[evince] libview: Allow zooming to the limits of the scale

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

commit 6d299b69e8ee9bd84b3bc51dc7a11af010119194
Author: David King <amigadave amigadave com>
Date:   Tue Oct 3 13:57:32 2017 -0300

    libview: Allow zooming to the limits of the scale
    
    If the current zoom level was within one zoom factor of the limit, it
    was not possible to scroll towards the limit. This made smooth scrolling
    near the limit awkward, as unless the scroll event had a large delta it
    was impossible to reach the zoom limit. Non-smooth scrolling was also
    affected, but it was just much more difficult to trigger.
    
    Fix this by allowing zooming while the current zoom level is within one
    zoom factor of the limit. Add a new ev_view_can_zoom() function to make
    zooming by a factor (as with smooth scrolling) more convenient.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=788480

 libview/ev-view.c |   22 ++++++++++++++++++----
 1 files changed, 18 insertions(+), 4 deletions(-)
---
diff --git a/libview/ev-view.c b/libview/ev-view.c
index ae49674..bb63b50 100644
--- a/libview/ev-view.c
+++ b/libview/ev-view.c
@@ -250,6 +250,8 @@ static double   zoom_for_size_automatic                      (GdkScreen *screen,
                                                              gdouble    doc_height,
                                                              int        target_width,
                                                              int        target_height);
+static gboolean ev_view_can_zoom                             (EvView *view,
+                                                              gdouble factor);
 static void     ev_view_zoom                                 (EvView *view,
                                                               gdouble factor);
 static void     ev_view_zoom_for_size                        (EvView *view,
@@ -4153,8 +4155,7 @@ ev_view_scroll_event (GtkWidget *widget, GdkEventScroll *event)
                        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)))
+                       if (ev_view_can_zoom (view, factor))
                                ev_view_zoom (view, factor);
                }
                        break;
@@ -8090,8 +8091,8 @@ update_can_zoom (EvView *view)
        min_scale = ev_document_model_get_min_scale (view->model);
        max_scale = ev_document_model_get_max_scale (view->model);
 
-       can_zoom_in = (view->scale * ZOOM_IN_FACTOR) <= max_scale;
-       can_zoom_out = (view->scale * ZOOM_OUT_FACTOR) > min_scale;
+       can_zoom_in = view->scale <= max_scale;
+       can_zoom_out = view->scale > min_scale;
 
        if (can_zoom_in != view->can_zoom_in) {
                view->can_zoom_in = can_zoom_in;
@@ -8291,6 +8292,19 @@ ev_view_reload (EvView *view)
 
 /*** Zoom and sizing mode ***/
 
+static gboolean
+ev_view_can_zoom (EvView *view, gdouble factor)
+{
+       if (factor == 1.0)
+               return TRUE;
+
+       else if (factor < 1.0) {
+               return ev_view_can_zoom_out (view);
+       } else {
+               return ev_view_can_zoom_in (view);
+       }
+}
+
 gboolean
 ev_view_can_zoom_in (EvView *view)
 {