Backport 'Add min_y and max_y checks for Active Block Modifiers (ABM)' b10091be9b

This check can be used by ABM to reduce CPU usage.

doc/lua_api.txt

@@ -4238,6 +4238,12 @@ Definition tables
         ^ If left out or empty, any neighbor will do ]]
         interval = 1.0, -- Operation interval in seconds
         chance = 1, -- Chance of trigger per-node per-interval is 1.0 / this
+
+        min_y = -32768,
+        max_y = 32767,
+        -- min and max height levels where ABM will be processed
+        -- can be used to reduce CPU usage
+
         catch_up = true, -- If true, catch-up behaviour is enabled --[[
         ^ The chance value is temporarily reduced when returning to
           an area to simulate time lost by the area being unattended.

src/script/cpp_api/s_env.cpp

@@ -151,8 +151,14 @@ void ScriptApiEnv::initializeEnvironment(ServerEnvironment *env)
 		bool simple_catch_up = true;
 		getboolfield(L, current_abm, "catch_up", simple_catch_up);
 
+		int min_y = -32767;
+		getintfield(L, current_abm, "min_y", min_y);
+
+		int max_y = 32767;
+		getintfield(L, current_abm, "max_y", max_y);
+
 		LuaABM *abm = new LuaABM(L, id, trigger_contents, required_neighbors,
-			trigger_interval, trigger_chance, simple_catch_up);
+			trigger_interval, trigger_chance, simple_catch_up, min_y, max_y);
 
 		env->addActiveBlockModifier(abm);
 

src/script/lua_api/l_env.h

@@ -190,17 +190,21 @@ private:
 	float m_trigger_interval;
 	u32 m_trigger_chance;
 	bool m_simple_catch_up;
+	s16 m_min_y;
+	s16 m_max_y;
 public:
 	LuaABM(lua_State *L, int id,
 			const std::set<std::string> &trigger_contents,
 			const std::set<std::string> &required_neighbors,
-			float trigger_interval, u32 trigger_chance, bool simple_catch_up):
+			float trigger_interval, u32 trigger_chance, bool simple_catch_up, s16 min_y, s16 max_y):
 		m_id(id),
 		m_trigger_contents(trigger_contents),
 		m_required_neighbors(required_neighbors),
 		m_trigger_interval(trigger_interval),
 		m_trigger_chance(trigger_chance),
-		m_simple_catch_up(simple_catch_up)
+		m_simple_catch_up(simple_catch_up),
+		m_min_y(min_y),
+		m_max_y(max_y)
 	{
 	}
 	virtual const std::set<std::string> &getTriggerContents() const
@@ -223,6 +227,14 @@ public:
 	{
 		return m_simple_catch_up;
 	}
+	virtual s16 getMinY()
+	{
+		return m_min_y;
+	}
+	virtual s16 getMaxY()
+	{
+		return m_max_y;
+	}
 	virtual void trigger(ServerEnvironment *env, v3s16 p, MapNode n,
 			u32 active_object_count, u32 active_object_count_wider);
 };

src/serverenvironment.cpp

@@ -694,6 +694,9 @@ struct ActiveABM
 	ActiveBlockModifier *abm;
 	int chance;
 	std::set<content_t> required_neighbors;
+	bool check_required_neighbors; // false if required_neighbors is known to be empty
+	s16 min_y;
+	s16 max_y;
 };
 
 class ABMHandler
@@ -739,6 +742,9 @@ public:
 			} else {
 				aabm.chance = chance;
 			}
+			// y limits
+			aabm.min_y = abm->getMinY();
+			aabm.max_y = abm->getMaxY();
 
 			// Trigger neighbors
 			const std::set<std::string> &required_neighbors_s =
@@ -826,7 +832,10 @@ public:
 			v3s16 p = p0 + block->getPosRelative();
 			for(std::vector<ActiveABM>::iterator
 				i = m_aabms[c]->begin(); i != m_aabms[c]->end(); ++i) {
-				if(myrand() % i->chance != 0)
+				if ((p.Y < i->min_y) || (p.Y > i->max_y))
+					continue;
+
+				if (myrand() % i->chance != 0)
 					continue;
 
 				// Check neighbors

src/serverenvironment.h

@@ -62,6 +62,10 @@ public:
 	virtual u32 getTriggerChance() = 0;
 	// Whether to modify chance to simulate time lost by an unnattended block
 	virtual bool getSimpleCatchUp() = 0;
+	// get min Y for apply abm
+	virtual s16 getMinY() = 0;
+	// get max Y for apply abm
+	virtual s16 getMaxY() = 0;
 	// This is called usually at interval for 1/chance of the nodes
 	virtual void trigger(ServerEnvironment *env, v3s16 p, MapNode n){};
 	virtual void trigger(ServerEnvironment *env, v3s16 p, MapNode n,