Dungeongen: Remove most hardcoded dungeon nodes (#8594)

Biome-defined dungeon nodes was added as a feature to MT 5.0.0.
So now remove most of the hardcoded dungeon node code that assumes a
game has stone, sandstone, desert stone, and no other stone types.
If biome-defined dungeon nodes are not found, dungeon nodes fall back
to the 'cobble' mapgen alias if present, if not present they fall back
to biome-defined 'stone'.
Remove now-unnecessary mapgen aliases from MapgenBasic. Non-mgv6 games
now only need to define 3 to 5 mapgen aliases.

Document dungeon parameters.

Make c_lava_source fallback to c_water_source as both are used as cave
liquids.

4 files changed, 45 insertions, 121 deletions

diff --git a/doc/lua_api.txt b/doc/lua_api.txt
index d881c4ef1..a25ada768 100644
--- a/doc/lua_api.txt
+++ b/doc/lua_api.txt
@@ -282,36 +282,26 @@ Mapgen aliases
 --------------
 
 In a game, a certain number of these must be set to tell core mapgens which
-of the game's nodes are to be used by the core mapgens. For example:
+of the game's nodes are to be used for core mapgen generation. For example:
 
     minetest.register_alias("mapgen_stone", "default:stone")
 
 ### Aliases needed for all mapgens except Mapgen V6
 
-#### Base terrain
-
 * mapgen_stone
 * mapgen_water_source
 * mapgen_river_water_source
 
-#### Caves
+`mapgen_river_water_source` is required for mapgens with sloping rivers where
+it is necessary to have a river liquid node with a short `liquid_range` and
+`liquid_renewable = false` to avoid flooding.
 
-Not required if cave liquid nodes are set in biome definitions.
+#### Deprecated aliases
 
 * mapgen_lava_source
-
-#### Dungeons
-
-Not required if dungeon nodes are set in biome definitions.
-
 * mapgen_cobble
-* mapgen_stair_cobble
-* mapgen_mossycobble
-* mapgen_desert_stone
-* mapgen_stair_desert_stone
-* mapgen_sandstone
-* mapgen_sandstonebrick
-* mapgen_stair_sandstone_block
+
+Use biome-defined cave liquids and dungeon nodes instead.
 
 ### Aliases needed for Mapgen V6
 
diff --git a/src/mapgen/dungeongen.h b/src/mapgen/dungeongen.h
index 2c20446fd..7b476527b 100644
--- a/src/mapgen/dungeongen.h
+++ b/src/mapgen/dungeongen.h
@@ -42,22 +42,35 @@ struct DungeonParams {
 	s32 seed;
 
 	content_t c_wall;
+	// Randomly scattered alternative wall nodes
 	content_t c_alt_wall;
 	content_t c_stair;
 
+	// Diagonal corridors are possible
 	bool diagonal_dirs;
+	// Dungeon only generates in ground
 	bool only_in_ground;
+	// Dimensions of 3D 'brush' that creates corridors.
+	// Dimensions are of the empty space, not including walls / floor / ceilng.
 	v3s16 holesize;
+	// Corridor length
 	u16 corridor_len_min;
 	u16 corridor_len_max;
+	// Room size includes walls / floor / ceilng
 	v3s16 room_size_min;
 	v3s16 room_size_max;
+	// The 1st room generated has a 1 in 4 chance of being 'large', all other
+	// rooms are not 'large'.
 	v3s16 room_size_large_min;
 	v3s16 room_size_large_max;
+	// Number of rooms
 	u16 rooms_min;
 	u16 rooms_max;
+	// Usually 'GENNOTIFY_DUNGEON', but mapgen v6 uses 'GENNOTIFY_TEMPLE' for
+	// desert dungeons.
 	GenNotifyType notifytype;
 
+	// 3D noise that determines which c_wall nodes are converted to c_alt_wall
 	NoiseParams np_alt_wall;
 };
 
diff --git a/src/mapgen/mapgen.cpp b/src/mapgen/mapgen.cpp
index c4aaff00d..838253a75 100644
--- a/src/mapgen/mapgen.cpp
+++ b/src/mapgen/mapgen.cpp
@@ -593,45 +593,20 @@ MapgenBasic::MapgenBasic(int mapgenid, MapgenParams *params, EmergeManager *emer
 	this->heightmap = new s16[csize.X * csize.Z];
 
 	//// Initialize biome generator
-	// TODO(hmmmm): should we have a way to disable biomemanager biomes?
 	biomegen = m_bmgr->createBiomeGen(BIOMEGEN_ORIGINAL, params->bparams, csize);
 	biomemap = biomegen->biomemap;
 
 	//// Look up some commonly used content
 	c_stone              = ndef->getId("mapgen_stone");
-	c_desert_stone       = ndef->getId("mapgen_desert_stone");
-	c_sandstone          = ndef->getId("mapgen_sandstone");
 	c_water_source       = ndef->getId("mapgen_water_source");
 	c_river_water_source = ndef->getId("mapgen_river_water_source");
 	c_lava_source        = ndef->getId("mapgen_lava_source");
+	c_cobble             = ndef->getId("mapgen_cobble");
 
-	// Fall back to more basic content if not defined
-	// river_water_source cannot fallback to water_source because river water
-	// needs to be non-renewable and have a short flow range.
-	if (c_desert_stone == CONTENT_IGNORE)
-		c_desert_stone = c_stone;
-	if (c_sandstone == CONTENT_IGNORE)
-		c_sandstone = c_stone;
-
-	//// Content used for dungeon generation
-	c_cobble                = ndef->getId("mapgen_cobble");
-	c_mossycobble           = ndef->getId("mapgen_mossycobble");
-	c_stair_cobble          = ndef->getId("mapgen_stair_cobble");
-	c_stair_desert_stone    = ndef->getId("mapgen_stair_desert_stone");
-	c_sandstonebrick        = ndef->getId("mapgen_sandstonebrick");
-	c_stair_sandstone_block = ndef->getId("mapgen_stair_sandstone_block");
-
-	// Fall back to more basic content if not defined
-	if (c_mossycobble == CONTENT_IGNORE)
-		c_mossycobble = c_cobble;
-	if (c_stair_cobble == CONTENT_IGNORE)
-		c_stair_cobble = c_cobble;
-	if (c_stair_desert_stone == CONTENT_IGNORE)
-		c_stair_desert_stone = c_desert_stone;
-	if (c_sandstonebrick == CONTENT_IGNORE)
-		c_sandstonebrick = c_sandstone;
-	if (c_stair_sandstone_block == CONTENT_IGNORE)
-		c_stair_sandstone_block = c_sandstonebrick;
+	// Fall back to more basic content if not defined.
+	// Lava falls back to water as both are suitable as cave liquids.
+	if (c_lava_source == CONTENT_IGNORE)
+		c_lava_source = c_water_source;
 }
 
 
@@ -911,78 +886,34 @@ void MapgenBasic::generateDungeons(s16 max_stone_y)
 	dp.np_alt_wall = 
 		NoiseParams(-0.4, 1.0, v3f(40.0, 40.0, 40.0), 32474, 6, 1.1, 2.0);
 
-	// Biome-defined dungeon nodes
+	dp.diagonal_dirs       = false;
+	dp.holesize            = v3s16(2, 3, 2);
+	dp.room_size_min       = v3s16(6, 5, 6);
+	dp.room_size_max       = v3s16(10, 6, 10);
+	dp.room_size_large_min = v3s16(10, 8, 10);
+	dp.room_size_large_max = v3s16(18, 16, 18);
+	dp.notifytype          = GENNOTIFY_DUNGEON;
+
+	// Use biome-defined dungeon nodes if defined
 	if (biome->c_dungeon != CONTENT_IGNORE) {
-		dp.c_wall              = biome->c_dungeon;
+		dp.c_wall = biome->c_dungeon;
 		// If 'node_dungeon_alt' is not defined by biome, it and dp.c_alt_wall
 		// become CONTENT_IGNORE which skips the alt wall node placement loop in
 		// dungeongen.cpp.
-		dp.c_alt_wall          = biome->c_dungeon_alt;
+		dp.c_alt_wall = biome->c_dungeon_alt;
 		// Stairs fall back to 'c_dungeon' if not defined by biome
 		dp.c_stair = (biome->c_dungeon_stair != CONTENT_IGNORE) ?
 			biome->c_dungeon_stair : biome->c_dungeon;
-
-		dp.diagonal_dirs       = false;
-		dp.holesize            = v3s16(2, 2, 2);
-		dp.room_size_min       = v3s16(6, 4, 6);
-		dp.room_size_max       = v3s16(10, 6, 10);
-		dp.room_size_large_min = v3s16(10, 8, 10);
-		dp.room_size_large_max = v3s16(18, 16, 18);
-		dp.notifytype          = GENNOTIFY_DUNGEON;
-
-	// Otherwise classic behaviour
-	} else if (biome->c_stone == c_stone) {
-		dp.c_wall              = c_cobble;
-		dp.c_alt_wall          = c_mossycobble;
-		dp.c_stair             = c_stair_cobble;
-
-		dp.diagonal_dirs       = false;
-		dp.holesize            = v3s16(1, 2, 1);
-		dp.room_size_min       = v3s16(4, 4, 4);
-		dp.room_size_max       = v3s16(8, 6, 8);
-		dp.room_size_large_min = v3s16(8, 8, 8);
-		dp.room_size_large_max = v3s16(16, 16, 16);
-		dp.notifytype          = GENNOTIFY_DUNGEON;
-
-	} else if (biome->c_stone == c_desert_stone) {
-		dp.c_wall              = c_desert_stone;
-		dp.c_alt_wall          = CONTENT_IGNORE;
-		dp.c_stair             = c_stair_desert_stone;
-
-		dp.diagonal_dirs       = true;
-		dp.holesize            = v3s16(2, 3, 2);
-		dp.room_size_min       = v3s16(6, 9, 6);
-		dp.room_size_max       = v3s16(10, 11, 10);
-		dp.room_size_large_min = v3s16(10, 13, 10);
-		dp.room_size_large_max = v3s16(18, 21, 18);
-		dp.notifytype          = GENNOTIFY_TEMPLE;
-
-	} else if (biome->c_stone == c_sandstone) {
-		dp.c_wall              = c_sandstonebrick;
-		dp.c_alt_wall          = CONTENT_IGNORE;
-		dp.c_stair             = c_stair_sandstone_block;
-
-		dp.diagonal_dirs       = false;
-		dp.holesize            = v3s16(2, 2, 2);
-		dp.room_size_min       = v3s16(6, 4, 6);
-		dp.room_size_max       = v3s16(10, 6, 10);
-		dp.room_size_large_min = v3s16(10, 8, 10);
-		dp.room_size_large_max = v3s16(18, 16, 18);
-		dp.notifytype          = GENNOTIFY_DUNGEON;
-
-	// Fallback to using biome 'node_stone'
+	// Fallback to using cobble mapgen alias if defined
+	} else if (c_cobble != CONTENT_IGNORE) {
+		dp.c_wall     = c_cobble;
+		dp.c_alt_wall = CONTENT_IGNORE;
+		dp.c_stair    = c_cobble;
+	// Fallback to using biome-defined stone
 	} else {
-		dp.c_wall              = biome->c_stone;
-		dp.c_alt_wall          = CONTENT_IGNORE;
-		dp.c_stair             = biome->c_stone;
-
-		dp.diagonal_dirs       = false;
-		dp.holesize            = v3s16(2, 2, 2);
-		dp.room_size_min       = v3s16(6, 4, 6);
-		dp.room_size_max       = v3s16(10, 6, 10);
-		dp.room_size_large_min = v3s16(10, 8, 10);
-		dp.room_size_large_max = v3s16(18, 16, 18);
-		dp.notifytype          = GENNOTIFY_DUNGEON;
+		dp.c_wall     = biome->c_stone;
+		dp.c_alt_wall = CONTENT_IGNORE;
+		dp.c_stair    = biome->c_stone;
 	}
 
 	DungeonGen dgen(ndef, &gennotify, &dp);
diff --git a/src/mapgen/mapgen.h b/src/mapgen/mapgen.h
index 2fc3aed95..f98c3f377 100644
--- a/src/mapgen/mapgen.h
+++ b/src/mapgen/mapgen.h
@@ -257,21 +257,11 @@ protected:
 	v3s16 full_node_min;
 	v3s16 full_node_max;
 
-	// Content required for generateBiomes
 	content_t c_stone;
-	content_t c_desert_stone;
-	content_t c_sandstone;
 	content_t c_water_source;
 	content_t c_river_water_source;
 	content_t c_lava_source;
-
-	// Content required for generateDungeons
 	content_t c_cobble;
-	content_t c_stair_cobble;
-	content_t c_mossycobble;
-	content_t c_stair_desert_stone;
-	content_t c_sandstonebrick;
-	content_t c_stair_sandstone_block;
 
 	int ystride;
 	int zstride;