Performance Improvement: Use a cache which caches result for getFacePositions.

This greatly reduce the number of std::list generated by caching the result, which is always constant for each radius selected.
In the callgrind map, you will see original:
  * 3.3M calls to std::list for 9700 calls to getFacePositions
In the modified version, you will see:
  * 3.3K calls to std::list for 6900 call to getFacePositions
Callgrind map is here: #2321

it's a huge performance improvement to l_find_node_near

1 files changed, 2 insertions, 3 deletions

diff --git a/src/script/lua_api/l_env.cpp b/src/script/lua_api/l_env.cpp
index cd5d253ac..2445803d7 100644
--- a/src/script/lua_api/l_env.cpp
+++ b/src/script/lua_api/l_env.cpp
@@ -530,9 +530,8 @@ int ModApiEnvMod::l_find_node_near(lua_State *L)
 	}
 
 	for(int d=1; d<=radius; d++){
-		std::list<v3s16> list;
-		getFacePositions(list, d);
-		for(std::list<v3s16>::iterator i = list.begin();
+		std::vector<v3s16> list = FacePositionCache::getFacePositions(d);
+		for(std::vector<v3s16>::iterator i = list.begin();
 				i != list.end(); ++i){
 			v3s16 p = pos + (*i);
 			content_t c = env->getMap().getNodeNoEx(p).getContent();