Add new Mapgen V7 floatland implementation (#9296)

Floatland structure is vertically-compressed 3D noise.
Uses a lacunarity of 1.618 (the golden ratio) for high quality
noise.
Floatlands appear between user-settable Y limits, with smooth
tapering at each limit.
Simple user-settable density adjustment.
Shadow propagation is disabled in and just below floatlands, no
shadows are cast on the world surface.
Can be reconfigured to create a solid upper world layer between
the Y limits, lakes/seas can be optionally added to this.

3 files changed, 160 insertions, 12 deletions

diff --git a/builtin/settingtypes.txt b/builtin/settingtypes.txt
index b75bf2de5..d3f2c60b5 100644
--- a/builtin/settingtypes.txt
+++ b/builtin/settingtypes.txt
@@ -1607,12 +1607,53 @@ mgv6_np_apple_trees (Apple trees noise) noise_params_2d 0, 1, (100, 100, 100), 3
 [*Mapgen V7]
 
 #    Map generation attributes specific to Mapgen v7.
-#    'ridges' enables the rivers.
+#    'ridges': Rivers.
+#    'floatlands': Floating land masses in the atmosphere.
+#    'caverns': Giant caves deep underground.
 mgv7_spflags (Mapgen V7 specific flags) flags mountains,ridges,nofloatlands,caverns mountains,ridges,floatlands,caverns,nomountains,noridges,nofloatlands,nocaverns
 
 #    Y of mountain density gradient zero level. Used to shift mountains vertically.
 mgv7_mount_zero_level (Mountain zero level) int 0
 
+#    Lower Y limit of floatlands.
+mgv7_floatland_ymin (Floatland minimum Y) int 1024
+
+#    Upper Y limit of floatlands.
+mgv7_floatland_ymax (Floatland maximum Y) int 4096
+
+#    Y-distance over which floatlands taper from full density to nothing.
+#    Tapering starts at this distance from the Y limit.
+#    For a solid floatland layer, this controls the height of hills/mountains.
+#    Must be less than or equal to half the distance between the Y limits.
+mgv7_floatland_taper (Floatland tapering distance) int 256
+
+#    Exponent of the floatland tapering. Alters the tapering behaviour.
+#    Value = 1.0 creates a uniform, linear tapering.
+#    Values > 1.0 create a smooth tapering suitable for the default separated
+#    floatlands.
+#    Values < 1.0 (for example 0.25) create a more defined surface level with
+#    flatter lowlands, suitable for a solid floatland layer.
+mgv7_float_taper_exp (Floatland taper exponent) float 2.0
+
+#    Adjusts the density of the floatland layer.
+#    Increase value to increase density. Can be positive or negative.
+#    Value = 0.0: 50% of volume is floatland.
+#    Value = 2.0 (can be higher depending on 'mgv7_np_floatland', always test
+#    to be sure) creates a solid floatland layer.
+mgv7_floatland_density (Floatland density) float -0.9
+
+#    Surface level of optional water placed on a solid floatland layer.
+#    Water is disabled by default and will only be placed if this value is set
+#    to above 'mgv7_floatland_ymax' - 'mgv7_floatland_taper' (the start of the
+#    upper tapering).
+#    ***WARNING, POTENTIAL DANGER TO WORLDS AND SERVER PERFORMANCE***:
+#    When enabling water placement the floatlands must be configured and tested
+#    to be a solid layer by setting 'mgv7_floatland_density' to 2.0 (or other
+#    required value depending on 'mgv7_np_floatland'), to avoid
+#    server-intensive extreme water flow and to avoid vast flooding of the
+#    world surface below.
+mgv7_floatland_ywater (Floatland water level) int -31000
+
 #    Controls width of tunnels, a smaller value creates wider tunnels.
 #    Value >= 10.0 completely disables generation of tunnels and avoids the
 #    intensive noise calculations.
@@ -1682,6 +1723,12 @@ mgv7_np_mountain (Mountain noise) noise_params_3d -0.6, 1, (250, 350, 250), 5333
 #    3D noise defining structure of river canyon walls.
 mgv7_np_ridge (Ridge noise) noise_params_3d 0, 1, (100, 100, 100), 6467, 4, 0.75, 2.0
 
+#    3D noise defining structure of floatlands.
+#    If altered from the default, the noise 'scale' (0.7 by default) may need
+#    to be adjusted, as floatland tapering functions best when this noise has
+#    a value range of approximately -2.0 to 2.0.
+mgv7_np_floatland (Floatland noise) noise_params_3d 0, 0.7, (384, 96, 384), 1009, 4, 0.75, 1.618
+
 #    3D noise defining giant caverns.
 mgv7_np_cavern (Cavern noise) noise_params_3d 0, 1, (384, 128, 384), 723, 5, 0.63, 2.0
 
diff --git a/src/mapgen/mapgen_v7.cpp b/src/mapgen/mapgen_v7.cpp
index 43d5d822f..e93dc9140 100644
--- a/src/mapgen/mapgen_v7.cpp
+++ b/src/mapgen/mapgen_v7.cpp
@@ -1,7 +1,7 @@
 /*
 Minetest
-Copyright (C) 2013-2019 kwolekr, Ryan Kwolek <kwolekr@minetest.net>
-Copyright (C) 2014-2019 paramat
+Copyright (C) 2014-2020 paramat
+Copyright (C) 2013-2016 kwolekr, Ryan Kwolek <kwolekr@minetest.net>
 
 This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU Lesser General Public License as published by
@@ -56,6 +56,12 @@ MapgenV7::MapgenV7(MapgenV7Params *params, EmergeParams *emerge)
 {
 	spflags            = params->spflags;
 	mount_zero_level   = params->mount_zero_level;
+	floatland_ymin     = params->floatland_ymin;
+	floatland_ymax     = params->floatland_ymax;
+	floatland_taper    = params->floatland_taper;
+	float_taper_exp    = params->float_taper_exp;
+	floatland_density  = params->floatland_density;
+	floatland_ywater   = params->floatland_ywater;
 
 	cave_width         = params->cave_width;
 	large_cave_depth   = params->large_cave_depth;
@@ -70,6 +76,9 @@ MapgenV7::MapgenV7(MapgenV7Params *params, EmergeParams *emerge)
 	dungeon_ymin       = params->dungeon_ymin;
 	dungeon_ymax       = params->dungeon_ymax;
 
+	// Allocate floatland noise offset cache
+	this->float_offset_cache = new float[csize.Y + 2];
+
 	// 2D noise
 	noise_terrain_base =
 		new Noise(&params->np_terrain_base,    seed, csize.X, csize.Z);
@@ -100,6 +109,12 @@ MapgenV7::MapgenV7(MapgenV7Params *params, EmergeParams *emerge)
 			new Noise(&params->np_ridge,        seed, csize.X, csize.Y + 2, csize.Z);
 	}
 
+	if (spflags & MGV7_FLOATLANDS) {
+		// 3D noise, 1 up, 1 down overgeneration
+		noise_floatland =
+			new Noise(&params->np_floatland,    seed, csize.X, csize.Y + 2, csize.Z);
+	}
+
 	// 3D noise, 1 down overgeneration
 	MapgenBasic::np_cave1    = params->np_cave1;
 	MapgenBasic::np_cave2    = params->np_cave2;
@@ -126,6 +141,12 @@ MapgenV7::~MapgenV7()
 		delete noise_ridge_uwater;
 		delete noise_ridge;
 	}
+
+	if (spflags & MGV7_FLOATLANDS) {
+		delete noise_floatland;
+	}
+
+	delete []float_offset_cache;
 }
 
 
@@ -139,6 +160,7 @@ MapgenV7Params::MapgenV7Params():
 	np_ridge_uwater      (0.0,   1.0,   v3f(1000, 1000, 1000), 85039, 5, 0.6,  2.0),
 	np_mountain          (-0.6,  1.0,   v3f(250,  350,  250),  5333,  5, 0.63, 2.0),
 	np_ridge             (0.0,   1.0,   v3f(100,  100,  100),  6467,  4, 0.75, 2.0),
+	np_floatland         (0.0,   0.7,   v3f(384,  96,   384),  1009,  4, 0.75, 1.618),
 	np_cavern            (0.0,   1.0,   v3f(384,  128,  384),  723,   5, 0.63, 2.0),
 	np_cave1             (0.0,   12.0,  v3f(61,   61,   61),   52534, 3, 0.5,  2.0),
 	np_cave2             (0.0,   12.0,  v3f(67,   67,   67),   10325, 3, 0.5,  2.0),
@@ -151,6 +173,13 @@ void MapgenV7Params::readParams(const Settings *settings)
 {
 	settings->getFlagStrNoEx("mgv7_spflags", spflags, flagdesc_mapgen_v7);
 	settings->getS16NoEx("mgv7_mount_zero_level",       mount_zero_level);
+	settings->getS16NoEx("mgv7_floatland_ymin",         floatland_ymin);
+	settings->getS16NoEx("mgv7_floatland_ymax",         floatland_ymax);
+	settings->getS16NoEx("mgv7_floatland_taper",        floatland_taper);
+	settings->getFloatNoEx("mgv7_float_taper_exp",      float_taper_exp);
+	settings->getFloatNoEx("mgv7_floatland_density",    floatland_density);
+	settings->getS16NoEx("mgv7_floatland_ywater",       floatland_ywater);
+
 	settings->getFloatNoEx("mgv7_cave_width",           cave_width);
 	settings->getS16NoEx("mgv7_large_cave_depth",       large_cave_depth);
 	settings->getU16NoEx("mgv7_small_cave_num_min",     small_cave_num_min);
@@ -173,6 +202,7 @@ void MapgenV7Params::readParams(const Settings *settings)
 	settings->getNoiseParams("mgv7_np_ridge_uwater",    np_ridge_uwater);
 	settings->getNoiseParams("mgv7_np_mountain",        np_mountain);
 	settings->getNoiseParams("mgv7_np_ridge",           np_ridge);
+	settings->getNoiseParams("mgv7_np_floatland",       np_floatland);
 	settings->getNoiseParams("mgv7_np_cavern",          np_cavern);
 	settings->getNoiseParams("mgv7_np_cave1",           np_cave1);
 	settings->getNoiseParams("mgv7_np_cave2",           np_cave2);
@@ -184,6 +214,13 @@ void MapgenV7Params::writeParams(Settings *settings) const
 {
 	settings->setFlagStr("mgv7_spflags", spflags, flagdesc_mapgen_v7);
 	settings->setS16("mgv7_mount_zero_level",           mount_zero_level);
+	settings->setS16("mgv7_floatland_ymin",             floatland_ymin);
+	settings->setS16("mgv7_floatland_ymax",             floatland_ymax);
+	settings->setS16("mgv7_floatland_taper",            floatland_taper);
+	settings->setFloat("mgv7_float_taper_exp",          float_taper_exp);
+	settings->setFloat("mgv7_floatland_density",        floatland_density);
+	settings->setS16("mgv7_floatland_ywater",           floatland_ywater);
+
 	settings->setFloat("mgv7_cave_width",               cave_width);
 	settings->setS16("mgv7_large_cave_depth",           large_cave_depth);
 	settings->setU16("mgv7_small_cave_num_min",         small_cave_num_min);
@@ -206,6 +243,7 @@ void MapgenV7Params::writeParams(Settings *settings) const
 	settings->setNoiseParams("mgv7_np_ridge_uwater",    np_ridge_uwater);
 	settings->setNoiseParams("mgv7_np_mountain",        np_mountain);
 	settings->setNoiseParams("mgv7_np_ridge",           np_ridge);
+	settings->setNoiseParams("mgv7_np_floatland",       np_floatland);
 	settings->setNoiseParams("mgv7_np_cavern",          np_cavern);
 	settings->setNoiseParams("mgv7_np_cave1",           np_cave1);
 	settings->setNoiseParams("mgv7_np_cave2",           np_cave2);
@@ -357,8 +395,9 @@ void MapgenV7::makeChunk(BlockMakeData *data)
 	updateLiquid(&data->transforming_liquid, full_node_min, full_node_max);
 
 	// Calculate lighting
-	// TODO disable in and just below floatlands
-	bool propagate_shadow = true;
+	// Limit floatland shadows
+	bool propagate_shadow = !((spflags & MGV7_FLOATLANDS) &&
+		node_max.Y >= floatland_ymin - csize.Y * 2 && node_min.Y <= floatland_ymax);
 
 	if (flags & MG_LIGHT)
 		calcLighting(node_min - v3s16(0, 1, 0), node_max + v3s16(0, 1, 0),
@@ -427,6 +466,12 @@ bool MapgenV7::getMountainTerrainFromMap(int idx_xyz, int idx_xz, s16 y)
 }
 
 
+bool MapgenV7::getFloatlandTerrainFromMap(int idx_xyz, float float_offset)
+{
+	return noise_floatland->result[idx_xyz] + floatland_density - float_offset >= 0.0f;
+}
+
+
 int MapgenV7::generateTerrain()
 {
 	MapNode n_air(CONTENT_AIR);
@@ -446,6 +491,35 @@ int MapgenV7::generateTerrain()
 		noise_mountain->perlinMap3D(node_min.X, node_min.Y - 1, node_min.Z);
 	}
 
+	//// Floatlands
+	// 'Generate floatlands in this mapchunk' bool for
+	// simplification of condition checks in y-loop.
+	bool gen_floatlands = false;
+	u8 cache_index = 0;
+	// Y values where floatland tapering starts
+	s16 float_taper_ymax = floatland_ymax - floatland_taper;
+	s16 float_taper_ymin = floatland_ymin + floatland_taper;
+
+	if ((spflags & MGV7_FLOATLANDS) &&
+			node_max.Y >= floatland_ymin && node_min.Y <= floatland_ymax) {
+		gen_floatlands = true;
+		// Calculate noise for floatland generation
+		noise_floatland->perlinMap3D(node_min.X, node_min.Y - 1, node_min.Z);
+
+		// Cache floatland noise offset values, for floatland tapering
+		for (s16 y = node_min.Y - 1; y <= node_max.Y + 1; y++, cache_index++) {
+			float float_offset = 0.0f;
+			if (y > float_taper_ymax) {
+				float_offset = std::pow((y - float_taper_ymax) / (float)floatland_taper,
+					float_taper_exp) * 4.0f;
+			} else if (y < float_taper_ymin) {
+				float_offset = std::pow((float_taper_ymin - y) / (float)floatland_taper,
+					float_taper_exp) * 4.0f;
+			}
+			float_offset_cache[cache_index] = float_offset;
+		}
+	}
+
 	//// Place nodes
 	const v3s16 &em = vm->m_area.getExtent();
 	s16 stone_surface_max_y = -MAX_MAP_GENERATION_LIMIT;
@@ -457,13 +531,15 @@ int MapgenV7::generateTerrain()
 		if (surface_y > stone_surface_max_y)
 			stone_surface_max_y = surface_y;
 
+		cache_index = 0;
 		u32 vi = vm->m_area.index(x, node_min.Y - 1, z);
 		u32 index3d = (z - node_min.Z) * zstride_1u1d + (x - node_min.X);
 
 		for (s16 y = node_min.Y - 1; y <= node_max.Y + 1;
 				y++,
 				index3d += ystride,
-				VoxelArea::add_y(em, vi, 1)) {
+				VoxelArea::add_y(em, vi, 1),
+				cache_index++) {
 			if (vm->m_data[vi].getContent() != CONTENT_IGNORE)
 				continue;
 
@@ -474,10 +550,18 @@ int MapgenV7::generateTerrain()
 				vm->m_data[vi] = n_stone; // Mountain terrain
 				if (y > stone_surface_max_y)
 					stone_surface_max_y = y;
-			} else if (y <= water_level) {
+			} else if (gen_floatlands &&
+					getFloatlandTerrainFromMap(index3d,
+					float_offset_cache[cache_index])) {
+				vm->m_data[vi] = n_stone; // Floatland terrain
+				if (y > stone_surface_max_y)
+					stone_surface_max_y = y;
+			} else if (y <= water_level) { // Surface water
 				vm->m_data[vi] = n_water;
+			} else if (gen_floatlands && y >= float_taper_ymax && y <= floatland_ywater) {
+				vm->m_data[vi] = n_water; // Water for solid floatland layer only
 			} else {
-				vm->m_data[vi] = n_air;
+				vm->m_data[vi] = n_air; // Air
 			}
 		}
 	}
@@ -488,8 +572,8 @@ int MapgenV7::generateTerrain()
 
 void MapgenV7::generateRidgeTerrain()
 {
-	// TODO disable river canyons in floatlands
-	if (node_max.Y < water_level - 16)
+	if (node_max.Y < water_level - 16 ||
+			(node_max.Y >= floatland_ymin && node_min.Y <= floatland_ymax))
 		return;
 
 	noise_ridge->perlinMap3D(node_min.X, node_min.Y - 1, node_min.Z);
diff --git a/src/mapgen/mapgen_v7.h b/src/mapgen/mapgen_v7.h
index eeae3a956..4020cd935 100644
--- a/src/mapgen/mapgen_v7.h
+++ b/src/mapgen/mapgen_v7.h
@@ -1,7 +1,7 @@
 /*
 Minetest
-Copyright (C) 2013-2018 kwolekr, Ryan Kwolek <kwolekr@minetest.net>
-Copyright (C) 2014-2018 paramat
+Copyright (C) 2014-2020 paramat
+Copyright (C) 2013-2016 kwolekr, Ryan Kwolek <kwolekr@minetest.net>
 
 This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU Lesser General Public License as published by
@@ -36,6 +36,12 @@ extern FlagDesc flagdesc_mapgen_v7[];
 
 struct MapgenV7Params : public MapgenParams {
 	s16 mount_zero_level = 0;
+	s16 floatland_ymin = 1024;
+	s16 floatland_ymax = 4096;
+	s16 floatland_taper = 256;
+	float float_taper_exp = 2.0f;
+	float floatland_density = -0.6f;
+	s16 floatland_ywater = -31000;
 
 	float cave_width = 0.09f;
 	s16 large_cave_depth = -33;
@@ -59,6 +65,7 @@ struct MapgenV7Params : public MapgenParams {
 	NoiseParams np_ridge_uwater;
 	NoiseParams np_mountain;
 	NoiseParams np_ridge;
+	NoiseParams np_floatland;
 	NoiseParams np_cavern;
 	NoiseParams np_cave1;
 	NoiseParams np_cave2;
@@ -87,12 +94,21 @@ public:
 	float baseTerrainLevelFromMap(int index);
 	bool getMountainTerrainAtPoint(s16 x, s16 y, s16 z);
 	bool getMountainTerrainFromMap(int idx_xyz, int idx_xz, s16 y);
+	bool getFloatlandTerrainFromMap(int idx_xyz, float float_offset);
 
 	int generateTerrain();
 	void generateRidgeTerrain();
 
 private:
 	s16 mount_zero_level;
+	s16 floatland_ymin;
+	s16 floatland_ymax;
+	s16 floatland_taper;
+	float float_taper_exp;
+	float floatland_density;
+	s16 floatland_ywater;
+
+	float *float_offset_cache = nullptr;
 
 	Noise *noise_terrain_base;
 	Noise *noise_terrain_alt;
@@ -102,4 +118,5 @@ private:
 	Noise *noise_ridge_uwater;
 	Noise *noise_mountain;
 	Noise *noise_ridge;
+	Noise *noise_floatland;
 };