canvas::Layout: add clear method to remove all items.

simgear/canvas/layout/BoxLayout.cxx

@@ -121,6 +121,13 @@ namespace canvas
     return item;
   }
 
+  //----------------------------------------------------------------------------
+  void BoxLayout::clear()
+  {
+    _layout_items.clear();
+    invalidate();
+  }
+
   //----------------------------------------------------------------------------
   void BoxLayout::setStretch(size_t index, int stretch)
   {

simgear/canvas/layout/BoxLayout.hxx

@@ -58,6 +58,7 @@ namespace canvas
       virtual size_t count() const;
       virtual LayoutItemRef itemAt(size_t index);
       virtual LayoutItemRef takeAt(size_t index);
+      virtual void clear();
 
       /**
        * Set the stretch factor of the item at position @a index to @a stretch.

simgear/canvas/layout/Layout.cxx

@@ -67,6 +67,13 @@ namespace canvas
     }
   }
 
+  //----------------------------------------------------------------------------
+  void Layout::clear()
+  {
+    while( itemAt(0) )
+      takeAt(0);
+  }
+
   //----------------------------------------------------------------------------
   void Layout::ItemData::reset()
   {

simgear/canvas/layout/Layout.hxx

@@ -66,6 +66,11 @@ namespace canvas
        */
       void removeItem(const LayoutItemRef& item);
 
+      /**
+       * Remove all items.
+       */
+      virtual void clear();
+
     protected:
       enum LayoutFlags
       {

simgear/canvas/layout/canvas_layout_test.cxx

@@ -309,6 +309,12 @@ BOOST_AUTO_TEST_CASE( boxlayout_insert_remove )
   hbox.removeItem(w2);
   BOOST_CHECK_EQUAL(hbox.count(), 1);
   BOOST_CHECK_EQUAL(hbox.itemAt(0), w1);
+
+  hbox.addItem(w2);
+  BOOST_CHECK_EQUAL(hbox.count(), 2);
+
+  hbox.clear();
+  BOOST_CHECK_EQUAL(hbox.count(), 0);
 }
 
 //------------------------------------------------------------------------------