Expose getPointedThing to Lua

This commit introduces Raycast, a Lua user object, which can be
used to perform a raycast on the map. The ray is continuable, so one can
also get hidden nodes (for example to see trough glass).

src/raycast.h

@@ -20,6 +20,49 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #ifndef SRC_RAYCAST_H_
 #define SRC_RAYCAST_H_
 
+#include "voxelalgorithms.h"
+#include "util/pointedthing.h"
+
+//! Sorts PointedThings based on their distance.
+struct RaycastSort
+{
+	bool operator() (const PointedThing &pt1, const PointedThing &pt2) const;
+};
+
+//! Describes the state of a raycast.
+class RaycastState
+{
+public:
+	/*!
+	 * Creates a raycast.
+	 * @param objects_pointable if false, only nodes will be found
+	 * @param liquids pointable if false, liquid nodes won't be found
+	 */
+	RaycastState(const core::line3d<f32> &shootline, bool objects_pointable,
+		bool liquids_pointable);
+
+	//! Shootline of the raycast.
+	core::line3d<f32> m_shootline;
+	//! Iterator to store the progress of the raycast.
+	voxalgo::VoxelLineIterator m_iterator;
+	//! Previous tested node during the raycast.
+	v3s16 m_previous_node;
+
+	/*!
+	 * This priority queue stores the found pointed things
+	 * waiting to be returned.
+	 */
+	std::priority_queue<PointedThing, std::vector<PointedThing>, RaycastSort> m_found;
+
+	bool m_objects_pointable;
+	bool m_liquids_pointable;
+
+	//! The code needs to search these nodes around the center node.
+	core::aabbox3d<s16> m_search_range { 0, 0, 0, 0, 0, 0 };
+
+	//! If true, the Environment will initialize this state.
+	bool m_initialization_needed = true;
+};
 
 /*!
  * Checks if a line and a box intersects.