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.

Backported from https://gitlab.gnome.org/GNOME/evince/-/commit/6d299b69

1 files changed, 19 insertions, 6 deletions

diff --git a/libview/ev-view.c b/libview/ev-view.c
index 68ca0970..5301079d 100644
--- a/libview/ev-view.c
+++ b/libview/ev-view.c
@@ -229,6 +229,8 @@ 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_for_size                        (EvView *view,
 							      int     width,
 							      int     height);
@@ -3819,8 +3821,7 @@ 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;
@@ -6472,8 +6473,7 @@ zoom_gesture_scale_changed_cb (GtkGestureZoom *gesture,
 
 	gtk_gesture_get_bounding_box_center (GTK_GESTURE (gesture), &view->zoom_center_x, &view->zoom_center_y);
 
-	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);
 }
 
@@ -6906,8 +6906,8 @@ 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;
@@ -7099,6 +7099,19 @@ 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)
 {