Improved lighting

This commit rewrites the procedure that is responsible for light
updating.

this commit
-provides iterative solutions for unlighting and light spreading
-introduces a new priority queue-like container for the iteration
-creates per-node MapBlock caching to reduce retrieving MapBlocks from
the map
-calculates with map block positions and in-block relative node
coordinates
-skips light updating if it is not necessary since the node's new light
will be the same as its old light was

src/voxelalgorithms.h

@@ -25,6 +25,9 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include <set>
 #include <map>
 
+class Map;
+class MapBlock;
+
 namespace voxalgo
 {
 
@@ -52,6 +55,23 @@ SunlightPropagateResult propagateSunlight(VoxelManipulator &v, VoxelArea a,
 		std::set<v3s16> & light_sources,
 		INodeDefManager *ndef);
 
+/*!
+ * Updates the lighting on the map.
+ * The result will be correct only if
+ * no nodes were changed except the given one.
+ *
+ * \param p position of the changed node
+ * \param oldnode this node was overwritten on the map
+ * \param modified_blocks output, contains all map blocks that
+ * the function modified
+ */
+void update_lighting_node(
+	Map *map,
+	INodeDefManager *ndef,
+	v3s16 p,
+	MapNode oldnode,
+	std::map<v3s16, MapBlock*> &modified_blocks);
+
 } // namespace voxalgo
 
 #endif