[gnome-klotski] Add Unfullscreen button.

[Arnaud B. <arnaudb src gnome org>]

commit f138b92bc9c0a2150da3823e7746f987a134d77a
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Mon Feb 10 15:07:36 2020 +0100

    Add Unfullscreen button.

 data/klotski.css        |  4 ++++
 data/klotski.ui         | 32 ++++++++++++++++++++++++++++++--
 src/klotski-window.vala | 40 ++++++++++++++++++++++++++--------------
 3 files changed, 60 insertions(+), 16 deletions(-)
---
diff --git a/data/klotski.css b/data/klotski.css
index 7499d20..7c21881 100644
--- a/data/klotski.css
+++ b/data/klotski.css
@@ -15,6 +15,10 @@
    with GNOME Klotski.  If not, see <https://www.gnu.org/licenses/>.
 */
 
+button.unfullscreen-button {
+  margin:6px;
+}
+
 popover#puzzles-popover {
   padding: 10px;
 }
diff --git a/data/klotski.ui b/data/klotski.ui
index a450a15..0a7ce14 100644
--- a/data/klotski.ui
+++ b/data/klotski.ui
@@ -313,7 +313,6 @@
     <!-- <initial-focus name=""/> -->
     <property name="width-request">600</property>
     <property name="height-request">400</property>
-    <property name="border-width">25</property> <!-- TODO a view margin -->
     <signal name="size_allocate" handler="on_size_allocate"/>
     <signal name="window_state_event" handler="on_window_state_event"/>
     <signal name="destroy" handler="on_destroy"/>
@@ -376,7 +375,36 @@
       </object>
     </child>
     <child>
-      <placeholder/>
+      <object class="GtkOverlay" id="main_overlay">
+        <property name="visible">True</property>
+        <child>
+          <object class="GtkGrid" id="main_grid">
+            <property name="visible">True</property>
+            <property name="orientation">vertical</property>
+            <property name="margin">25</property> <!-- TODO use CSS -->
+          </object>
+        </child>
+        <child type="overlay">
+          <object class="GtkButton" id="unfullscreen_button">
+            <property name="visible">False</property>
+            <property name="halign">end</property>
+            <property name="valign">start</property>
+            <property name="action-name">win.unfullscreen</property>
+            <style>
+              <class name="image-button"/>
+              <class name="unfullscreen-button"/>
+              <class name="flat"/>
+            </style>
+            <child>
+              <object class="GtkImage">
+                <property name="icon-name">view-restore-symbolic</property>
+                <property name="visible">True</property>
+                <property name="icon-size">1</property>
+              </object>
+            </child>
+          </object>
+        </child>
+      </object>
     </child>
   </template>
 </interface>
diff --git a/src/klotski-window.vala b/src/klotski-window.vala
index 96ff447..6df0bc8 100644
--- a/src/klotski-window.vala
+++ b/src/klotski-window.vala
@@ -54,6 +54,9 @@ private class KlotskiWindow : ApplicationWindow
     [GtkChild] private TreeView treeview_challenge;
     [GtkChild] private TreeView treeview_skill;
 
+    [GtkChild] private Grid main_grid;
+    [GtkChild] private Button unfullscreen_button;
+
     /* Actions, to disable or enable */
     private SimpleAction prev_pack;
     private SimpleAction next_pack;
@@ -456,12 +459,13 @@ private class KlotskiWindow : ApplicationWindow
 
     private const GLib.ActionEntry win_actions [] =
     {
-        { "show-scores", show_scores     },
-        { "prev-pack",   prev_pack_cb    },
-        { "next-pack",   next_pack_cb    },
-        { "prev-puzzle", prev_puzzle_cb  },
-        { "next-puzzle", next_puzzle_cb  },
-        { "start-game",  start_puzzle_cb }
+        { "show-scores",    show_scores         },
+        { "prev-pack",      prev_pack_cb        },
+        { "next-pack",      next_pack_cb        },
+        { "prev-puzzle",    prev_puzzle_cb      },
+        { "next-puzzle",    next_puzzle_cb      },
+        { "start-game",     start_puzzle_cb     },
+        { "unfullscreen",   unfullscreen        }
     };
 
     private static string normalize_map_name (string name)
@@ -595,7 +599,9 @@ private class KlotskiWindow : ApplicationWindow
         view.halign = Align.FILL;
         view.can_focus = true;
         view.show ();
-        add (view);
+        view.hexpand = true;
+        view.vexpand = true;
+        main_grid.add (view);
 
         load_solved_state ();       // TODO use GSettings, or the history…
 
@@ -631,13 +637,13 @@ private class KlotskiWindow : ApplicationWindow
             window_is_maximized = (event.new_window_state & Gdk.WindowState.MAXIMIZED) != 0;
 
         /* fullscreen: saved as maximized */
- //     bool window_was_fullscreen = window_is_fullscreen;
+        bool window_was_fullscreen = window_is_fullscreen;
         if ((event.changed_mask & Gdk.WindowState.FULLSCREEN) != 0)
             window_is_fullscreen = (event.new_window_state & Gdk.WindowState.FULLSCREEN) != 0;
- //     if (window_was_fullscreen && !window_is_fullscreen)
- //         on_unfullscreen ();
- //     else if (!window_was_fullscreen && window_is_fullscreen)
- //         on_fullscreen ();
+        if (window_was_fullscreen && !window_is_fullscreen)
+            on_unfullscreen ();
+        else if (!window_was_fullscreen && window_is_fullscreen)
+            on_fullscreen ();
 
         /* tiled: not saved, but should not change saved window size */
         Gdk.WindowState tiled_state = Gdk.WindowState.TILED;
@@ -650,8 +656,14 @@ private class KlotskiWindow : ApplicationWindow
 
         return false;
     }
- // protected void on_fullscreen   () {}
- // protected void on_unfullscreen () {}
+    protected void on_fullscreen ()
+    {
+        unfullscreen_button.show ();
+    }
+    protected void on_unfullscreen ()
+    {
+        unfullscreen_button.hide ();
+    }
 
     [GtkCallback]
     private void on_destroy ()