment,
-                                 MIN (oldvadjustment + dvadj_value,
-                                      v_upper - v_page_size));
-
-       if (((view->drag_info.momentum.x < 1) && (view->drag_info.momentum.x > -1)) &&
-           ((view->drag_info.momentum.y < 1) && (view->drag_info.momentum.y > -1)))
-               return FALSE;
-       else
-               return TRUE;
-}
-
-
 static void
 ev_view_motion_notify_event (GtkEventControllerMotion  *self,
                             gdouble                     x,
@@ -6111,52 +6181,6 @@ ev_view_motion_notify_event (GtkEventControllerMotion    *self,
                                                          event->x_root,
                                                          event->y_root);
                        view->drag_info.in_drag = start;
-                       view->drag_info.drag_timeout_id = g_timeout_add (10,
-                               (GSourceFunc)ev_view_drag_update_momentum, view);
-                       /* Set 100 to choose how long it takes to build up momentum */
-                       /* Clear out previous momentum info: */
-                       for (i = 0; i < DRAG_HISTORY; i++) {
-                               view->drag_info.buffer[i].x = event->x;
-                               view->drag_info.buffer[i].y = event->y;
-                       }
-                       view->drag_info.momentum.x = 0;
-                       view->drag_info.momentum.y = 0;
-               }
-
-               if (view->drag_info.in_drag) {
-                       int dx, dy;
-                       gdouble dhadj_value, dvadj_value;
-                       GtkAllocation allocation;
-
-                       view->drag_info.buffer[0].x = x;
-                       view->drag_info.buffer[0].y = y;
-
-                       dx = event->x_root - view->drag_info.start.x;
-                       dy = event->y_root - view->drag_info.start.y;
-
-                       gtk_widget_get_allocation (widget, &allocation);
-
-                       dhadj_value = gtk_adjustment_get_page_size (view->hadjustment) *
-                                     (gdouble)dx / allocation.width;
-                       dvadj_value = gtk_adjustment_get_page_size (view->vadjustment) *
-                                     (gdouble)dy / allocation.height;
-
-                       /* We will update the drag event's start position if
-                        * the adjustment value is changed, but only if the
-                        * change was not caused by this function. */
-                       view->drag_info.in_notify = TRUE;
-
-                       /* clamp scrolling to visible area */
-                       gtk_adjustment_set_value (view->hadjustment,
-                                                 MIN (view->drag_info.hadj - dhadj_value,
-                                                      gtk_adjustment_get_upper (view->hadjustment) -
-                                                      gtk_adjustment_get_page_size (view->hadjustment)));
-                       gtk_adjustment_set_value (view->vadjustment,
-                                                 MIN (view->drag_info.vadj - dvadj_value,
-                                                      gtk_adjustment_get_upper (view->vadjustment) -
-                                                      gtk_adjustment_get_page_size (view->vadjustment)));
-
-                       view->drag_info.in_notify = FALSE;
                }
 #endif
                break;
@@ -6307,12 +6331,6 @@ ev_view_button_release_event(GtkGestureClick             *self,
                return;
        }
 
-       if (view->drag_info.in_drag) {
-               view->drag_info.release_timeout_id =
-                       g_timeout_add (20,
-                                      (GSourceFunc)ev_view_scroll_drag_release, view);
-       }
-
        if (view->document && !view->drag_info.in_drag &&
            (view->pressed_button == GDK_BUTTON_PRIMARY ||
             view->pressed_button == GDK_BUTTON_MIDDLE)) {
@@ -8424,6 +8442,17 @@ ev_view_init (EvView *view)
                          G_CALLBACK (zoom_gesture_scale_changed_cb), view);
 
        gtk_widget_add_controller(widget, view->zoom_gesture);
+
+
+       controller = GTK_EVENT_CONTROLLER (gtk_gesture_drag_new ());
+       gtk_gesture_single_set_button (GTK_GESTURE_SINGLE (controller), GDK_BUTTON_MIDDLE);
+       g_signal_connect (controller, "drag-update",
+                         G_CALLBACK (on_middle_clicked_drag_update), view);
+       g_signal_connect (controller, "drag-begin",
+                         G_CALLBACK (on_middle_clicked_drag_begin), view);
+       g_signal_connect (controller, "drag-end",
+                         G_CALLBACK (on_middle_clicked_drag_end), view);
+       gtk_widget_add_controller (widget, controller);
 }
 
 /*** Callbacks ***/