Include the "zoom" functionality to increase or
 decrease the font size of the terminal, and return
 it to its original state.

 I continued the work by Rostislav Lisovy.

 I tried to improve the provided patch a little bit:
  * It uses the pango functions to specify the size of the font.
  * Use "<Ctrl>plus" and "<Ctrl>minus" as the default shourtcuts for
    the zoom.
  * Include the "Normal size" functionality in order to return
    to the size of the preferences.
  * Make the hot updating of the font preference and zoom cohexist.
  * Included consistent gtk icons.
  
 Still remaining issues:
  * With multiple tabs it sometimes works correctly, sometimes the
    whole window changes its size a little

Signed-off-by: Asier Llano <asierllano@gmail.com>

diff --git a/terminal/terminal-preferences.c b/terminal/terminal-preferences.c
index 0809118..b33f628 100644
--- a/terminal/terminal-preferences.c
+++ b/terminal/terminal-preferences.c
@@ -55,6 +55,9 @@ enum
   PROP_ACCEL_SHOW_TOOLBARS,
   PROP_ACCEL_SHOW_BORDERS,
   PROP_ACCEL_FULLSCREEN,
+  PROP_ACCEL_ZOOM_IN,
+  PROP_ACCEL_ZOOM_OUT,
+  PROP_ACCEL_ZOOM_NORMAL,
   PROP_ACCEL_SET_TITLE,
   PROP_ACCEL_RESET,
   PROP_ACCEL_RESET_AND_CLEAR,
@@ -444,6 +447,39 @@ terminal_preferences_class_init (TerminalPreferencesClass *klass)
                                                         EXO_PARAM_READWRITE));
 
   /**
+   * TerminalPreferences:accel-zoom-in:
+   **/
+  g_object_class_install_property (gobject_class,
+                                   PROP_ACCEL_ZOOM_IN,
+                                   g_param_spec_string ("accel-zoom-in",
+                                                        _("Zoom in"),
+                                                        "AccelZoomIn",
+                                                        "<Control>plus",
+                                                        EXO_PARAM_READWRITE));
+
+  /**
+   * TerminalPreferences:accel-zoom-out:
+   **/
+  g_object_class_install_property (gobject_class,
+                                   PROP_ACCEL_ZOOM_OUT,
+                                   g_param_spec_string ("accel-zoom-out",
+                                                        _("Zoom out"),
+                                                        "AccelZoomOut",
+                                                        "<Control>minus",
+                                                        EXO_PARAM_READWRITE));
+
+  /**
+   * TerminalPreferences:accel-zoom-normal:
+   **/
+  g_object_class_install_property (gobject_class,
+                                   PROP_ACCEL_ZOOM_NORMAL,
+                                   g_param_spec_string ("accel-zoom-normal",
+                                                        _("Normal size"),
+                                                        "AccelZoomNormal",
+                                                        "<Control>0",
+                                                        EXO_PARAM_READWRITE));
+
+  /**
    * TerminalPreferences:accel-set-title:
    **/
   g_object_class_install_property (gobject_class,
diff --git a/terminal/terminal-screen.c b/terminal/terminal-screen.c
index 1aaced5..36af2b9 100644
--- a/terminal/terminal-screen.c
+++ b/terminal/terminal-screen.c
@@ -153,6 +153,7 @@ struct _TerminalScreen
 
   guint                activity_timeout_id;
   time_t               last_size_change;
+  gint                 zoom;
 };
 
 
@@ -817,18 +818,36 @@ terminal_screen_update_font (TerminalScreen *screen)
 
   if (G_LIKELY (font_name != NULL))
     {
+      PangoFontDescription *font_desc = NULL;
+      font_desc = pango_font_description_from_string(font_name);
       vte_terminal_set_allow_bold (VTE_TERMINAL (screen->terminal), font_allow_bold);
 
+      if (screen->zoom)
+        {
+          gint font_size = pango_font_description_get_size (font_desc);
+          gint zoom = screen->zoom;
+          while (zoom > 0) {
+            font_size += font_size >> 3;
+            zoom--;
+          }
+          while (zoom < 0) {
+            font_size -= font_size >> 3;
+            zoom++;
+          }
+          pango_font_description_set_size (font_desc, font_size);
+        }
+
 #if TERMINAL_HAS_ANTI_ALIAS_SETTING
       antialias = font_anti_alias
                 ? VTE_ANTI_ALIAS_USE_DEFAULT
                 : VTE_ANTI_ALIAS_FORCE_DISABLE;
-      vte_terminal_set_font_from_string_full (VTE_TERMINAL (screen->terminal),
-                                              font_name, antialias);
+      vte_terminal_set_font_full (VTE_TERMINAL (screen->terminal),
+                                  font_desc, antialias);
 #else
-      vte_terminal_set_font_from_string (VTE_TERMINAL (screen->terminal), font_name);
+      vte_terminal_set_font (VTE_TERMINAL (screen->terminal), font_desc);
 #endif
 
+      pango_font_description_free (font_desc);
       g_free (font_name);
     }
 }
@@ -1883,3 +1902,29 @@ terminal_screen_focus (TerminalScreen *screen)
 
   gtk_widget_grab_focus (GTK_WIDGET (screen->terminal));
 }
+
+void
+terminal_screen_zoom (TerminalScreen *screen, gint change)
+{
+  /* Decide the new zoom */
+  if (change > 0)
+    {
+      if (screen->zoom >= 7)
+        return;
+      screen->zoom++;
+    }
+  else if (change < 0)
+    {
+      if (screen->zoom <= -7)
+        return;
+      screen->zoom --;
+    }
+  else {
+    if (!screen->zoom)
+      return;
+    screen->zoom = 0;
+  }
+
+  /* Update the font of the terminal with the new zoom */
+  terminal_screen_update_font(screen);
+}
diff --git a/terminal/terminal-screen.h b/terminal/terminal-screen.h
index 7498409..a322a72 100644
--- a/terminal/terminal-screen.h
+++ b/terminal/terminal-screen.h
@@ -88,6 +88,9 @@ GtkWidget   *terminal_screen_get_tab_label                (TerminalScreen *scree
 
 void         terminal_screen_focus                        (TerminalScreen *screen);
 
+void         terminal_screen_zoom                         (TerminalScreen *screen,
+                                                           gint change);
+
 G_END_DECLS
 
 #endif /* !__TERMINAL_SCREEN_H__ */
diff --git a/terminal/terminal-shortcut-editor.c b/terminal/terminal-shortcut-editor.c
index ed057f2..f45dc09 100644
--- a/terminal/terminal-shortcut-editor.c
+++ b/terminal/terminal-shortcut-editor.c
@@ -112,6 +112,9 @@ static const ToplevelMenu toplevel_menus[] =
       "accel-show-toolbars",
       "accel-show-borders",
       "accel-fullscreen",
+      "accel-zoom-in",
+      "accel-zoom-out",
+      "accel-zoom-normal",
       NULL,
     },
   },
diff --git a/terminal/terminal-window-ui.xml b/terminal/terminal-window-ui.xml
index 9709078..fb4c786 100644
--- a/terminal/terminal-window-ui.xml
+++ b/terminal/terminal-window-ui.xml
@@ -30,6 +30,10 @@
       <menuitem action="show-toolbars" />
       <menuitem action="show-borders" />
       <menuitem action="fullscreen" />
+      <separator />
+      <menuitem action="zoom-in" />
+      <menuitem action="zoom-out" />
+      <menuitem action="zoom-normal" />
     </menu>
     <menu action="terminal-menu">
       <menuitem action="set-title" />
diff --git a/terminal/terminal-window.c b/terminal/terminal-window.c
index 6294ef2..83fec68 100644
--- a/terminal/terminal-window.c
+++ b/terminal/terminal-window.c
@@ -166,6 +166,12 @@ static void            terminal_window_action_show_borders           (GtkToggleA
                                                                       TerminalWindow         *window);
 static void            terminal_window_action_fullscreen             (GtkToggleAction        *action,
                                                                       TerminalWindow         *window);
+static void            terminal_window_action_zoom_in                (GtkToggleAction        *action,
+                                                                      TerminalWindow         *window);
+static void            terminal_window_action_zoom_out               (GtkToggleAction        *action,
+                                                                      TerminalWindow         *window);
+static void            terminal_window_action_zoom_normal            (GtkToggleAction        *action,
+                                                                      TerminalWindow         *window);
 static void            terminal_window_action_prev_tab               (GtkAction              *action,
                                                                       TerminalWindow         *window);
 static void            terminal_window_action_next_tab               (GtkAction              *action,
@@ -231,6 +237,9 @@ static const GtkActionEntry action_entries[] =
     { "edit-toolbars", NULL, N_ ("_Toolbars..."), NULL, N_ ("Customize the toolbars"), G_CALLBACK (terminal_window_action_edit_toolbars), },
     { "preferences", GTK_STOCK_PREFERENCES, N_ ("Pr_eferences..."), NULL, N_ ("Open the Terminal preferences dialog"), G_CALLBACK (terminal_window_action_prefs), },
   { "view-menu", NULL, N_ ("_View"), NULL, NULL, NULL, },
+    { "zoom-in",  GTK_STOCK_ZOOM_IN,  N_ ("Zoom _in"), NULL, N_ ("Increase font size"), G_CALLBACK (terminal_window_action_zoom_in), },
+    { "zoom-out", GTK_STOCK_ZOOM_OUT, N_ ("Zoom _out"), NULL, N_ ("Reduce font size"), G_CALLBACK (terminal_window_action_zoom_out), },
+    { "zoom-normal", GTK_STOCK_ZOOM_100, N_("_Normal size"), NULL, N_ ("Use the original font size"), G_CALLBACK (terminal_window_action_zoom_normal), },
   { "terminal-menu", NULL, N_ ("_Terminal"), NULL, NULL, NULL, },
     { "set-title", NULL, N_ ("_Set Title..."), NULL, N_ ("Set a custom title for the current tab"), G_CALLBACK (terminal_window_action_set_title), },
     { "reset", GTK_STOCK_REFRESH, N_ ("_Reset"), NULL, N_ ("Reset"), G_CALLBACK (terminal_window_action_reset), },
@@ -1471,6 +1480,36 @@ terminal_window_action_fullscreen (GtkToggleAction *action,
 
 
 static void
+terminal_window_action_zoom_in (GtkToggleAction *action,
+                                TerminalWindow  *window)
+{
+  if (G_LIKELY (window->active != NULL) )
+    terminal_screen_zoom(window->active, 1);
+}
+
+
+
+static void
+terminal_window_action_zoom_out (GtkToggleAction *action,
+                                 TerminalWindow  *window)
+{
+  if (G_LIKELY (window->active != NULL) )
+    terminal_screen_zoom(window->active, -1);
+}
+
+
+
+static void
+terminal_window_action_zoom_normal (GtkToggleAction *action,
+                                    TerminalWindow  *window)
+{
+  if (G_LIKELY (window->active != NULL) )
+    terminal_screen_zoom(window->active, 0);
+}
+
+
+
+static void
 terminal_window_action_prev_tab (GtkAction       *action,
                                  TerminalWindow  *window)
 {