[gthumb] fixed keeping the center of the image after changing zoom

[Paolo Bacchilega <paobac src gnome org>]

commit f3771363c015282fb32a69dace759f8a4e716731
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Fri Oct 11 18:54:12 2013 +0200

    fixed keeping the center of the image after changing zoom

 gthumb/gth-image-viewer.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/gthumb/gth-image-viewer.c b/gthumb/gth-image-viewer.c
index a620e7f..040b830 100644
--- a/gthumb/gth-image-viewer.c
+++ b/gthumb/gth-image-viewer.c
@@ -350,6 +350,8 @@ set_zoom (GthImageViewer *self,
        /* try to keep the center of the view visible. */
        _gth_image_viewer_get_visible_area_size (self, &visible_width, &visible_height);
        zoom_ratio = zoom_level / self->priv->zoom_level;
+       center_x = center_x - self->image_area.x;
+       center_y = center_y - self->image_area.y;
        self->x_offset = ((self->x_offset + center_x) * zoom_ratio - visible_width / 2);
        self->y_offset = ((self->y_offset + center_y) * zoom_ratio - visible_height / 2);