Add `minetest.get_mapgen_edges` (#12999)

doc/lua_api.txt

@@ -5628,6 +5628,13 @@ Environment access
       prefix `"no"` is attached, clears instead.
     * `flags` is in the same format and has the same options as `mg_flags` in
       `minetest.conf`.
+* `minetest.get_mapgen_edges([mapgen_limit[, chunksize]])`
+    * Returns the minimum and maximum possible generated node positions
+      in that order.
+    * `mapgen_limit` is an optional number. If it is absent, its value is that
+      of the *active* mapgen setting `"mapgen_limit"`.
+    * `chunksize` is an optional number. If it is absent, its value is that
+      of the *active* mapgen setting `"chunksize"`.
 * `minetest.get_mapgen_setting(name)`
     * Gets the *active* mapgen setting (or nil if none exists) in string
       format with the following order of precedence:

games/devtest/mods/unittests/misc.lua

@@ -110,3 +110,40 @@ local function test_game_info()
 	assert(info.title == game_conf:get("title"))
 end
 unittests.register("test_game_info", test_game_info)
+
+local function test_mapgen_edges(cb)
+	-- Test that the map can extend to the expected edges and no further.
+	local min_edge, max_edge = minetest.get_mapgen_edges()
+	local min_finished = {}
+	local max_finished = {}
+	local function finish()
+		if #min_finished ~= 1 then
+			return cb("Expected 1 block to emerge around mapgen minimum edge")
+		end
+		if min_finished[1] ~= (min_edge / minetest.MAP_BLOCKSIZE):floor() then
+			return cb("Expected block within minimum edge to emerge")
+		end
+		if #max_finished ~= 1 then
+			return cb("Expected 1 block to emerge around mapgen maximum edge")
+		end
+		if max_finished[1] ~= (max_edge / minetest.MAP_BLOCKSIZE):floor() then
+			return cb("Expected block within maximum edge to emerge")
+		end
+		return cb()
+	end
+	local emerges_left = 2
+	local function emerge_block(blockpos, action, blocks_left, finished)
+		if action ~= minetest.EMERGE_CANCELLED then
+			table.insert(finished, blockpos)
+		end
+		if blocks_left == 0 then
+			emerges_left = emerges_left - 1
+			if emerges_left == 0 then
+				return finish()
+			end
+		end
+	end
+	minetest.emerge_area(min_edge:subtract(1), min_edge, emerge_block, min_finished)
+	minetest.emerge_area(max_edge, max_edge:add(1), emerge_block, max_finished)
+end
+unittests.register("test_mapgen_edges", test_mapgen_edges, {map=true, async=true})

src/mapgen/mapgen.cpp

@@ -1063,9 +1063,20 @@ void MapgenParams::writeParams(Settings *settings) const
 }
 
 
-// Calculate exact edges of the outermost mapchunks that are within the
-// set 'mapgen_limit'.
-void MapgenParams::calcMapgenEdges()
+s32 MapgenParams::getSpawnRangeMax()
+{
+	if (!m_mapgen_edges_calculated) {
+		std::pair<s16, s16> edges = get_mapgen_edges(mapgen_limit, chunksize);
+		mapgen_edge_min = edges.first;
+		mapgen_edge_max = edges.second;
+		m_mapgen_edges_calculated = true;
+	}
+
+	return MYMIN(-mapgen_edge_min, mapgen_edge_max);
+}
+
+
+std::pair<s16, s16> get_mapgen_edges(s16 mapgen_limit, s16 chunksize)
 {
 	// Central chunk offset, in blocks
 	s16 ccoff_b = -chunksize / 2;
@@ -1089,17 +1100,5 @@ void MapgenParams::calcMapgenEdges()
 	s16 numcmin = MYMAX((ccfmin - mapgen_limit_min) / csize_n, 0);
 	s16 numcmax = MYMAX((mapgen_limit_max - ccfmax) / csize_n, 0);
 	// Mapgen edges, in nodes
-	mapgen_edge_min = ccmin - numcmin * csize_n;
-	mapgen_edge_max = ccmax + numcmax * csize_n;
-
-	m_mapgen_edges_calculated = true;
-}
-
-
-s32 MapgenParams::getSpawnRangeMax()
-{
-	if (!m_mapgen_edges_calculated)
-		calcMapgenEdges();
-
-	return MYMIN(-mapgen_edge_min, mapgen_edge_max);
+	return std::pair<s16, s16>(ccmin - numcmin * csize_n, ccmax + numcmax * csize_n);
 }

src/mapgen/mapgen.h

@@ -25,6 +25,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "nodedef.h"
 #include "util/string.h"
 #include "util/container.h"
+#include <utility>
 
 #define MAPGEN_DEFAULT MAPGEN_V7
 #define MAPGEN_DEFAULT_NAME "v7"
@@ -139,7 +140,6 @@ struct MapgenParams {
 	s32 getSpawnRangeMax();
 
 private:
-	void calcMapgenEdges();
 	bool m_mapgen_edges_calculated = false;
 };
 
@@ -329,3 +329,7 @@ protected:
 	s16 dungeon_ymin;
 	s16 dungeon_ymax;
 };
+
+// Calculate exact edges of the outermost mapchunks that are within the set
+// mapgen_limit. Returns the minimum and maximum edges in nodes in that order.
+std::pair<s16, s16> get_mapgen_edges(s16 mapgen_limit, s16 chunksize);

src/script/lua_api/l_mapgen.cpp

@@ -810,6 +810,41 @@ int ModApiMapgen::l_set_mapgen_params(lua_State *L)
 	return 0;
 }
 
+// get_mapgen_edges([mapgen_limit[, chunksize]])
+int ModApiMapgen::l_get_mapgen_edges(lua_State *L)
+{
+	NO_MAP_LOCK_REQUIRED;
+
+	MapSettingsManager *settingsmgr = getServer(L)->getEmergeManager()->map_settings_mgr;
+
+	// MapSettingsManager::makeMapgenParams cannot be used here because it would
+	// make mapgen settings immutable from then on. Mapgen settings should stay
+	// mutable until after mod loading ends.
+
+	s16 mapgen_limit;
+	if (lua_isnumber(L, 1)) {
+		 mapgen_limit = lua_tointeger(L, 1);
+	} else {
+		std::string mapgen_limit_str;
+		settingsmgr->getMapSetting("mapgen_limit", &mapgen_limit_str);
+		mapgen_limit = stoi(mapgen_limit_str, 0, MAX_MAP_GENERATION_LIMIT);
+	}
+
+	s16 chunksize;
+	if (lua_isnumber(L, 2)) {
+		chunksize = lua_tointeger(L, 2);
+	} else {
+		std::string chunksize_str;
+		settingsmgr->getMapSetting("chunksize", &chunksize_str);
+		chunksize = stoi(chunksize_str, -32768, 32767);
+	}
+
+	std::pair<s16, s16> edges = get_mapgen_edges(mapgen_limit, chunksize);
+	push_v3s16(L, v3s16(1, 1, 1) * edges.first);
+	push_v3s16(L, v3s16(1, 1, 1) * edges.second);
+	return 2;
+}
+
 // get_mapgen_setting(name)
 int ModApiMapgen::l_get_mapgen_setting(lua_State *L)
 {
@@ -1782,6 +1817,7 @@ void ModApiMapgen::Initialize(lua_State *L, int top)
 
 	API_FCT(get_mapgen_params);
 	API_FCT(set_mapgen_params);
+	API_FCT(get_mapgen_edges);
 	API_FCT(get_mapgen_setting);
 	API_FCT(set_mapgen_setting);
 	API_FCT(get_mapgen_setting_noiseparams);

src/script/lua_api/l_mapgen.h

@@ -61,6 +61,9 @@ private:
 	// set mapgen parameters
 	static int l_set_mapgen_params(lua_State *L);
 
+	// get_mapgen_edges([mapgen_limit[, chunksize]])
+	static int l_get_mapgen_edges(lua_State *L);
+
 	// get_mapgen_setting(name)
 	static int l_get_mapgen_setting(lua_State *L);