[evince] libview: Enable GDK_SMOOTH_SCROLL events for view

[Carlos Garcia Campos <carlosgc src gnome org>]

commit 34d0d5df84f22ffba652acc3a4e582d204920b88
Author: Xiao-Long Chen <chenxiaolong cxl epac to>
Date:   Thu Oct 11 14:55:48 2012 -0400

    libview: Enable GDK_SMOOTH_SCROLL events for view
    
    This enables the smooth/kinetic scrolling support found in GTK+ 3.3.18
    with the document view, and handles them for the Ctrl+scroll,
    Shift+scroll, and non-continuous best-fit mode scrolling cases.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=674098

 libview/ev-view-private.h |    2 +
 libview/ev-view.c         |   71 +++++++++++++++++++++++++++++++-------------
 2 files changed, 52 insertions(+), 21 deletions(-)
---
diff --git a/libview/ev-view-private.h b/libview/ev-view-private.h
index f075dec..3d1de5c 100644
--- a/libview/ev-view-private.h
+++ b/libview/ev-view-private.h
@@ -145,6 +145,8 @@ struct _EvView {
        gint scroll_x;
        gint scroll_y;  
 
+       /* Delta sum for emulating normal scrolling */
+       gdouble       total_delta;
        PendingScroll pending_scroll;
        gboolean      pending_resize;
        EvPoint       pending_point;
diff --git a/libview/ev-view.c b/libview/ev-view.c
index e656db5..3a6bde3 100644
--- a/libview/ev-view.c
+++ b/libview/ev-view.c
@@ -3392,22 +3392,30 @@ ev_view_scroll_event (GtkWidget *widget, GdkEventScroll *event)
        EvView *view = EV_VIEW (widget);
        guint state;
 
-        if (event->direction == GDK_SCROLL_SMOOTH)
-                return FALSE;
-
        state = event->state & gtk_accelerator_get_default_mod_mask ();
 
        if (state == GDK_CONTROL_MASK) {
                ev_document_model_set_sizing_mode (view->model, EV_SIZING_FREE);
-               if (event->direction == GDK_SCROLL_UP ||
-                   event->direction == GDK_SCROLL_LEFT) {
-                       if (ev_view_can_zoom_in (view)) {
-                               ev_view_zoom_in (view);
-                       }
-               } else {
-                       if (ev_view_can_zoom_out (view)) {
+               switch (event->direction) {
+               case GDK_SCROLL_DOWN:
+               case GDK_SCROLL_RIGHT:
+                       if (ev_view_can_zoom_out (view))
                                ev_view_zoom_out (view);
-                       }
+                       break;
+               case GDK_SCROLL_UP:
+               case GDK_SCROLL_LEFT:
+                       if (ev_view_can_zoom_in (view))
+                               ev_view_zoom_in (view);
+                       break;
+               case GDK_SCROLL_SMOOTH: {
+                       gdouble delta = event->delta_x + event->delta_y;
+                       gdouble factor = pow (delta < 0 ? ZOOM_IN_FACTOR : ZOOM_OUT_FACTOR, fabs (delta));
+
+                       if ((factor < 1.0 && ev_view_can_zoom_out (view)) ||
+                           (factor >= 1.0 && ev_view_can_zoom_in (view)))
+                               ev_view_zoom (view, factor);
+               }
+                       break;
                }
 
                return TRUE;
@@ -3425,6 +3433,13 @@ ev_view_scroll_event (GtkWidget *widget, GdkEventScroll *event)
                        event->direction = GDK_SCROLL_RIGHT;
                else if (event->direction == GDK_SCROLL_RIGHT)
                        event->direction = GDK_SCROLL_DOWN;
+               else if (event->direction == GDK_SCROLL_SMOOTH) {
+                       /* Swap the deltas for perpendicular direction */
+                       gdouble tmp_delta = event->delta_x;
+
+                       event->delta_x = event->delta_y;
+                       event->delta_y = tmp_delta;
+               }
 
                event->state &= ~GDK_SHIFT_MASK;
                state &= ~GDK_SHIFT_MASK;
@@ -3432,16 +3447,29 @@ ev_view_scroll_event (GtkWidget *widget, GdkEventScroll *event)
 
        if (state == 0 && view->sizing_mode == EV_SIZING_FIT_PAGE && !view->continuous) {
                switch (event->direction) {
-                       case GDK_SCROLL_DOWN:
-                       case GDK_SCROLL_RIGHT:
-                               ev_view_next_page (view);       
-                               break;
-                       case GDK_SCROLL_UP:
-                       case GDK_SCROLL_LEFT:
-                               ev_view_previous_page (view);
-                               break;
-                        case GDK_SCROLL_SMOOTH:
-                                g_assert_not_reached ();
+               case GDK_SCROLL_DOWN:
+               case GDK_SCROLL_RIGHT:
+                       ev_view_next_page (view);
+                       break;
+               case GDK_SCROLL_UP:
+               case GDK_SCROLL_LEFT:
+                       ev_view_previous_page (view);
+                       break;
+               case GDK_SCROLL_SMOOTH: {
+                       gdouble decrement;
+
+                       /* Emulate normal scrolling by summing the deltas */
+                       view->total_delta += event->delta_x + event->delta_y;
+
+                       decrement = view->total_delta < 0 ? -1.0 : 1.0;
+                       for (; fabs (view->total_delta) >= 1.0; view->total_delta -= decrement) {
+                               if (decrement < 0)
+                                       ev_view_previous_page (view);
+                               else
+                                       ev_view_next_page (view);
+                       }
+               }
+                       break;
                }
 
                return TRUE;
@@ -5014,6 +5042,7 @@ ev_view_init (EvView *view)
                               GDK_BUTTON_PRESS_MASK |
                               GDK_BUTTON_RELEASE_MASK |
                               GDK_SCROLL_MASK |
+                              GDK_SMOOTH_SCROLL_MASK |
                               GDK_KEY_PRESS_MASK |
                               GDK_POINTER_MOTION_MASK |
                               GDK_POINTER_MOTION_HINT_MASK |