app: add new action "view-scroll-center" with shortcut Shift+J

The zoom focus discussion on IRC suggests that everybody is annoyed
about centering behavior (or lack thereof), so here is a way to
explicitly center the image witout zooming.

NEWS

@@ -46,6 +46,8 @@ Usability:
   - Improve mouse wheel zooming behavior to keep the same point
     centered under the pointer even if the image is completely visible
     in the canvas.
+  - Add "View -> Center Image in Window" (Shift+J) as a quick way to
+    center the image at any zoom level.
 
 Translations:
 

app/actions/view-actions.c

@@ -97,6 +97,12 @@ static const GimpActionEntry view_actions[] =
     G_CALLBACK (view_close_cmd_callback),
     GIMP_HELP_FILE_CLOSE },
 
+  { "view-scroll-center", GIMP_ICON_CENTER,
+    NC_("view-action", "Center Image in Window"), "<shift>J",
+    NC_("view-action", "Scroll the image so that it is centered in the window"),
+    G_CALLBACK (view_scroll_center_cmd_callback),
+    GIMP_HELP_VIEW_SCROLL_CENTER },
+
   { "view-zoom-fit-in", GIMP_ICON_ZOOM_FIT_BEST,
     NC_("view-action", "_Fit Image in Window"), "<primary><shift>J",
     NC_("view-action", "Adjust the zoom ratio so that the image becomes fully visible"),
@@ -897,6 +903,8 @@ view_actions_update (GimpActionGroup *group,
   SET_SENSITIVE ("view-dot-for-dot", image);
   SET_ACTIVE    ("view-dot-for-dot", display && shell->dot_for_dot);
 
+  SET_SENSITIVE ("view-scroll-center", image);
+
   SET_SENSITIVE ("view-zoom-revert", revert_enabled);
   if (revert_enabled)
     {

app/actions/view-commands.c

@@ -125,6 +125,17 @@ view_close_cmd_callback (GtkAction *action,
     gimp_display_shell_close (shell, FALSE);
 }
 
+void
+view_scroll_center_cmd_callback (GtkAction *action,
+                                 gpointer   data)
+{
+  GimpDisplay *display;
+  return_if_no_display (display, data);
+
+  gimp_display_shell_scroll_center_image (gimp_display_get_shell (display),
+                                          TRUE, TRUE);
+}
+
 void
 view_zoom_fit_in_cmd_callback (GtkAction *action,
                                gpointer   data)

app/actions/view-commands.h

@@ -24,6 +24,9 @@ void   view_new_cmd_callback                    (GtkAction *action,
 void   view_close_cmd_callback                  (GtkAction *action,
                                                  gpointer   data);
 
+void   view_scroll_center_cmd_callback          (GtkAction *action,
+                                                 gpointer   data);
+
 void   view_zoom_fit_in_cmd_callback            (GtkAction *action,
                                                  gpointer   data);
 void   view_zoom_fill_cmd_callback              (GtkAction *action,

app/widgets/gimphelp-ids.h

@@ -85,6 +85,7 @@
 
 #define GIMP_HELP_VIEW_NEW                        "gimp-view-new"
 #define GIMP_HELP_VIEW_DOT_FOR_DOT                "gimp-view-dot-for-dot"
+#define GIMP_HELP_VIEW_SCROLL_CENTER              "gimp-view-scroll-center"
 #define GIMP_HELP_VIEW_ZOOM_REVERT                "gimp-view-zoom-revert"
 #define GIMP_HELP_VIEW_ZOOM_OUT                   "gimp-view-zoom-out"
 #define GIMP_HELP_VIEW_ZOOM_IN                    "gimp-view-zoom-in"

menus/image-menu.xml.in

@@ -294,6 +294,7 @@
         <separator />
         <menuitem action="view-rotate-other" />
       </menu>
+      <menuitem action="view-scroll-center" />
       <separator />
       <menuitem action="view-shrink-wrap" />
       <menuitem action="view-fullscreen" />