src/tgp.cpp

   1 /*
   2  * This file is part of OpenTTD.
   3  * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
   4  * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
   5  * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
   6  */
   7
   8 /** @file tgp.cpp OTTD Perlin Noise Landscape Generator, aka TerraGenesis Perlin */
   9
  10 #include "stdafx.h"
  11 #include <math.h>
  12 #include "clear_map.h"
  13 #include "void_map.h"
  14 #include "genworld.h"
  15 #include "core/random_func.hpp"
  16 #include "landscape_type.h"
  17
  18 #include "safeguards.h"
  19
  20 /*
  21  *
  22  * Quickie guide to Perlin Noise
  23  * Perlin noise is a predictable pseudo random number sequence. By generating
  24  * it in 2 dimensions, it becomes a useful random map that, for a given seed
  25  * and starting X & Y, is entirely predictable. On the face of it, that may not
  26  * be useful. However, it means that if you want to replay a map in a different
  27  * terrain, or just vary the sea level, you just re-run the generator with the
  28  * same seed. The seed is an int32, and is randomised on each run of New Game.
  29  * The Scenario Generator does not randomise the value, so that you can
  30  * experiment with one terrain until you are happy, or click "Random" for a new
  31  * random seed.
  32  *
  33  * Perlin Noise is a series of "octaves" of random noise added together. By
  34  * reducing the amplitude of the noise with each octave, the first octave of
  35  * noise defines the main terrain sweep, the next the ripples on that, and the
  36  * next the ripples on that. I use 6 octaves, with the amplitude controlled by
  37  * a power ratio, usually known as a persistence or p value. This I vary by the
  38  * smoothness selection, as can be seen in the table below. The closer to 1,
  39  * the more of that octave is added. Each octave is however raised to the power
  40  * of its position in the list, so the last entry in the "smooth" row, 0.35, is
  41  * raised to the power of 6, so can only add 0.001838...  of the amplitude to
  42  * the running total.
  43  *
  44  * In other words; the first p value sets the general shape of the terrain, the
  45  * second sets the major variations to that, ... until finally the smallest
  46  * bumps are added.
  47  *
  48  * Usefully, this routine is totally scalable; so when 32bpp comes along, the
  49  * terrain can be as bumpy as you like! It is also infinitely expandable; a
  50  * single random seed terrain continues in X & Y as far as you care to
  51  * calculate. In theory, we could use just one seed value, but randomly select
  52  * where in the Perlin XY space we use for the terrain. Personally I prefer
  53  * using a simple (0, 0) to (X, Y), with a varying seed.
  54  *
  55  *
  56  * Other things i have had to do: mountainous wasn't mountainous enough, and
  57  * since we only have 0..15 heights available, I add a second generated map
  58  * (with a modified seed), onto the original. This generally raises the
  59  * terrain, which then needs scaling back down. Overall effect is a general
  60  * uplift.
  61  *
  62  * However, the values on the top of mountains are then almost guaranteed to go
  63  * too high, so large flat plateaus appeared at height 15. To counter this, I
  64  * scale all heights above 12 to proportion up to 15. It still makes the
  65  * mountains have flattish tops, rather than craggy peaks, but at least they
  66  * aren't smooth as glass.
  67  *
  68  *
  69  * For a full discussion of Perlin Noise, please visit:
  70  * http://freespace.virgin.net/hugo.elias/models/m_perlin.htm
  71  *
  72  *
  73  * Evolution II
  74  *
  75  * The algorithm as described in the above link suggests to compute each tile height
  76  * as composition of several noise waves. Some of them are computed directly by
  77  * noise(x, y) function, some are calculated using linear approximation. Our
  78  * first implementation of perlin_noise_2D() used 4 noise(x, y) calls plus
  79  * 3 linear interpolations. It was called 6 times for each tile. This was a bit
  80  * CPU expensive.
  81  *
  82  * The following implementation uses optimized algorithm that should produce
  83  * the same quality result with much less computations, but more memory accesses.
  84  * The overall speedup should be 300% to 800% depending on CPU and memory speed.
  85  *
  86  * I will try to explain it on the example below:
  87  *
  88  * Have a map of 4 x 4 tiles, our simplified noise generator produces only two
  89  * values -1 and +1, use 3 octaves with wave length 1, 2 and 4, with amplitudes
  90  * 3, 2, 1. Original algorithm produces:
  91  *
  92  * h00 = lerp(lerp(-3, 3, 0/4), lerp(3, -3, 0/4), 0/4) + lerp(lerp(-2,  2, 0/2), lerp( 2, -2, 0/2), 0/2) + -1 = lerp(-3.0,  3.0, 0/4) + lerp(-2,  2, 0/2) + -1 = -3.0  + -2 + -1 = -6.0
  93  * h01 = lerp(lerp(-3, 3, 1/4), lerp(3, -3, 1/4), 0/4) + lerp(lerp(-2,  2, 1/2), lerp( 2, -2, 1/2), 0/2) +  1 = lerp(-1.5,  1.5, 0/4) + lerp( 0,  0, 0/2) +  1 = -1.5  +  0 +  1 = -0.5
  94  * h02 = lerp(lerp(-3, 3, 2/4), lerp(3, -3, 2/4), 0/4) + lerp(lerp( 2, -2, 0/2), lerp(-2,  2, 0/2), 0/2) + -1 = lerp(   0,    0, 0/4) + lerp( 2, -2, 0/2) + -1 =    0  +  2 + -1 =  1.0
  95  * h03 = lerp(lerp(-3, 3, 3/4), lerp(3, -3, 3/4), 0/4) + lerp(lerp( 2, -2, 1/2), lerp(-2,  2, 1/2), 0/2) +  1 = lerp( 1.5, -1.5, 0/4) + lerp( 0,  0, 0/2) +  1 =  1.5  +  0 +  1 =  2.5
  96  *
  97  * h10 = lerp(lerp(-3, 3, 0/4), lerp(3, -3, 0/4), 1/4) + lerp(lerp(-2,  2, 0/2), lerp( 2, -2, 0/2), 1/2) +  1 = lerp(-3.0,  3.0, 1/4) + lerp(-2,  2, 1/2) +  1 = -1.5  +  0 +  1 = -0.5
  98  * h11 = lerp(lerp(-3, 3, 1/4), lerp(3, -3, 1/4), 1/4) + lerp(lerp(-2,  2, 1/2), lerp( 2, -2, 1/2), 1/2) + -1 = lerp(-1.5,  1.5, 1/4) + lerp( 0,  0, 1/2) + -1 = -0.75 +  0 + -1 = -1.75
  99  * h12 = lerp(lerp(-3, 3, 2/4), lerp(3, -3, 2/4), 1/4) + lerp(lerp( 2, -2, 0/2), lerp(-2,  2, 0/2), 1/2) +  1 = lerp(   0,    0, 1/4) + lerp( 2, -2, 1/2) +  1 =    0  +  0 +  1 =  1.0
 100  * h13 = lerp(lerp(-3, 3, 3/4), lerp(3, -3, 3/4), 1/4) + lerp(lerp( 2, -2, 1/2), lerp(-2,  2, 1/2), 1/2) + -1 = lerp( 1.5, -1.5, 1/4) + lerp( 0,  0, 1/2) + -1 =  0.75 +  0 + -1 = -0.25
 101  *
 102  *
 103  * Optimization 1:
 104  *
 105  * 1) we need to allocate a bit more tiles: (size_x + 1) * (size_y + 1) = (5 * 5):
 106  *
 107  * 2) setup corner values using amplitude 3
 108  * {    -3.0        X          X          X          3.0   }
 109  * {     X          X          X          X          X     }
 110  * {     X          X          X          X          X     }
 111  * {     X          X          X          X          X     }
 112  * {     3.0        X          X          X         -3.0   }
 113  *
 114  * 3a) interpolate values in the middle
 115  * {    -3.0        X          0.0        X          3.0   }
 116  * {     X          X          X          X          X     }
 117  * {     0.0        X          0.0        X          0.0   }
 118  * {     X          X          X          X          X     }
 119  * {     3.0        X          0.0        X         -3.0   }
 120  *
 121  * 3b) add patches with amplitude 2 to them
 122  * {    -5.0        X          2.0        X          1.0   }
 123  * {     X          X          X          X          X     }
 124  * {     2.0        X         -2.0        X          2.0   }
 125  * {     X          X          X          X          X     }
 126  * {     1.0        X          2.0        X         -5.0   }
 127  *
 128  * 4a) interpolate values in the middle
 129  * {    -5.0       -1.5        2.0        1.5        1.0   }
 130  * {    -1.5       -0.75       0.0        0.75       1.5   }
 131  * {     2.0        0.0       -2.0        0.0        2.0   }
 132  * {     1.5        0.75       0.0       -0.75      -1.5   }
 133  * {     1.0        1.5        2.0       -1.5       -5.0   }
 134  *
 135  * 4b) add patches with amplitude 1 to them
 136  * {    -6.0       -0.5        1.0        2.5        0.0   }
 137  * {    -0.5       -1.75       1.0       -0.25       2.5   }
 138  * {     1.0        1.0       -3.0        1.0        1.0   }
 139  * {     2.5       -0.25       1.0       -1.75      -0.5   }
 140  * {     0.0        2.5        1.0       -0.5       -6.0   }
 141  *
 142  *
 143  *
 144  * Optimization 2:
 145  *
 146  * As you can see above, each noise function was called just once. Therefore
 147  * we don't need to use noise function that calculates the noise from x, y and
 148  * some prime. The same quality result we can obtain using standard Random()
 149  * function instead.
 150  *
 151  */
 152
 153 /** Fixed point type for heights */
 154 typedef int16 height_t;
 155 static const int height_decimal_bits = 4;
 156
 157 /** Fixed point array for amplitudes (and percent values) */
 158 typedef int amplitude_t;
 159 static const int amplitude_decimal_bits = 10;
 160
 161 /** Height map - allocated array of heights (MapSizeX() + 1) x (MapSizeY() + 1) */
 162 struct HeightMap
 163 {
 164         height_t *h;         //< array of heights
 165         /* Even though the sizes are always positive, there are many cases where
 166          * X and Y need to be signed integers due to subtractions. */
 167         int      dim_x;      //< height map size_x MapSizeX() + 1
 168         int      total_size; //< height map total size
 169         int      size_x;     //< MapSizeX()
 170         int      size_y;     //< MapSizeY()
 171
 172         /**
 173          * Height map accessor
 174          * @param x X position
 175          * @param y Y position
 176          * @return height as fixed point number
 177          */
 178         inline height_t &height(uint x, uint y)
 179         {
 180                 return h[x + y * dim_x];
 181         }
 182 };
 183
 184 /** Global height map instance */
 185 static HeightMap _height_map = {nullptr, 0, 0, 0, 0};
 186
 187 /** Conversion: int to height_t */
 188 #define I2H(i) ((i) << height_decimal_bits)
 189 /** Conversion: height_t to int */
 190 #define H2I(i) ((i) >> height_decimal_bits)
 191
 192 /** Conversion: int to amplitude_t */
 193 #define I2A(i) ((i) << amplitude_decimal_bits)
 194 /** Conversion: amplitude_t to int */
 195 #define A2I(i) ((i) >> amplitude_decimal_bits)
 196
 197 /** Conversion: amplitude_t to height_t */
 198 #define A2H(a) ((a) >> (amplitude_decimal_bits - height_decimal_bits))
 199
 200
 201 /** Walk through all items of _height_map.h */
 202 #define FOR_ALL_TILES_IN_HEIGHT(h) for (h = _height_map.h; h < &_height_map.h[_height_map.total_size]; h++)
 203
 204 /** Maximum number of TGP noise frequencies. */
 205 static const int MAX_TGP_FREQUENCIES = 10;
 206
 207 /** Desired water percentage (100% == 1024) - indexed by _settings_game.difficulty.quantity_sea_lakes */
 208 static const amplitude_t _water_percent[4] = {70, 170, 270, 420};
 209
 210 /**
 211  * Gets the maximum allowed height while generating a map based on
 212  * mapsize, terraintype, and the maximum height level.
 213  * @return The maximum height for the map generation.
 214  * @note Values should never be lower than 3 since the minimum snowline height is 2.
 215  */
 216 static height_t TGPGetMaxHeight()
 217 {
 218         /**
 219          * Desired maximum height - indexed by:
 220          *  - _settings_game.difficulty.terrain_type
 221          *  - min(MapLogX(), MapLogY()) - MIN_MAP_SIZE_BITS
 222          *
 223          * It is indexed by map size as well as terrain type since the map size limits the height of
 224          * a usable mountain. For example, on a 64x64 map a 24 high single peak mountain (as if you
 225          * raised land 24 times in the center of the map) will leave only a ring of about 10 tiles
 226          * around the mountain to build on. On a 4096x4096 map, it won't cover any major part of the map.
 227          */
 228         static const int max_height[5][MAX_MAP_SIZE_BITS - MIN_MAP_SIZE_BITS + 1] = {
 229                 /* 64  128  256  512 1024 2048 4096 */
 230                 {   3,   3,   3,   3,   4,   5,   7 }, ///< Very flat
 231                 {   5,   7,   8,   9,  14,  19,  31 }, ///< Flat
 232                 {   8,   9,  10,  15,  23,  37,  61 }, ///< Hilly
 233                 {  10,  11,  17,  19,  49,  63,  73 }, ///< Mountainous
 234                 {  12,  19,  25,  31,  67,  75,  87 }, ///< Alpinist
 235         };
 236
 237         int map_size_bucket = std::min(MapLogX(), MapLogY()) - MIN_MAP_SIZE_BITS;
 238         int max_height_from_table = max_height[_settings_game.difficulty.terrain_type][map_size_bucket];
 239
 240         /* Arctic needs snow to have all industries, so make sure we allow TGP to generate this high. */
 241         if (_settings_game.game_creation.landscape == LT_ARCTIC) {
 242                 max_height_from_table += _settings_newgame.game_creation.snow_line_height;
 243                 /* Make flat a bit more flat by removing "very flat" from it, to somewhat compensate for the increase we just did. */
 244                 if (_settings_game.difficulty.terrain_type > 0) {
 245                         max_height_from_table -= max_height[_settings_game.difficulty.terrain_type - 1][map_size_bucket];
 246                 }
 247         }
 248         /* Tropic needs tropical forest to have all industries, so make sure we allow TGP to generate this high.
 249          * Tropic forest always starts at 1/4th of the max height. */
 250         if (_settings_game.game_creation.landscape == LT_TROPIC) {
 251                 max_height_from_table += CeilDiv(_settings_game.construction.max_heightlevel, 4);
 252                 /* Make flat a bit more flat by removing "very flat" from it, to somewhat compensate for the increase we just did. */
 253                 if (_settings_game.difficulty.terrain_type > 0) {
 254                         max_height_from_table -= max_height[_settings_game.difficulty.terrain_type - 1][map_size_bucket];
 255                 }
 256         }
 257
 258         return I2H(std::min<uint>(max_height_from_table, _settings_game.construction.max_heightlevel));
 259 }
 260
 261 /**
 262  * Get the amplitude associated with the currently selected
 263  * smoothness and maximum height level.
 264  * @param frequency The frequency to get the amplitudes for
 265  * @return The amplitudes to apply to the map.
 266  */
 267 static amplitude_t GetAmplitude(int frequency)
 268 {
 269         /* Base noise amplitudes (multiplied by 1024) and indexed by "smoothness setting" and log2(frequency). */
 270         static const amplitude_t amplitudes[][7] = {
 271                 /* lowest frequency ...... highest (every corner) */
 272                 {16000,  5600,  1968,   688,   240,    16,    16}, ///< Very smooth
 273                 {24000, 12800,  6400,  2700,  1024,   128,    16}, ///< Smooth
 274                 {32000, 19200, 12800,  8000,  3200,   256,    64}, ///< Rough
 275                 {48000, 24000, 19200, 16000,  8000,   512,   320}, ///< Very rough
 276         };
 277         /*
 278          * Extrapolation factors for ranges before the table.
 279          * The extrapolation is needed to account for the higher map heights. They need larger
 280          * areas with a particular gradient so that we are able to create maps without too
 281          * many steep slopes up to the wanted height level. It's definitely not perfect since
 282          * it will bring larger rectangles with similar slopes which makes the rectangular
 283          * behaviour of TGP more noticeable. However, these height differentiations cannot
 284          * happen over much smaller areas; we basically double the "range" to give a similar
 285          * slope for every doubling of map height.
 286          */
 287         static const double extrapolation_factors[] = { 3.3, 2.8, 2.3, 1.8 };
 288
 289         int smoothness = _settings_game.game_creation.tgen_smoothness;
 290
 291         /* Get the table index, and return that value if possible. */
 292         int index = frequency - MAX_TGP_FREQUENCIES + lengthof(amplitudes[smoothness]);
 293         amplitude_t amplitude = amplitudes[smoothness][std::max(0, index)];
 294         if (index >= 0) return amplitude;
 295
 296         /* We need to extrapolate the amplitude. */
 297         double extrapolation_factor = extrapolation_factors[smoothness];
 298         int height_range = I2H(16);
 299         do {
 300                 amplitude = (amplitude_t)(extrapolation_factor * (double)amplitude);
 301                 height_range <<= 1;
 302                 index++;
 303         } while (index < 0);
 304
 305         return Clamp((TGPGetMaxHeight() - height_range) / height_range, 0, 1) * amplitude;
 306 }
 307
 308 /**
 309  * Check if a X/Y set are within the map.
 310  * @param x coordinate x
 311  * @param y coordinate y
 312  * @return true if within the map
 313  */
 314 static inline bool IsValidXY(int x, int y)
 315 {
 316         return x >= 0 && x < _height_map.size_x && y >= 0 && y < _height_map.size_y;
 317 }
 318
 319
 320 /**
 321  * Allocate array of (MapSizeX()+1)*(MapSizeY()+1) heights and init the _height_map structure members
 322  * @return true on success
 323  */
 324 static inline bool AllocHeightMap()
 325 {
 326         height_t *h;
 327
 328         _height_map.size_x = MapSizeX();
 329         _height_map.size_y = MapSizeY();
 330
 331         /* Allocate memory block for height map row pointers */
 332         _height_map.total_size = (_height_map.size_x + 1) * (_height_map.size_y + 1);
 333         _height_map.dim_x = _height_map.size_x + 1;
 334         _height_map.h = CallocT<height_t>(_height_map.total_size);
 335
 336         /* Iterate through height map and initialise values. */
 337         FOR_ALL_TILES_IN_HEIGHT(h) *h = 0;
 338
 339         return true;
 340 }
 341
 342 /** Free height map */
 343 static inline void FreeHeightMap()
 344 {
 345         free(_height_map.h);
 346         _height_map.h = nullptr;
 347 }
 348
 349 /**
 350  * Generates new random height in given amplitude (generated numbers will range from - amplitude to + amplitude)
 351  * @param rMax Limit of result
 352  * @return generated height
 353  */
 354 static inline height_t RandomHeight(amplitude_t rMax)
 355 {
 356         /* Spread height into range -rMax..+rMax */
 357         return A2H(RandomRange(2 * rMax + 1) - rMax);
 358 }
 359
 360 /**
 361  * Base Perlin noise generator - fills height map with raw Perlin noise.
 362  *
 363  * This runs several iterations with increasing precision; the last iteration looks at areas
 364  * of 1 by 1 tiles, the second to last at 2 by 2 tiles and the initial 2**MAX_TGP_FREQUENCIES
 365  * by 2**MAX_TGP_FREQUENCIES tiles.
 366  */
 367 static void HeightMapGenerate()
 368 {
 369         /* Trying to apply noise to uninitialized height map */
 370         assert(_height_map.h != nullptr);
 371
 372         int start = std::max(MAX_TGP_FREQUENCIES - (int)std::min(MapLogX(), MapLogY()), 0);
 373         bool first = true;
 374
 375         for (int frequency = start; frequency < MAX_TGP_FREQUENCIES; frequency++) {
 376                 const amplitude_t amplitude = GetAmplitude(frequency);
 377
 378                 /* Ignore zero amplitudes; it means our map isn't height enough for this
 379                  * amplitude, so ignore it and continue with the next set of amplitude. */
 380                 if (amplitude == 0) continue;
 381
 382                 const int step = 1 << (MAX_TGP_FREQUENCIES - frequency - 1);
 383
 384                 if (first) {
 385                         /* This is first round, we need to establish base heights with step = size_min */
 386                         for (int y = 0; y <= _height_map.size_y; y += step) {
 387                                 for (int x = 0; x <= _height_map.size_x; x += step) {
 388                                         height_t height = (amplitude > 0) ? RandomHeight(amplitude) : 0;
 389                                         _height_map.height(x, y) = height;
 390                                 }
 391                         }
 392                         first = false;
 393                         continue;
 394                 }
 395
 396                 /* It is regular iteration round.
 397                  * Interpolate height values at odd x, even y tiles */
 398                 for (int y = 0; y <= _height_map.size_y; y += 2 * step) {
 399                         for (int x = 0; x <= _height_map.size_x - 2 * step; x += 2 * step) {
 400                                 height_t h00 = _height_map.height(x + 0 * step, y);
 401                                 height_t h02 = _height_map.height(x + 2 * step, y);
 402                                 height_t h01 = (h00 + h02) / 2;
 403                                 _height_map.height(x + 1 * step, y) = h01;
 404                         }
 405                 }
 406
 407                 /* Interpolate height values at odd y tiles */
 408                 for (int y = 0; y <= _height_map.size_y - 2 * step; y += 2 * step) {
 409                         for (int x = 0; x <= _height_map.size_x; x += step) {
 410                                 height_t h00 = _height_map.height(x, y + 0 * step);
 411                                 height_t h20 = _height_map.height(x, y + 2 * step);
 412                                 height_t h10 = (h00 + h20) / 2;
 413                                 _height_map.height(x, y + 1 * step) = h10;
 414                         }
 415                 }
 416
 417                 /* Add noise for next higher frequency (smaller steps) */
 418                 for (int y = 0; y <= _height_map.size_y; y += step) {
 419                         for (int x = 0; x <= _height_map.size_x; x += step) {
 420                                 _height_map.height(x, y) += RandomHeight(amplitude);
 421                         }
 422                 }
 423         }
 424 }
 425
 426 /** Returns min, max and average height from height map */
 427 static void HeightMapGetMinMaxAvg(height_t *min_ptr, height_t *max_ptr, height_t *avg_ptr)
 428 {
 429         height_t h_min, h_max, h_avg, *h;
 430         int64 h_accu = 0;
 431         h_min = h_max = _height_map.height(0, 0);
 432
 433         /* Get h_min, h_max and accumulate heights into h_accu */
 434         FOR_ALL_TILES_IN_HEIGHT(h) {
 435                 if (*h < h_min) h_min = *h;
 436                 if (*h > h_max) h_max = *h;
 437                 h_accu += *h;
 438         }
 439
 440         /* Get average height */
 441         h_avg = (height_t)(h_accu / (_height_map.size_x * _height_map.size_y));
 442
 443         /* Return required results */
 444         if (min_ptr != nullptr) *min_ptr = h_min;
 445         if (max_ptr != nullptr) *max_ptr = h_max;
 446         if (avg_ptr != nullptr) *avg_ptr = h_avg;
 447 }
 448
 449 /** Dill histogram and return pointer to its base point - to the count of zero heights */
 450 static int *HeightMapMakeHistogram(height_t h_min, height_t h_max, int *hist_buf)
 451 {
 452         int *hist = hist_buf - h_min;
 453         height_t *h;
 454
 455         /* Count the heights and fill the histogram */
 456         FOR_ALL_TILES_IN_HEIGHT(h) {
 457                 assert(*h >= h_min);
 458                 assert(*h <= h_max);
 459                 hist[*h]++;
 460         }
 461         return hist;
 462 }
 463
 464 /** Applies sine wave redistribution onto height map */
 465 static void HeightMapSineTransform(height_t h_min, height_t h_max)
 466 {
 467         height_t *h;
 468
 469         FOR_ALL_TILES_IN_HEIGHT(h) {
 470                 double fheight;
 471
 472                 if (*h < h_min) continue;
 473
 474                 /* Transform height into 0..1 space */
 475                 fheight = (double)(*h - h_min) / (double)(h_max - h_min);
 476                 /* Apply sine transform depending on landscape type */
 477                 switch (_settings_game.game_creation.landscape) {
 478                         case LT_TOYLAND:
 479                         case LT_TEMPERATE:
 480                                 /* Move and scale 0..1 into -1..+1 */
 481                                 fheight = 2 * fheight - 1;
 482                                 /* Sine transform */
 483                                 fheight = sin(fheight * M_PI_2);
 484                                 /* Transform it back from -1..1 into 0..1 space */
 485                                 fheight = 0.5 * (fheight + 1);
 486                                 break;
 487
 488                         case LT_ARCTIC:
 489                                 {
 490                                         /* Arctic terrain needs special height distribution.
 491                                          * Redistribute heights to have more tiles at highest (75%..100%) range */
 492                                         double sine_upper_limit = 0.75;
 493                                         double linear_compression = 2;
 494                                         if (fheight >= sine_upper_limit) {
 495                                                 /* Over the limit we do linear compression up */
 496                                                 fheight = 1.0 - (1.0 - fheight) / linear_compression;
 497                                         } else {
 498                                                 double m = 1.0 - (1.0 - sine_upper_limit) / linear_compression;
 499                                                 /* Get 0..sine_upper_limit into -1..1 */
 500                                                 fheight = 2.0 * fheight / sine_upper_limit - 1.0;
 501                                                 /* Sine wave transform */
 502                                                 fheight = sin(fheight * M_PI_2);
 503                                                 /* Get -1..1 back to 0..(1 - (1 - sine_upper_limit) / linear_compression) == 0.0..m */
 504                                                 fheight = 0.5 * (fheight + 1.0) * m;
 505                                         }
 506                                 }
 507                                 break;
 508
 509                         case LT_TROPIC:
 510                                 {
 511                                         /* Desert terrain needs special height distribution.
 512                                          * Half of tiles should be at lowest (0..25%) heights */
 513                                         double sine_lower_limit = 0.5;
 514                                         double linear_compression = 2;
 515                                         if (fheight <= sine_lower_limit) {
 516                                                 /* Under the limit we do linear compression down */
 517                                                 fheight = fheight / linear_compression;
 518                                         } else {
 519                                                 double m = sine_lower_limit / linear_compression;
 520                                                 /* Get sine_lower_limit..1 into -1..1 */
 521                                                 fheight = 2.0 * ((fheight - sine_lower_limit) / (1.0 - sine_lower_limit)) - 1.0;
 522                                                 /* Sine wave transform */
 523                                                 fheight = sin(fheight * M_PI_2);
 524                                                 /* Get -1..1 back to (sine_lower_limit / linear_compression)..1.0 */
 525                                                 fheight = 0.5 * ((1.0 - m) * fheight + (1.0 + m));
 526                                         }
 527                                 }
 528                                 break;
 529
 530                         default:
 531                                 NOT_REACHED();
 532                                 break;
 533                 }
 534                 /* Transform it back into h_min..h_max space */
 535                 *h = (height_t)(fheight * (h_max - h_min) + h_min);
 536                 if (*h < 0) *h = I2H(0);
 537                 if (*h >= h_max) *h = h_max - 1;
 538         }
 539 }
 540
 541 /**
 542  * Additional map variety is provided by applying different curve maps
 543  * to different parts of the map. A randomized low resolution grid contains
 544  * which curve map to use on each part of the make. This filtered non-linearly
 545  * to smooth out transitions between curves, so each tile could have between
 546  * 100% of one map applied or 25% of four maps.
 547  *
 548  * The curve maps define different land styles, i.e. lakes, low-lands, hills
 549  * and mountain ranges, although these are dependent on the landscape style
 550  * chosen as well.
 551  *
 552  * The level parameter dictates the resolution of the grid. A low resolution
 553  * grid will result in larger continuous areas of a land style, a higher
 554  * resolution grid splits the style into smaller areas.
 555  * @param level Rough indication of the size of the grid sections to style. Small level means large grid sections.
 556  */
 557 static void HeightMapCurves(uint level)
 558 {
 559         height_t mh = TGPGetMaxHeight() - I2H(1); // height levels above sea level only
 560
 561         /** Basically scale height X to height Y. Everything in between is interpolated. */
 562         struct control_point_t {
 563                 height_t x; ///< The height to scale from.
 564                 height_t y; ///< The height to scale to.
 565         };
 566         /* Scaled curve maps; value is in height_ts. */
 567 #define F(fraction) ((height_t)(fraction * mh))
 568         const control_point_t curve_map_1[] = { { F(0.0), F(0.0) },                       { F(0.8), F(0.13) },                       { F(1.0), F(0.4)  } };
 569         const control_point_t curve_map_2[] = { { F(0.0), F(0.0) }, { F(0.53), F(0.13) }, { F(0.8), F(0.27) },                       { F(1.0), F(0.6)  } };
 570         const control_point_t curve_map_3[] = { { F(0.0), F(0.0) }, { F(0.53), F(0.27) }, { F(0.8), F(0.57) },                       { F(1.0), F(0.8)  } };
 571         const control_point_t curve_map_4[] = { { F(0.0), F(0.0) }, { F(0.4),  F(0.3)  }, { F(0.7), F(0.8)  }, { F(0.92), F(0.99) }, { F(1.0), F(0.99) } };
 572 #undef F
 573
 574         /** Helper structure to index the different curve maps. */
 575         struct control_point_list_t {
 576                 size_t length;               ///< The length of the curve map.
 577                 const control_point_t *list; ///< The actual curve map.
 578         };
 579         const control_point_list_t curve_maps[] = {
 580                 { lengthof(curve_map_1), curve_map_1 },
 581                 { lengthof(curve_map_2), curve_map_2 },
 582                 { lengthof(curve_map_3), curve_map_3 },
 583                 { lengthof(curve_map_4), curve_map_4 },
 584         };
 585
 586         height_t ht[lengthof(curve_maps)];
 587         MemSetT(ht, 0, lengthof(ht));
 588
 589         /* Set up a grid to choose curve maps based on location; attempt to get a somewhat square grid */
 590         float factor = sqrt((float)_height_map.size_x / (float)_height_map.size_y);
 591         uint sx = Clamp((int)(((1 << level) * factor) + 0.5), 1, 128);
 592         uint sy = Clamp((int)(((1 << level) / factor) + 0.5), 1, 128);
 593         byte *c = AllocaM(byte, sx * sy);
 594
 595         for (uint i = 0; i < sx * sy; i++) {
 596                 c[i] = Random() % lengthof(curve_maps);
 597         }
 598
 599         /* Apply curves */
 600         for (int x = 0; x < _height_map.size_x; x++) {
 601
 602                 /* Get our X grid positions and bi-linear ratio */
 603                 float fx = (float)(sx * x) / _height_map.size_x + 1.0f;
 604                 uint x1 = (uint)fx;
 605                 uint x2 = x1;
 606                 float xr = 2.0f * (fx - x1) - 1.0f;
 607                 xr = sin(xr * M_PI_2);
 608                 xr = sin(xr * M_PI_2);
 609                 xr = 0.5f * (xr + 1.0f);
 610                 float xri = 1.0f - xr;
 611
 612                 if (x1 > 0) {
 613                         x1--;
 614                         if (x2 >= sx) x2--;
 615                 }
 616
 617                 for (int y = 0; y < _height_map.size_y; y++) {
 618
 619                         /* Get our Y grid position and bi-linear ratio */
 620                         float fy = (float)(sy * y) / _height_map.size_y + 1.0f;
 621                         uint y1 = (uint)fy;
 622                         uint y2 = y1;
 623                         float yr = 2.0f * (fy - y1) - 1.0f;
 624                         yr = sin(yr * M_PI_2);
 625                         yr = sin(yr * M_PI_2);
 626                         yr = 0.5f * (yr + 1.0f);
 627                         float yri = 1.0f - yr;
 628
 629                         if (y1 > 0) {
 630                                 y1--;
 631                                 if (y2 >= sy) y2--;
 632                         }
 633
 634                         uint corner_a = c[x1 + sx * y1];
 635                         uint corner_b = c[x1 + sx * y2];
 636                         uint corner_c = c[x2 + sx * y1];
 637                         uint corner_d = c[x2 + sx * y2];
 638
 639                         /* Bitmask of which curve maps are chosen, so that we do not bother
 640                          * calculating a curve which won't be used. */
 641                         uint corner_bits = 0;
 642                         corner_bits |= 1 << corner_a;
 643                         corner_bits |= 1 << corner_b;
 644                         corner_bits |= 1 << corner_c;
 645                         corner_bits |= 1 << corner_d;
 646
 647                         height_t *h = &_height_map.height(x, y);
 648
 649                         /* Do not touch sea level */
 650                         if (*h < I2H(1)) continue;
 651
 652                         /* Only scale above sea level */
 653                         *h -= I2H(1);
 654
 655                         /* Apply all curve maps that are used on this tile. */
 656                         for (uint t = 0; t < lengthof(curve_maps); t++) {
 657                                 if (!HasBit(corner_bits, t)) continue;
 658
 659                                 bool found = false;
 660                                 const control_point_t *cm = curve_maps[t].list;
 661                                 for (uint i = 0; i < curve_maps[t].length - 1; i++) {
 662                                         const control_point_t &p1 = cm[i];
 663                                         const control_point_t &p2 = cm[i + 1];
 664
 665                                         if (*h >= p1.x && *h < p2.x) {
 666                                                 ht[t] = p1.y + (*h - p1.x) * (p2.y - p1.y) / (p2.x - p1.x);
 667                                                 found = true;
 668                                                 break;
 669                                         }
 670                                 }
 671                                 assert(found);
 672                         }
 673
 674                         /* Apply interpolation of curve map results. */
 675                         *h = (height_t)((ht[corner_a] * yri + ht[corner_b] * yr) * xri + (ht[corner_c] * yri + ht[corner_d] * yr) * xr);
 676
 677                         /* Readd sea level */
 678                         *h += I2H(1);
 679                 }
 680         }
 681 }
 682
 683 /** Adjusts heights in height map to contain required amount of water tiles */
 684 static void HeightMapAdjustWaterLevel(amplitude_t water_percent, height_t h_max_new)
 685 {
 686         height_t h_min, h_max, h_avg, h_water_level;
 687         int64 water_tiles, desired_water_tiles;
 688         height_t *h;
 689         int *hist;
 690
 691         HeightMapGetMinMaxAvg(&h_min, &h_max, &h_avg);
 692
 693         /* Allocate histogram buffer and clear its cells */
 694         int *hist_buf = CallocT<int>(h_max - h_min + 1);
 695         /* Fill histogram */
 696         hist = HeightMapMakeHistogram(h_min, h_max, hist_buf);
 697
 698         /* How many water tiles do we want? */
 699         desired_water_tiles = A2I(((int64)water_percent) * (int64)(_height_map.size_x * _height_map.size_y));
 700
 701         /* Raise water_level and accumulate values from histogram until we reach required number of water tiles */
 702         for (h_water_level = h_min, water_tiles = 0; h_water_level < h_max; h_water_level++) {
 703                 water_tiles += hist[h_water_level];
 704                 if (water_tiles >= desired_water_tiles) break;
 705         }
 706
 707         /* We now have the proper water level value.
 708          * Transform the height map into new (normalized) height map:
 709          *   values from range: h_min..h_water_level will become negative so it will be clamped to 0
 710          *   values from range: h_water_level..h_max are transformed into 0..h_max_new
 711          *   where h_max_new is depending on terrain type and map size.
 712          */
 713         FOR_ALL_TILES_IN_HEIGHT(h) {
 714                 /* Transform height from range h_water_level..h_max into 0..h_max_new range */
 715                 *h = (height_t)(((int)h_max_new) * (*h - h_water_level) / (h_max - h_water_level)) + I2H(1);
 716                 /* Make sure all values are in the proper range (0..h_max_new) */
 717                 if (*h < 0) *h = I2H(0);
 718                 if (*h >= h_max_new) *h = h_max_new - 1;
 719         }
 720
 721         free(hist_buf);
 722 }
 723
 724 static double perlin_coast_noise_2D(const double x, const double y, const double p, const int prime);
 725
 726 /**
 727  * This routine sculpts in from the edge a random amount, again a Perlin
 728  * sequence, to avoid the rigid flat-edge slopes that were present before. The
 729  * Perlin noise map doesn't know where we are going to slice across, and so we
 730  * often cut straight through high terrain. The smoothing routine makes it
 731  * legal, gradually increasing up from the edge to the original terrain height.
 732  * By cutting parts of this away, it gives a far more irregular edge to the
 733  * map-edge. Sometimes it works beautifully with the existing sea & lakes, and
 734  * creates a very realistic coastline. Other times the variation is less, and
 735  * the map-edge shows its cliff-like roots.
 736  *
 737  * This routine may be extended to randomly sculpt the height of the terrain
 738  * near the edge. This will have the coast edge at low level (1-3), rising in
 739  * smoothed steps inland to about 15 tiles in. This should make it look as
 740  * though the map has been built for the map size, rather than a slice through
 741  * a larger map.
 742  *
 743  * Please note that all the small numbers; 53, 101, 167, etc. are small primes
 744  * to help give the perlin noise a bit more of a random feel.
 745  */
 746 static void HeightMapCoastLines(uint8 water_borders)
 747 {
 748         int smallest_size = std::min(_settings_game.game_creation.map_x, _settings_game.game_creation.map_y);
 749         const int margin = 4;
 750         int y, x;
 751         double max_x;
 752         double max_y;
 753
 754         /* Lower to sea level */
 755         for (y = 0; y <= _height_map.size_y; y++) {
 756                 if (HasBit(water_borders, BORDER_NE)) {
 757                         /* Top right */
 758                         max_x = abs((perlin_coast_noise_2D(_height_map.size_y - y, y, 0.9, 53) + 0.25) * 5 + (perlin_coast_noise_2D(y, y, 0.35, 179) + 1) * 12);
 759                         max_x = std::max((smallest_size * smallest_size / 64) + max_x, (smallest_size * smallest_size / 64) + margin - max_x);
 760                         if (smallest_size < 8 && max_x > 5) max_x /= 1.5;
 761                         for (x = 0; x < max_x; x++) {
 762                                 _height_map.height(x, y) = 0;
 763                         }
 764                 }
 765
 766                 if (HasBit(water_borders, BORDER_SW)) {
 767                         /* Bottom left */
 768                         max_x = abs((perlin_coast_noise_2D(_height_map.size_y - y, y, 0.85, 101) + 0.3) * 6 + (perlin_coast_noise_2D(y, y, 0.45,  67) + 0.75) * 8);
 769                         max_x = std::max((smallest_size * smallest_size / 64) + max_x, (smallest_size * smallest_size / 64) + margin - max_x);
 770                         if (smallest_size < 8 && max_x > 5) max_x /= 1.5;
 771                         for (x = _height_map.size_x; x > (_height_map.size_x - 1 - max_x); x--) {
 772                                 _height_map.height(x, y) = 0;
 773                         }
 774                 }
 775         }
 776
 777         /* Lower to sea level */
 778         for (x = 0; x <= _height_map.size_x; x++) {
 779                 if (HasBit(water_borders, BORDER_NW)) {
 780                         /* Top left */
 781                         max_y = abs((perlin_coast_noise_2D(x, _height_map.size_y / 2, 0.9, 167) + 0.4) * 5 + (perlin_coast_noise_2D(x, _height_map.size_y / 3, 0.4, 211) + 0.7) * 9);
 782                         max_y = std::max((smallest_size * smallest_size / 64) + max_y, (smallest_size * smallest_size / 64) + margin - max_y);
 783                         if (smallest_size < 8 && max_y > 5) max_y /= 1.5;
 784                         for (y = 0; y < max_y; y++) {
 785                                 _height_map.height(x, y) = 0;
 786                         }
 787                 }
 788
 789                 if (HasBit(water_borders, BORDER_SE)) {
 790                         /* Bottom right */
 791                         max_y = abs((perlin_coast_noise_2D(x, _height_map.size_y / 3, 0.85, 71) + 0.25) * 6 + (perlin_coast_noise_2D(x, _height_map.size_y / 3, 0.35, 193) + 0.75) * 12);
 792                         max_y = std::max((smallest_size * smallest_size / 64) + max_y, (smallest_size * smallest_size / 64) + margin - max_y);
 793                         if (smallest_size < 8 && max_y > 5) max_y /= 1.5;
 794                         for (y = _height_map.size_y; y > (_height_map.size_y - 1 - max_y); y--) {
 795                                 _height_map.height(x, y) = 0;
 796                         }
 797                 }
 798         }
 799 }
 800
 801 /** Start at given point, move in given direction, find and Smooth coast in that direction */
 802 static void HeightMapSmoothCoastInDirection(int org_x, int org_y, int dir_x, int dir_y)
 803 {
 804         const int max_coast_dist_from_edge = 35;
 805         const int max_coast_Smooth_depth = 35;
 806
 807         int x, y;
 808         int ed; // coast distance from edge
 809         int depth;
 810
 811         height_t h_prev = I2H(1);
 812         height_t h;
 813
 814         assert(IsValidXY(org_x, org_y));
 815
 816         /* Search for the coast (first non-water tile) */
 817         for (x = org_x, y = org_y, ed = 0; IsValidXY(x, y) && ed < max_coast_dist_from_edge; x += dir_x, y += dir_y, ed++) {
 818                 /* Coast found? */
 819                 if (_height_map.height(x, y) >= I2H(1)) break;
 820
 821                 /* Coast found in the neighborhood? */
 822                 if (IsValidXY(x + dir_y, y + dir_x) && _height_map.height(x + dir_y, y + dir_x) > 0) break;
 823
 824                 /* Coast found in the neighborhood on the other side */
 825                 if (IsValidXY(x - dir_y, y - dir_x) && _height_map.height(x - dir_y, y - dir_x) > 0) break;
 826         }
 827
 828         /* Coast found or max_coast_dist_from_edge has been reached.
 829          * Soften the coast slope */
 830         for (depth = 0; IsValidXY(x, y) && depth <= max_coast_Smooth_depth; depth++, x += dir_x, y += dir_y) {
 831                 h = _height_map.height(x, y);
 832                 h = std::min<uint>(h, h_prev + (4 + depth)); // coast softening formula
 833                 _height_map.height(x, y) = h;
 834                 h_prev = h;
 835         }
 836 }
 837
 838 /** Smooth coasts by modulating height of tiles close to map edges with cosine of distance from edge */
 839 static void HeightMapSmoothCoasts(uint8 water_borders)
 840 {
 841         int x, y;
 842         /* First Smooth NW and SE coasts (y close to 0 and y close to size_y) */
 843         for (x = 0; x < _height_map.size_x; x++) {
 844                 if (HasBit(water_borders, BORDER_NW)) HeightMapSmoothCoastInDirection(x, 0, 0, 1);
 845                 if (HasBit(water_borders, BORDER_SE)) HeightMapSmoothCoastInDirection(x, _height_map.size_y - 1, 0, -1);
 846         }
 847         /* First Smooth NE and SW coasts (x close to 0 and x close to size_x) */
 848         for (y = 0; y < _height_map.size_y; y++) {
 849                 if (HasBit(water_borders, BORDER_NE)) HeightMapSmoothCoastInDirection(0, y, 1, 0);
 850                 if (HasBit(water_borders, BORDER_SW)) HeightMapSmoothCoastInDirection(_height_map.size_x - 1, y, -1, 0);
 851         }
 852 }
 853
 854 /**
 855  * This routine provides the essential cleanup necessary before OTTD can
 856  * display the terrain. When generated, the terrain heights can jump more than
 857  * one level between tiles. This routine smooths out those differences so that
 858  * the most it can change is one level. When OTTD can support cliffs, this
 859  * routine may not be necessary.
 860  */
 861 static void HeightMapSmoothSlopes(height_t dh_max)
 862 {
 863         for (int y = 0; y <= (int)_height_map.size_y; y++) {
 864                 for (int x = 0; x <= (int)_height_map.size_x; x++) {
 865                         height_t h_max = std::min(_height_map.height(x > 0 ? x - 1 : x, y), _height_map.height(x, y > 0 ? y - 1 : y)) + dh_max;
 866                         if (_height_map.height(x, y) > h_max) _height_map.height(x, y) = h_max;
 867                 }
 868         }
 869         for (int y = _height_map.size_y; y >= 0; y--) {
 870                 for (int x = _height_map.size_x; x >= 0; x--) {
 871                         height_t h_max = std::min(_height_map.height(x < _height_map.size_x ? x + 1 : x, y), _height_map.height(x, y < _height_map.size_y ? y + 1 : y)) + dh_max;
 872                         if (_height_map.height(x, y) > h_max) _height_map.height(x, y) = h_max;
 873                 }
 874         }
 875 }
 876
 877 /**
 878  * Height map terraform post processing:
 879  *  - water level adjusting
 880  *  - coast Smoothing
 881  *  - slope Smoothing
 882  *  - height histogram redistribution by sine wave transform
 883  */
 884 static void HeightMapNormalize()
 885 {
 886         int sea_level_setting = _settings_game.difficulty.quantity_sea_lakes;
 887         const amplitude_t water_percent = sea_level_setting != (int)CUSTOM_SEA_LEVEL_NUMBER_DIFFICULTY ? _water_percent[sea_level_setting] : _settings_game.game_creation.custom_sea_level * 1024 / 100;
 888         const height_t h_max_new = TGPGetMaxHeight();
 889         const height_t roughness = 7 + 3 * _settings_game.game_creation.tgen_smoothness;
 890
 891         HeightMapAdjustWaterLevel(water_percent, h_max_new);
 892
 893         byte water_borders = _settings_game.construction.freeform_edges ? _settings_game.game_creation.water_borders : 0xF;
 894         if (water_borders == BORDERS_RANDOM) water_borders = GB(Random(), 0, 4);
 895
 896         HeightMapCoastLines(water_borders);
 897         HeightMapSmoothSlopes(roughness);
 898
 899         HeightMapSmoothCoasts(water_borders);
 900         HeightMapSmoothSlopes(roughness);
 901
 902         HeightMapSineTransform(I2H(1), h_max_new);
 903
 904         if (_settings_game.game_creation.variety > 0) {
 905                 HeightMapCurves(_settings_game.game_creation.variety);
 906         }
 907
 908         HeightMapSmoothSlopes(I2H(1));
 909 }
 910
 911 /**
 912  * The Perlin Noise calculation using large primes
 913  * The initial number is adjusted by two values; the generation_seed, and the
 914  * passed parameter; prime.
 915  * prime is used to allow the perlin noise generator to create useful random
 916  * numbers from slightly different series.
 917  */
 918 static double int_noise(const long x, const long y, const int prime)
 919 {
 920         long n = x + y * prime + _settings_game.game_creation.generation_seed;
 921
 922         n = (n << 13) ^ n;
 923
 924         /* Pseudo-random number generator, using several large primes */
 925         return 1.0 - (double)((n * (n * n * 15731 + 789221) + 1376312589) & 0x7fffffff) / 1073741824.0;
 926 }
 927
 928
 929 /**
 930  * This routine determines the interpolated value between a and b
 931  */
 932 static inline double linear_interpolate(const double a, const double b, const double x)
 933 {
 934         return a + x * (b - a);
 935 }
 936
 937
 938 /**
 939  * This routine returns the smoothed interpolated noise for an x and y, using
 940  * the values from the surrounding positions.
 941  */
 942 static double interpolated_noise(const double x, const double y, const int prime)
 943 {
 944         const int integer_X = (int)x;
 945         const int integer_Y = (int)y;
 946
 947         const double fractional_X = x - (double)integer_X;
 948         const double fractional_Y = y - (double)integer_Y;
 949
 950         const double v1 = int_noise(integer_X,     integer_Y,     prime);
 951         const double v2 = int_noise(integer_X + 1, integer_Y,     prime);
 952         const double v3 = int_noise(integer_X,     integer_Y + 1, prime);
 953         const double v4 = int_noise(integer_X + 1, integer_Y + 1, prime);
 954
 955         const double i1 = linear_interpolate(v1, v2, fractional_X);
 956         const double i2 = linear_interpolate(v3, v4, fractional_X);
 957
 958         return linear_interpolate(i1, i2, fractional_Y);
 959 }
 960
 961
 962 /**
 963  * This is a similar function to the main perlin noise calculation, but uses
 964  * the value p passed as a parameter rather than selected from the predefined
 965  * sequences. as you can guess by its title, i use this to create the indented
 966  * coastline, which is just another perlin sequence.
 967  */
 968 static double perlin_coast_noise_2D(const double x, const double y, const double p, const int prime)
 969 {
 970         double total = 0.0;
 971
 972         for (int i = 0; i < 6; i++) {
 973                 const double frequency = (double)(1 << i);
 974                 const double amplitude = pow(p, (double)i);
 975
 976                 total += interpolated_noise((x * frequency) / 64.0, (y * frequency) / 64.0, prime) * amplitude;
 977         }
 978
 979         return total;
 980 }
 981
 982
 983 /** A small helper function to initialize the terrain */
 984 static void TgenSetTileHeight(TileIndex tile, int height)
 985 {
 986         SetTileHeight(tile, height);
 987
 988         /* Only clear the tiles within the map area. */
 989         if (IsInnerTile(tile)) {
 990                 MakeClear(tile, CLEAR_GRASS, 3);
 991         }
 992 }
 993
 994 /**
 995  * The main new land generator using Perlin noise. Desert landscape is handled
 996  * different to all others to give a desert valley between two high mountains.
 997  * Clearly if a low height terrain (flat/very flat) is chosen, then the tropic
 998  * areas won't be high enough, and there will be very little tropic on the map.
 999  * Thus Tropic works best on Hilly or Mountainous.
1000  */
1001 void GenerateTerrainPerlin()
1002 {
1003         if (!AllocHeightMap()) return;
1004         GenerateWorldSetAbortCallback(FreeHeightMap);
1005
1006         HeightMapGenerate();
1007
1008         IncreaseGeneratingWorldProgress(GWP_LANDSCAPE);
1009
1010         HeightMapNormalize();
1011
1012         IncreaseGeneratingWorldProgress(GWP_LANDSCAPE);
1013
1014         /* First make sure the tiles at the north border are void tiles if needed. */
1015         if (_settings_game.construction.freeform_edges) {
1016                 for (uint x = 0; x < MapSizeX(); x++) MakeVoid(TileXY(x, 0));
1017                 for (uint y = 0; y < MapSizeY(); y++) MakeVoid(TileXY(0, y));
1018         }
1019
1020         int max_height = H2I(TGPGetMaxHeight());
1021
1022         /* Transfer height map into OTTD map */
1023         for (int y = 0; y < _height_map.size_y; y++) {
1024                 for (int x = 0; x < _height_map.size_x; x++) {
1025                         TgenSetTileHeight(TileXY(x, y), Clamp(H2I(_height_map.height(x, y)), 0, max_height));
1026                 }
1027         }
1028
1029         IncreaseGeneratingWorldProgress(GWP_LANDSCAPE);
1030
1031         FreeHeightMap();
1032         GenerateWorldSetAbortCallback(nullptr);
1033 }