FindSpawnPos: Let mapgens decide what spawn altitude is suitable

To avoid spawn search failing in new specialised mapgens
Increase spawn search range to 4000 nodes
Add getSpawnLevelAtPoint() functions to EmergeManager, class Mapgen
and all mapgens
Remove getGroundLevelAtPoint() functions from all mapgens except mgv6
(possibly to be re-added later in the correct form to return actual
ground level)
Make mgvalleys flag names consistent with other mapgens
Remove now unused 'vertical spawn range' setting

Author: paramat

src/defaultsettings.cpp

@@ -247,7 +247,6 @@ void set_default_settings(Settings *settings)
 	settings->setDefault("default_privs", "interact, shout");
 	settings->setDefault("player_transfer_distance", "0");
 	settings->setDefault("enable_pvp", "true");
-	settings->setDefault("vertical_spawn_range", "16");
 	settings->setDefault("disallow_empty_password", "false");
 	settings->setDefault("disable_anticheat", "false");
 	settings->setDefault("enable_rollback_recording", "false");

src/emerge.cpp

@@ -334,6 +334,18 @@ v3s16 EmergeManager::getContainingChunk(v3s16 blockpos, s16 chunksize)
 }
 
 
+int EmergeManager::getSpawnLevelAtPoint(v2s16 p)
+{
+	if (m_mapgens.size() == 0 || !m_mapgens[0]) {
+		errorstream << "EmergeManager: getSpawnLevelAtPoint() called"
+			" before mapgen init" << std::endl;
+		return 0;
+	}
+
+	return m_mapgens[0]->getSpawnLevelAtPoint(p);
+}
+
+
 int EmergeManager::getGroundLevelAtPoint(v2s16 p)
 {
 	if (m_mapgens.size() == 0 || !m_mapgens[0]) {

src/emerge.h

@@ -136,6 +136,7 @@ class EmergeManager {
 
 	// Mapgen helpers methods
 	Biome *getBiomeAtPoint(v3s16 p);
+	int getSpawnLevelAtPoint(v2s16 p);
 	int getGroundLevelAtPoint(v2s16 p);
 	bool isBlockUnderground(v3s16 blockpos);
 

src/mapgen.h

@@ -181,6 +181,13 @@ class Mapgen {
 	virtual void makeChunk(BlockMakeData *data) {}
 	virtual int getGroundLevelAtPoint(v2s16 p) { return 0; }
 
+	// getSpawnLevelAtPoint() is a function within each mapgen that returns a
+	// suitable y co-ordinate for player spawn ('suitable' usually meaning
+	// within 16 nodes of water_level). If a suitable spawn level cannot be
+	// found at the specified (X, Z) 'MAX_MAP_GENERATION_LIMIT' is returned to
+	// signify this and to cause Server::findSpawnPos() to try another (X, Z).
+	virtual int getSpawnLevelAtPoint(v2s16 p) { return 0; }
+
 private:
 	DISABLE_CLASS_COPY(Mapgen);
 };

src/mapgen_flat.cpp

@@ -192,18 +192,25 @@ void MapgenFlatParams::writeParams(Settings *settings) const
 /////////////////////////////////////////////////////////////////
 
 
-int MapgenFlat::getGroundLevelAtPoint(v2s16 p)
+int MapgenFlat::getSpawnLevelAtPoint(v2s16 p)
 {
+	s16 level_at_point = ground_level;
 	float n_terrain = NoisePerlin2D(&noise_terrain->np, p.X, p.Y, seed);
+
 	if ((spflags & MGFLAT_LAKES) && n_terrain < lake_threshold) {
-		s16 depress = (lake_threshold - n_terrain) * lake_steepness;
-		return ground_level - depress;
+		level_at_point = ground_level -
+			(lake_threshold - n_terrain) * lake_steepness;
 	} else if ((spflags & MGFLAT_HILLS) && n_terrain > hill_threshold) {
-		s16 rise = (n_terrain - hill_threshold) * hill_steepness;
-		return ground_level + rise;
-	} else {
-		return ground_level;
+		level_at_point = ground_level +
+			(n_terrain - hill_threshold) * hill_steepness;
 	}
+
+	if (ground_level < water_level)  // Ocean world, allow spawn in water
+		return MYMAX(level_at_point, water_level);
+	else if (level_at_point > water_level)
+		return level_at_point;  // Spawn on land
+	else
+		return MAX_MAP_GENERATION_LIMIT;  // Unsuitable spawn point
 }
 
 

src/mapgen_flat.h

@@ -102,7 +102,7 @@ class MapgenFlat : public Mapgen {
 	~MapgenFlat();
 
 	virtual void makeChunk(BlockMakeData *data);
-	int getGroundLevelAtPoint(v2s16 p);
+	int getSpawnLevelAtPoint(v2s16 p);
 	void calculateNoise();
 	s16 generateTerrain();
 	MgStoneType generateBiomes(float *heat_map, float *humidity_map);

src/mapgen_fractal.cpp

@@ -209,17 +209,28 @@ void MapgenFractalParams::writeParams(Settings *settings) const
 /////////////////////////////////////////////////////////////////
 
 
-int MapgenFractal::getGroundLevelAtPoint(v2s16 p)
+int MapgenFractal::getSpawnLevelAtPoint(v2s16 p)
 {
-	s16 search_start = 128;
-	s16 search_end = -128;
-
-	for (s16 y = search_start; y >= search_end; y--) {
-		if (getFractalAtPoint(p.X, y, p.Y))
-			return y;
+	bool solid_below = false;  // Dry solid node is present below to spawn on
+	u8 air_count = 0;  // Consecutive air nodes above the dry solid node
+	s16 seabed_level = NoisePerlin2D(&noise_seabed->np, p.X, p.Y, seed);
+	// Seabed can rise above water_level or might be raised to create dry land
+	s16 search_start = MYMAX(seabed_level, water_level + 1);
+	if (seabed_level > water_level)
+		solid_below = true;
+		
+	for (s16 y = search_start; y <= search_start + 128; y++) {
+		if (getFractalAtPoint(p.X, y, p.Y)) {  // Fractal node
+			solid_below = true;
+			air_count = 0;
+		} else if (solid_below) {  // Air above solid node
+			air_count++;
+			if (air_count == 2)
+				return y - 2;
+		}
 	}
 
-	return -MAX_MAP_GENERATION_LIMIT;
+	return MAX_MAP_GENERATION_LIMIT;  // Unsuitable spawn point
 }
 
 

src/mapgen_fractal.h

@@ -114,7 +114,7 @@ class MapgenFractal : public Mapgen {
 	~MapgenFractal();
 
 	virtual void makeChunk(BlockMakeData *data);
-	int getGroundLevelAtPoint(v2s16 p);
+	int getSpawnLevelAtPoint(v2s16 p);
 	void calculateNoise();
 	bool getFractalAtPoint(s16 x, s16 y, s16 z);
 	s16 generateTerrain();

src/mapgen_singlenode.cpp

@@ -99,7 +99,7 @@ void MapgenSinglenode::makeChunk(BlockMakeData *data)
 }
 
 
-int MapgenSinglenode::getGroundLevelAtPoint(v2s16 p)
+int MapgenSinglenode::getSpawnLevelAtPoint(v2s16 p)
 {
 	return 0;
 }

src/mapgen_singlenode.h

@@ -41,7 +41,7 @@ class MapgenSinglenode : public Mapgen {
 	~MapgenSinglenode();
 
 	void makeChunk(BlockMakeData *data);
-	int getGroundLevelAtPoint(v2s16 p);
+	int getSpawnLevelAtPoint(v2s16 p);
 };
 
 struct MapgenFactorySinglenode : public MapgenFactory {