4 files changed, 134 insertions, 0 deletions

diff --git a/src/script/lua_api/l_env.cpp b/src/script/lua_api/l_env.cpp
index 138e88ae8..8d50d664d 100644
--- a/src/script/lua_api/l_env.cpp
+++ b/src/script/lua_api/l_env.cpp
@@ -407,6 +407,46 @@ int ModApiEnvMod::l_get_node_light(lua_State *L)
 	return 1;
 }
 
+
+// get_natural_light(pos, timeofday)
+// pos = {x=num, y=num, z=num}
+// timeofday: nil = current time, 0 = night, 0.5 = day
+int ModApiEnvMod::l_get_natural_light(lua_State *L)
+{
+	GET_ENV_PTR;
+
+	v3s16 pos = read_v3s16(L, 1);
+
+	bool is_position_ok;
+	MapNode n = env->getMap().getNode(pos, &is_position_ok);
+	if (!is_position_ok)
+		return 0;
+
+	// If the daylight is 0, nothing needs to be calculated
+	u8 daylight = n.param1 & 0x0f;
+	if (daylight == 0) {
+		lua_pushinteger(L, 0);
+		return 1;
+	}
+
+	u32 time_of_day;
+	if (lua_isnumber(L, 2)) {
+		time_of_day = 24000.0 * lua_tonumber(L, 2);
+		time_of_day %= 24000;
+	} else {
+		time_of_day = env->getTimeOfDay();
+	}
+	u32 dnr = time_to_daynight_ratio(time_of_day, true);
+
+	// If it's the same as the artificial light, the sunlight needs to be
+	// searched for because the value may not emanate from the sun
+	if (daylight == n.param1 >> 4)
+		daylight = env->findSunlight(pos);
+
+	lua_pushinteger(L, dnr * daylight / 1000);
+	return 1;
+}
+
 // place_node(pos, node)
 // pos = {x=num, y=num, z=num}
 int ModApiEnvMod::l_place_node(lua_State *L)
@@ -1358,6 +1398,7 @@ void ModApiEnvMod::Initialize(lua_State *L, int top)
 	API_FCT(get_node);
 	API_FCT(get_node_or_nil);
 	API_FCT(get_node_light);
+	API_FCT(get_natural_light);
 	API_FCT(place_node);
 	API_FCT(dig_node);
 	API_FCT(punch_node);
diff --git a/src/script/lua_api/l_env.h b/src/script/lua_api/l_env.h
index 07d4d2438..7f212b5fc 100644
--- a/src/script/lua_api/l_env.h
+++ b/src/script/lua_api/l_env.h
@@ -56,6 +56,11 @@ private:
 	// timeofday: nil = current time, 0 = night, 0.5 = day
 	static int l_get_node_light(lua_State *L);
 
+	// get_natural_light(pos, timeofday)
+	// pos = {x=num, y=num, z=num}
+	// timeofday: nil = current time, 0 = night, 0.5 = day
+	static int l_get_natural_light(lua_State *L);
+
 	// place_node(pos, node)
 	// pos = {x=num, y=num, z=num}
 	static int l_place_node(lua_State *L);
diff --git a/src/serverenvironment.cpp b/src/serverenvironment.cpp
index 320042e19..6ef56efc8 100644
--- a/src/serverenvironment.cpp
+++ b/src/serverenvironment.cpp
@@ -1066,6 +1066,91 @@ bool ServerEnvironment::swapNode(v3s16 p, const MapNode &n)
 	return true;
 }
 
+u8 ServerEnvironment::findSunlight(v3s16 pos) const
+{
+	// Directions for neighbouring nodes with specified order
+	static const v3s16 dirs[] = {
+		v3s16(-1, 0, 0), v3s16(1, 0, 0), v3s16(0, 0, -1), v3s16(0, 0, 1),
+		v3s16(0, -1, 0), v3s16(0, 1, 0)
+	};
+
+	const NodeDefManager *ndef = m_server->ndef();
+
+	// found_light remembers the highest known sunlight value at pos
+	u8 found_light = 0;
+
+	struct stack_entry {
+		v3s16 pos;
+		s16 dist;
+	};
+	std::stack<stack_entry> stack;
+	stack.push({pos, 0});
+
+	std::unordered_map<s64, s8> dists;
+	dists[MapDatabase::getBlockAsInteger(pos)] = 0;
+
+	while (!stack.empty()) {
+		struct stack_entry e = stack.top();
+		stack.pop();
+
+		v3s16 currentPos = e.pos;
+		s8 dist = e.dist + 1;
+
+		for (const v3s16& off : dirs) {
+			v3s16 neighborPos = currentPos + off;
+			s64 neighborHash = MapDatabase::getBlockAsInteger(neighborPos);
+
+			// Do not walk neighborPos multiple times unless the distance to the start
+			// position is shorter
+			auto it = dists.find(neighborHash);
+			if (it != dists.end() && dist >= it->second)
+				continue;
+
+			// Position to walk
+			bool is_position_ok;
+			MapNode node = m_map->getNode(neighborPos, &is_position_ok);
+			if (!is_position_ok) {
+				// This happens very rarely because the map at currentPos is loaded
+				m_map->emergeBlock(neighborPos, false);
+				node = m_map->getNode(neighborPos, &is_position_ok);
+				if (!is_position_ok)
+					continue;  // not generated
+			}
+
+			const ContentFeatures &def = ndef->get(node);
+			if (!def.sunlight_propagates) {
+				// Do not test propagation here again
+				dists[neighborHash] = -1;
+				continue;
+			}
+
+			// Sunlight could have come from here
+			dists[neighborHash] = dist;
+			u8 daylight = node.param1 & 0x0f;
+
+			// In the special case where sunlight shines from above and thus
+			// does not decrease with upwards distance, daylight is always
+			// bigger than nightlight, which never reaches 15
+			int possible_finlight = daylight - dist;
+			if (possible_finlight <= found_light) {
+				// Light from here cannot make a brighter light at currentPos than
+				// found_light
+				continue;
+			}
+
+			u8 nightlight = node.param1 >> 4;
+			if (daylight > nightlight) {
+				// Found a valid daylight
+				found_light = possible_finlight;
+			} else {
+				// Sunlight may be darker, so walk the neighbours
+				stack.push({neighborPos, dist});
+			}
+		}
+	}
+	return found_light;
+}
+
 void ServerEnvironment::clearObjects(ClearObjectsMode mode)
 {
 	infostream << "ServerEnvironment::clearObjects(): "
diff --git a/src/serverenvironment.h b/src/serverenvironment.h
index af742e290..cfd5b8f3e 100644
--- a/src/serverenvironment.h
+++ b/src/serverenvironment.h
@@ -322,6 +322,9 @@ public:
 	bool removeNode(v3s16 p);
 	bool swapNode(v3s16 p, const MapNode &n);
 
+	// Find the daylight value at pos with a Depth First Search
+	u8 findSunlight(v3s16 pos) const;
+
 	// Find all active objects inside a radius around a point
 	void getObjectsInsideRadius(std::vector<ServerActiveObject *> &objects, const v3f &pos, float radius,
 			std::function<bool(ServerActiveObject *obj)> include_obj_cb)