Mapgen flags: Add 'biomes' global mapgen flag (#7355)

Previously the only way to disable biomes was to 'clear' the registered
biomes in a mod, but this method causes large amounts of unnecessary
processing:
1. Calculation of 4 2D noises.
2. Looping through all nodes of a mapchunk replacing nodes with identical
nodes.
The new flag disables those operations.

9 files changed, 43 insertions, 19 deletions

diff --git a/src/mapgen/mapgen.cpp b/src/mapgen/mapgen.cpp
index dcdaf82c2..360afd897 100644
--- a/src/mapgen/mapgen.cpp
+++ b/src/mapgen/mapgen.cpp
@@ -56,7 +56,8 @@ FlagDesc flagdesc_mapgen[] = {
 	{"dungeons",    MG_DUNGEONS},
 	{"light",       MG_LIGHT},
 	{"decorations", MG_DECORATIONS},
-	{NULL,       0}
+	{"biomes",      MG_BIOMES},
+	{NULL,          0}
 };
 
 FlagDesc flagdesc_gennotify[] = {
diff --git a/src/mapgen/mapgen.h b/src/mapgen/mapgen.h
index abac79016..b60aea57e 100644
--- a/src/mapgen/mapgen.h
+++ b/src/mapgen/mapgen.h
@@ -36,6 +36,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #define MG_FLAT        0x08  // Deprecated. Moved into mgv6 flags
 #define MG_LIGHT       0x10
 #define MG_DECORATIONS 0x20
+#define MG_BIOMES      0x40
 
 typedef u8 biome_t;  // copy from mg_biome.h to avoid an unnecessary include
 
@@ -122,7 +123,7 @@ struct MapgenParams {
 	u64 seed = 0;
 	s16 water_level = 1;
 	s16 mapgen_limit = MAX_MAP_GENERATION_LIMIT;
-	u32 flags = MG_CAVES | MG_LIGHT | MG_DECORATIONS;
+	u32 flags = MG_CAVES | MG_LIGHT | MG_DECORATIONS | MG_BIOMES;
 
 	BiomeParams *bparams = nullptr;
 
diff --git a/src/mapgen/mapgen_carpathian.cpp b/src/mapgen/mapgen_carpathian.cpp
index 4347f8479..c1e07030c 100644
--- a/src/mapgen/mapgen_carpathian.cpp
+++ b/src/mapgen/mapgen_carpathian.cpp
@@ -247,8 +247,10 @@ void MapgenCarpathian::makeChunk(BlockMakeData *data)
 	updateHeightmap(node_min, node_max);
 
 	// Init biome generator, place biome-specific nodes, and build biomemap
-	biomegen->calcBiomeNoise(node_min);
-	generateBiomes();
+	if (flags & MG_BIOMES) {
+		biomegen->calcBiomeNoise(node_min);
+		generateBiomes();
+	}
 
 	// Generate tunnels, caverns and large randomwalk caves
 	if (flags & MG_CAVES) {
@@ -284,7 +286,8 @@ void MapgenCarpathian::makeChunk(BlockMakeData *data)
 	m_emerge->oremgr->placeAllOres(this, blockseed, node_min, node_max);
 
 	// Sprinkle some dust on top after everything else was generated
-	dustTopNodes();
+	if (flags & MG_BIOMES)
+		dustTopNodes();
 
 	// Update liquids
 	updateLiquid(&data->transforming_liquid, full_node_min, full_node_max);
diff --git a/src/mapgen/mapgen_flat.cpp b/src/mapgen/mapgen_flat.cpp
index dbe0bd5bb..e2bc42918 100644
--- a/src/mapgen/mapgen_flat.cpp
+++ b/src/mapgen/mapgen_flat.cpp
@@ -195,8 +195,10 @@ void MapgenFlat::makeChunk(BlockMakeData *data)
 	updateHeightmap(node_min, node_max);
 
 	// Init biome generator, place biome-specific nodes, and build biomemap
-	biomegen->calcBiomeNoise(node_min);
-	generateBiomes();
+	if (flags & MG_BIOMES) {
+		biomegen->calcBiomeNoise(node_min);
+		generateBiomes();
+	}
 
 	if (flags & MG_CAVES) {
 		// Generate tunnels
@@ -217,7 +219,8 @@ void MapgenFlat::makeChunk(BlockMakeData *data)
 	m_emerge->oremgr->placeAllOres(this, blockseed, node_min, node_max);
 
 	// Sprinkle some dust on top after everything else was generated
-	dustTopNodes();
+	if (flags & MG_BIOMES)
+		dustTopNodes();
 
 	//printf("makeChunk: %dms\n", t.stop());
 
diff --git a/src/mapgen/mapgen_fractal.cpp b/src/mapgen/mapgen_fractal.cpp
index a1d425cd0..b915cd8f9 100644
--- a/src/mapgen/mapgen_fractal.cpp
+++ b/src/mapgen/mapgen_fractal.cpp
@@ -206,8 +206,10 @@ void MapgenFractal::makeChunk(BlockMakeData *data)
 	updateHeightmap(node_min, node_max);
 
 	// Init biome generator, place biome-specific nodes, and build biomemap
-	biomegen->calcBiomeNoise(node_min);
-	generateBiomes();
+	if (flags & MG_BIOMES) {
+		biomegen->calcBiomeNoise(node_min);
+		generateBiomes();
+	}
 
 	if (flags & MG_CAVES) {
 		// Generate tunnels
@@ -228,7 +230,8 @@ void MapgenFractal::makeChunk(BlockMakeData *data)
 	m_emerge->oremgr->placeAllOres(this, blockseed, node_min, node_max);
 
 	// Sprinkle some dust on top after everything else was generated
-	dustTopNodes();
+	if (flags & MG_BIOMES)
+		dustTopNodes();
 
 	//printf("makeChunk: %dms\n", t.stop());
 
diff --git a/src/mapgen/mapgen_v5.cpp b/src/mapgen/mapgen_v5.cpp
index fc0970363..3be704cca 100644
--- a/src/mapgen/mapgen_v5.cpp
+++ b/src/mapgen/mapgen_v5.cpp
@@ -206,8 +206,10 @@ void MapgenV5::makeChunk(BlockMakeData *data)
 	updateHeightmap(node_min, node_max);
 
 	// Init biome generator, place biome-specific nodes, and build biomemap
-	biomegen->calcBiomeNoise(node_min);
-	generateBiomes();
+	if (flags & MG_BIOMES) {
+		biomegen->calcBiomeNoise(node_min);
+		generateBiomes();
+	}
 
 	// Generate tunnels, caverns and large randomwalk caves
 	if (flags & MG_CAVES) {
@@ -243,7 +245,8 @@ void MapgenV5::makeChunk(BlockMakeData *data)
 	m_emerge->oremgr->placeAllOres(this, blockseed, node_min, node_max);
 
 	// Sprinkle some dust on top after everything else was generated
-	dustTopNodes();
+	if (flags & MG_BIOMES)
+		dustTopNodes();
 
 	//printf("makeChunk: %dms\n", t.stop());
 
diff --git a/src/mapgen/mapgen_v7.cpp b/src/mapgen/mapgen_v7.cpp
index 610de4623..e266e29c8 100644
--- a/src/mapgen/mapgen_v7.cpp
+++ b/src/mapgen/mapgen_v7.cpp
@@ -326,8 +326,10 @@ void MapgenV7::makeChunk(BlockMakeData *data)
 	updateHeightmap(node_min, node_max);
 
 	// Init biome generator, place biome-specific nodes, and build biomemap
-	biomegen->calcBiomeNoise(node_min);
-	generateBiomes();
+	if (flags & MG_BIOMES) {
+		biomegen->calcBiomeNoise(node_min);
+		generateBiomes();
+	}
 
 	// Generate tunnels, caverns and large randomwalk caves
 	if (flags & MG_CAVES) {
@@ -363,7 +365,8 @@ void MapgenV7::makeChunk(BlockMakeData *data)
 	m_emerge->oremgr->placeAllOres(this, blockseed, node_min, node_max);
 
 	// Sprinkle some dust on top after everything else was generated
-	dustTopNodes();
+	if (flags & MG_BIOMES)
+		dustTopNodes();
 
 	// Update liquids
 	updateLiquid(&data->transforming_liquid, full_node_min, full_node_max);
diff --git a/src/mapgen/mapgen_valleys.cpp b/src/mapgen/mapgen_valleys.cpp
index 843acb690..341ce3137 100644
--- a/src/mapgen/mapgen_valleys.cpp
+++ b/src/mapgen/mapgen_valleys.cpp
@@ -231,7 +231,8 @@ void MapgenValleys::makeChunk(BlockMakeData *data)
 	updateHeightmap(node_min, node_max);
 
 	// Place biome-specific nodes and build biomemap
-	generateBiomes();
+	if (flags & MG_BIOMES)
+		generateBiomes();
 
 	// Generate tunnels, caverns and large randomwalk caves
 	if (flags & MG_CAVES) {
@@ -265,7 +266,8 @@ void MapgenValleys::makeChunk(BlockMakeData *data)
 	m_emerge->oremgr->placeAllOres(this, blockseed, node_min, node_max);
 
 	// Sprinkle some dust on top after everything else was generated
-	dustTopNodes();
+	if (flags & MG_BIOMES)
+		dustTopNodes();
 
 	updateLiquid(&data->transforming_liquid, full_node_min, full_node_max);
 
diff --git a/src/mapgen/mg_biome.cpp b/src/mapgen/mg_biome.cpp
index 42f762709..e02eee703 100644
--- a/src/mapgen/mg_biome.cpp
+++ b/src/mapgen/mg_biome.cpp
@@ -192,7 +192,12 @@ BiomeGenOriginal::BiomeGenOriginal(BiomeManager *biomemgr,
 
 	heatmap  = noise_heat->result;
 	humidmap = noise_humidity->result;
+
 	biomemap = new biome_t[m_csize.X * m_csize.Z];
+	// Initialise with the ID of the default biome so that cavegen can get
+	// biomes when biome generation (which calculates the biomemap IDs) is
+	// disabled.
+	memset(biomemap, 0, sizeof(biome_t) * m_csize.X * m_csize.Z);
 }
 
 BiomeGenOriginal::~BiomeGenOriginal()