Add find_surface_nodes_in_area LUA call which permit to only get the nodes which touch air. This permit to massively improve performance for mods like plantlife

doc/lua_api.txt

@@ -1869,6 +1869,9 @@ and `minetest.auth_reload` call the authetification handler.
     * `nodenames`: e.g. `{"ignore", "group:tree"}` or `"default:dirt"`
 * `minetest.find_nodes_in_area(minp, maxp, nodenames)`: returns a list of positions
     * `nodenames`: e.g. `{"ignore", "group:tree"}` or `"default:dirt"`
+* `minetest.find_surface_nodes_in_area(minp, maxp, nodenames)`: returns a list of positions
+    * returned positions are nodes with a node air above
+    * `nodenames`: e.g. `{"ignore", "group:tree"}` or `"default:dirt"`
 * `minetest.get_perlin(noiseparams)`
 * `minetest.get_perlin(seeddiff, octaves, persistence, scale)`
     * Return world-specific perlin noise (`int(worldseed)+seeddiff`)

src/script/lua_api/l_env.cpp

@@ -541,17 +541,17 @@ int ModApiEnvMod::l_find_nodes_in_area(lua_State *L)
 	v3s16 minp = read_v3s16(L, 1);
 	v3s16 maxp = read_v3s16(L, 2);
 	std::set<content_t> filter;
-	if(lua_istable(L, 3)){
+	if(lua_istable(L, 3)) {
 		int table = 3;
 		lua_pushnil(L);
-		while(lua_next(L, table) != 0){
+		while(lua_next(L, table) != 0) {
 			// key at index -2 and value at index -1
 			luaL_checktype(L, -1, LUA_TSTRING);
 			ndef->getIds(lua_tostring(L, -1), filter);
 			// removes value, keeps key for next iteration
 			lua_pop(L, 1);
 		}
-	} else if(lua_isstring(L, 3)){
+	} else if(lua_isstring(L, 3)) {
 		ndef->getIds(lua_tostring(L, 3), filter);
 	}
 
@@ -570,6 +570,51 @@ int ModApiEnvMod::l_find_nodes_in_area(lua_State *L)
 	return 1;
 }
 
+// find_surface_nodes_in_area(minp, maxp, nodenames) -> list of positions
+// nodenames: eg. {"ignore", "group:tree"} or "default:dirt"
+int ModApiEnvMod::l_find_surface_nodes_in_area(lua_State *L)
+{
+	GET_ENV_PTR;
+
+	INodeDefManager *ndef = getServer(L)->ndef();
+	v3s16 minp = read_v3s16(L, 1);
+	v3s16 maxp = read_v3s16(L, 2);
+	std::set<content_t> filter;
+	if(lua_istable(L, 3)) {
+		int table = 3;
+		lua_pushnil(L);
+		while(lua_next(L, table) != 0) {
+			// key at index -2 and value at index -1
+			luaL_checktype(L, -1, LUA_TSTRING);
+			ndef->getIds(lua_tostring(L, -1), filter);
+			// removes value, keeps key for next iteration
+			lua_pop(L, 1);
+		}
+	} else if(lua_isstring(L, 3)) {
+		ndef->getIds(lua_tostring(L, 3), filter);
+	}
+
+	lua_newtable(L);
+	u64 i = 0;
+	for(s16 x = minp.X; x <= maxp.X; x++)
+	for(s16 z = minp.Z; z <= maxp.Z; z++) {
+		s16 y = minp.Y;
+		v3s16 p(x, y, z);
+		content_t c = env->getMap().getNodeNoEx(p).getContent();
+		for(; y <= maxp.Y; y++) {
+			v3s16 psurf(x, y + 1, z);
+			content_t csurf = env->getMap().getNodeNoEx(psurf).getContent();
+			if(c != CONTENT_AIR && csurf == CONTENT_AIR &&
+					filter.count(c) != 0) {
+				push_v3s16(L, v3s16(x, y, z));
+				lua_rawseti(L, -2, ++i);
+			}
+			c = csurf;
+		}
+	}
+	return 1;
+}
+
 // get_perlin(seeddiff, octaves, persistence, scale)
 // returns world-specific PerlinNoise
 int ModApiEnvMod::l_get_perlin(lua_State *L)
@@ -867,6 +912,7 @@ void ModApiEnvMod::Initialize(lua_State *L, int top)
 	API_FCT(get_gametime);
 	API_FCT(find_node_near);
 	API_FCT(find_nodes_in_area);
+	API_FCT(find_surface_nodes_in_area);
 	API_FCT(delete_area);
 	API_FCT(get_perlin);
 	API_FCT(get_perlin_map);

src/script/lua_api/l_env.h

@@ -119,6 +119,10 @@ private:
 	// nodenames: eg. {"ignore", "group:tree"} or "default:dirt"
 	static int l_find_nodes_in_area(lua_State *L);
 
+	// find_surface_nodes_in_area(minp, maxp, nodenames) -> list of positions
+	// nodenames: eg. {"ignore", "group:tree"} or "default:dirt"
+	static int l_find_surface_nodes_in_area(lua_State *L);
+
 	// delete_area(p1, p2) -> true/false
 	static int l_delete_area(lua_State *L);