Add the find_at functions for the pane.

This allows the usage of the mouse in the pane. Also increases the size
of the pane to have a bit more space to move the mouse around.

Note the offset to the mouse movement and what it affects on the screen
is intentionally.

The code is used to experiment with a different approach of the
implementation of a listbox.

data/gui/default/window/addon_list.cfg

@@ -392,6 +392,18 @@
 
 															[/column]
 
+															[column]
+																grow_factor = 0
+
+																horizontal_alignment = "right"
+																vertical_alignment = "bottom"
+																[toggle_button]
+																	id = "expand"
+																	definition = "default"
+																[/toggle_button]
+
+															[/column]
+
 														[/row]
 
 													[/grid]
@@ -406,15 +418,42 @@
 													vertical_grow = "true"
 													horizontal_grow = "true"
 
-													border = "all"
-													border_size = 5
+													[grid]
 
-													[label]
-														id = "description"
-														definition = "default"
+														[row]
 
-														characters_per_line = 66
-													[/label]
+															[column]
+																grow_factor = 1
+																vertical_grow = "true"
+																horizontal_grow = "true"
+
+																border = "all"
+																border_size = 5
+
+																[label]
+																	id = "description"
+																	definition = "default"
+
+																	characters_per_line = 66
+																[/label]
+
+															[/column]
+
+															[column]
+																grow_factor = 0
+
+																horizontal_alignment = "right"
+																vertical_alignment = "bottom"
+																[toggle_button]
+																	id = "collapse"
+																	definition = "default"
+																[/toggle_button]
+
+															[/column]
+
+														[/row]
+
+													[/grid]
 
 												[/column]
 

src/gui/widgets/pane.cpp

@@ -25,6 +25,81 @@
 
 namespace gui2 {
 
+/**
+ * Helper to implement private functions without modifying the header.
+ *
+ * The class is a helper to avoid recompilation and only has static
+ * functions. It also facilitates to create duplicates of functions for a const
+ * and a non-const member function.
+ */
+struct tpane_implementation
+{
+	/**
+	 * Implementation for the wrappers for
+	 * [const] twidget* tpane::find_at(const tpoint&, const bool) [const].
+	 *
+	 * @tparam W                  A pointer to the pane.
+	 */
+	template<class W>
+	static typename tconst_clone<twidget, W>::pointer
+	find_at(
+			  W pane
+			, tpoint coordinate
+			, const bool must_be_active
+			)
+	{
+
+		/*
+		 * First test whether the mouse is at the pane.
+		 */
+		if(pane->twidget::find_at(coordinate, must_be_active) != pane) {
+			return NULL;
+		}
+
+		/*
+		 * The widgets are placed at coordinate 0,0 so adjust the offset to
+		 * that coordinate system.
+		 */
+		coordinate.x -= pane->get_x();
+		coordinate.y -= pane->get_y();
+
+		typedef typename tconst_clone<tpane::titem, W>::reference thack;
+		BOOST_FOREACH(thack item, pane->items_) {
+
+			/*
+			 * If the adjusted coordinate is in the item's grid let the grid
+			 * resolve the coordinate.
+			 */
+			const SDL_Rect rect = item.grid->get_rect();
+			if(
+					   coordinate.x >= rect.x
+					&& coordinate.y >= rect.y
+					&& coordinate.x < rect.x + rect.w
+					&& coordinate.y < rect.y + rect.h) {
+
+				return item.grid->find_at(coordinate, must_be_active);
+			}
+
+			/*
+			 * No hit then adjust the coordinate with the size of the widget
+			 * that did not hit it. This is required since every item's grid
+			 * has its own coodinate systeme starting at 0,0.
+			 */
+			coordinate.y -= rect.h;
+
+			/*
+			 * If the position to test is outside our virtual area, we bail out.
+			 */
+			if(coordinate.y < 0) {
+				return NULL;
+			}
+		}
+
+		return NULL;
+	}
+};
+
+
 tpane::tpane(const tbuilder_grid_ptr item_builder)
 	: twidget()
 	, items_()
@@ -110,9 +185,29 @@ void tpane::request_reduce_width(const unsigned /*maximum_width*/)
 {
 }
 
+twidget* tpane::find_at(
+		  const tpoint& coordinate
+		, const bool must_be_active)
+{
+	return tpane_implementation::find_at(
+			  this
+			, coordinate
+			, must_be_active);
+}
+
+const twidget* tpane::find_at(
+		  const tpoint& coordinate
+		, const bool must_be_active) const
+{
+	return tpane_implementation::find_at(
+			  this
+			, coordinate
+			, must_be_active);
+}
+
 tpoint tpane::calculate_best_size() const
 {
-	return tpoint(100, 100);
+	return tpoint(500, 500);
 }
 
 bool tpane::disable_click_dismiss() const

src/gui/widgets/pane.hpp

@@ -30,6 +30,7 @@ class tgrid;
 class tpane
 	: public twidget
 {
+	friend struct tpane_implementation;
 public:
 
 	struct titem
@@ -75,6 +76,14 @@ public:
 	/** Inherited from twidget. */
 	void request_reduce_width(const unsigned maximum_width);
 
+	/** Inherited from twidget. */
+	twidget* find_at(const tpoint& coordinate, const bool must_be_active);
+
+	/** Inherited from twidget. */
+	const twidget* find_at(
+			const tpoint& coordinate,
+			const bool must_be_active) const;
+
 	/**
 	 * Sorts the contents of the pane.
 	 *