Add API for mods to hook liquid transformation events (#11405)

Add API for mods to hook liquid transformation events

Without this API, there is no reliable way for mods to be
notified when liquid transform modifies nodes and mods are
forced to poll for changes.  This allows mods to detect
changes to flowing liquid nodes and liquid renewal using
event-driven logic.

src/map.cpp

@@ -829,7 +829,7 @@ void Map::transformLiquids(std::map<v3s16, MapBlock*> &modified_blocks,
 		m_transforming_liquid.push_back(iter);
 
 	voxalgo::update_lighting_nodes(this, changed_nodes, modified_blocks);
-
+	env->getScriptIface()->on_liquid_transformed(changed_nodes);
 
 	/* ----------------------------------------------------------------------
 	 * Manage the queue so that it does not grow indefinately

src/script/cpp_api/s_env.cpp

@@ -25,6 +25,8 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "mapgen/mapgen.h"
 #include "lua_api/l_env.h"
 #include "server.h"
+#include "script/common/c_content.h"
+
 
 void ScriptApiEnv::environment_OnGenerated(v3s16 minp, v3s16 maxp,
 	u32 blockseed)
@@ -267,3 +269,35 @@ void ScriptApiEnv::on_emerge_area_completion(
 		luaL_unref(L, LUA_REGISTRYINDEX, state->args_ref);
 	}
 }
+
+void ScriptApiEnv::on_liquid_transformed(
+	const std::vector<std::pair<v3s16, MapNode>> &list)
+{
+	SCRIPTAPI_PRECHECKHEADER
+
+	// Get core.registered_on_liquid_transformed
+	lua_getglobal(L, "core");
+	lua_getfield(L, -1, "registered_on_liquid_transformed");
+	luaL_checktype(L, -1, LUA_TTABLE);
+	lua_remove(L, -2);
+
+	// Skip converting list and calling hook if there are
+	// no registered callbacks.
+	if(lua_objlen(L, -1) < 1) return;
+
+	// Convert the list to a pos array and a node array for lua
+	int index = 1;
+	const NodeDefManager *ndef = getEnv()->getGameDef()->ndef();
+	lua_createtable(L, list.size(), 0);
+	lua_createtable(L, list.size(), 0);
+	for(std::pair<v3s16, MapNode> p : list) {
+		lua_pushnumber(L, index);
+		push_v3s16(L, p.first);
+		lua_rawset(L, -4);
+		lua_pushnumber(L, index++);
+		pushnode(L, p.second, ndef);
+		lua_rawset(L, -3);
+	}
+
+	runCallbacks(2, RUN_CALLBACKS_MODE_FIRST);
+}

src/script/cpp_api/s_env.h

@@ -21,6 +21,8 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 
 #include "cpp_api/s_base.h"
 #include "irr_v3d.h"
+#include "mapnode.h"
+#include <vector>
 
 class ServerEnvironment;
 struct ScriptCallbackState;
@@ -41,5 +43,8 @@ public:
 	void on_emerge_area_completion(v3s16 blockpos, int action,
 		ScriptCallbackState *state);
 
+	// Called after liquid transform changes
+	void on_liquid_transformed(const std::vector<std::pair<v3s16, MapNode>> &list);
+
 	void initializeEnvironment(ServerEnvironment *env);
 };