[gthumb] fixed zoom not centered on the current position

[Paolo Bacchilega <paobac src gnome org>]

commit f84ac9ef9a2b8f5a5d9a992c0008c065484897fc
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Sat Jan 2 11:00:32 2016 +0100

    fixed zoom not centered on the current position

 gthumb/gth-image-viewer.c |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)
---
diff --git a/gthumb/gth-image-viewer.c b/gthumb/gth-image-viewer.c
index 7d10ac0..0ab0f67 100644
--- a/gthumb/gth-image-viewer.c
+++ b/gthumb/gth-image-viewer.c
@@ -347,18 +347,18 @@ set_zoom (GthImageViewer *self,
                image = gth_image_viewer_get_current_image (self);
                if (image != NULL) {
                        double quality_zoom;
-                       double zoom;
+                       double old_zoom_level;
                        int    x, y;
                        int    frame_border;
                        int    new_center_x, new_center_y;
 
                        quality_zoom = (double) self->priv->original_width / cairo_image_surface_get_width 
(image);
-                       zoom = self->priv->zoom_level * quality_zoom;
-                       x = (center_x + self->visible_area.x - self->image_area.x) / zoom;
-                       y = (center_y + self->visible_area.y - self->image_area.y) / zoom;
+                       old_zoom_level = self->priv->zoom_level * quality_zoom;
+                       x = (center_x + self->visible_area.x - self->image_area.x) / old_zoom_level;
+                       y = (center_y + self->visible_area.y - self->image_area.y) / old_zoom_level;
                        frame_border = _gth_image_viewer_get_frame_border (self);
-                       new_center_x = x * zoom_level * quality_zoom + frame_border;
-                       new_center_y = y * zoom_level * quality_zoom + frame_border;
+                       new_center_x = x * zoom_level * quality_zoom + frame_border + 1;
+                       new_center_y = y * zoom_level * quality_zoom + frame_border + 1;
 
                        self->visible_area.x = new_center_x - (self->visible_area.width / 2);
                        self->visible_area.y = new_center_y - (self->visible_area.height / 2);