Dungeons: Add setting to prevent projecting dungeons

Prevents dungeons generating into ignore nodes in ungenerated mapchunks,
which can occasionally result in a dungeon projecting from the terrain.

builtin/settingtypes.txt

@@ -984,6 +984,9 @@ mapgen_limit (Map generation limit) int 31000 0 31000
 #    Flags starting with 'no' are used to explicitly disable them.
 mg_flags (Mapgen flags) flags caves,dungeons,light,decorations caves,dungeons,light,decorations,nocaves,nodungeons,nolight,nodecorations
 
+#    Whether dungeons occasionally project from the terrain.
+projecting_dungeons (Projecting dungeons) bool true
+
 [**Advanced]
 
 #    Size of chunks to be generated at once by mapgen, stated in mapblocks (16 nodes).

minetest.conf.example

@@ -1201,6 +1201,10 @@
 #    type: flags possible values: caves, dungeons, light, decorations, nocaves, nodungeons, nolight, nodecorations
 # mg_flags = caves,dungeons,light,decorations
 
+#    Whether dungeons occasionally project from the terrain.
+#    type: bool
+# projecting_dungeons = true
+
 ### Advanced
 
 #    Size of chunks to be generated at once by mapgen, stated in mapblocks (16 nodes).

src/defaultsettings.cpp

@@ -349,6 +349,7 @@ void set_default_settings(Settings *settings)
 	settings->setDefault("mg_flags", "dungeons");
 	settings->setDefault("fixed_map_seed", "");
 	settings->setDefault("max_block_generate_distance", "7");
+	settings->setDefault("projecting_dungeons", "true");
 	settings->setDefault("enable_mapgen_debug_info", "false");
 
 	// Server list announcing

src/dungeongen.cpp

@@ -97,6 +97,8 @@ void DungeonGen::generate(MMVManip *vm, u32 bseed, v3s16 nmin, v3s16 nmax)
 	if (nval_density < 1.0f)
 		return;
 
+	static const bool preserve_ignore = !g_settings->getBool("projecting_dungeons");
+
 	this->vm = vm;
 	this->blockseed = bseed;
 	random.seed(bseed + 2);
@@ -105,14 +107,16 @@ void DungeonGen::generate(MMVManip *vm, u32 bseed, v3s16 nmin, v3s16 nmax)
 	vm->clearFlag(VMANIP_FLAG_DUNGEON_INSIDE | VMANIP_FLAG_DUNGEON_PRESERVE);
 
 	if (dp.only_in_ground) {
-		// Set all air and water to be untouchable
+		// Set all air and water to be untouchable to make dungeons open to
-		// to make dungeons open to caves and open air
+		// caves and open air. Optionally set ignore to be untouchable to
+		// prevent protruding dungeons.
 		for (s16 z = nmin.Z; z <= nmax.Z; z++) {
 			for (s16 y = nmin.Y; y <= nmax.Y; y++) {
 				u32 i = vm->m_area.index(nmin.X, y, z);
 				for (s16 x = nmin.X; x <= nmax.X; x++) {
 					content_t c = vm->m_data[i].getContent();
 					if (c == CONTENT_AIR || c == dp.c_water ||
+							(preserve_ignore && c == CONTENT_IGNORE) ||
 							c == dp.c_river_water)
 						vm->m_flags[i] |= VMANIP_FLAG_DUNGEON_PRESERVE;
 					i++;