# tgp.cpp File Reference

OTTD Perlin Noise Landscape Generator, aka TerraGenesis Perlin. More...

`#include "stdafx.h"`
`#include <math.h>`
`#include "openttd.h"`
`#include "clear_map.h"`
`#include "variables.h"`
`#include "void_map.h"`
`#include "tgp.h"`
`#include "console.h"`
`#include "genworld.h"`
`#include "core/alloc_func.hpp"`
`#include "core/random_func.hpp"`
`#include "settings_type.h"`
`#include "table/strings.h"`

Go to the source code of this file.

## Data Structures

struct | HeightMap
| Height map - allocated array of heights (MapSizeX() + 1) x (MapSizeY() + 1). More...

## Defines

#define | M_PI_2 1.57079632679489661923
#define | M_PI 3.14159265358979323846
#define | HeightMapXY(x, y) _height_map.h[(x) + (y) * _height_map.dim_x]
| Height map accessors.
#define | I2H(i) ((i) << height_decimal_bits)
| Conversion: int to height_t.
#define | H2I(i) ((i) >> height_decimal_bits)
| Conversion: height_t to int.
#define | I2A(i) ((i) << amplitude_decimal_bits)
| Conversion: int to amplitude_t.
#define | A2I(i) ((i) >> amplitude_decimal_bits)
| Conversion: amplitude_t to int.
#define | A2H(a) ((a) >> (amplitude_decimal_bits - height_decimal_bits))
| Conversion: amplitude_t to height_t.
#define | FOR_ALL_TILES_IN_HEIGHT(h) for (h = _height_map.h; h < &_height_map.h[_height_map.total_size]; h++)
| Walk through all items of _height_map.h.

## Typedefs

typedef int16 | height_t
| Fixed point type for heights.
typedef int | amplitude_t
| Fixed point array for amplitudes (and percent values).

## Functions

static bool | IsValidXY (uint x, uint y)
| Check if a X/Y set are within the map.
static bool | AllocHeightMap ()
| Allocate array of (MapSizeX()+1)*(MapSizeY()+1) heights and init the _height_map structure members.
static void | FreeHeightMap ()
| Free height map.
static height_t | RandomHeight (amplitude_t rMax)
| RandomHeight() generator.
static bool | ApplyNoise (uint log_frequency, amplitude_t amplitude)
| One interpolation and noise round.
static void | HeightMapGenerate ()
| Base Perlin noise generator - fills height map with raw Perlin noise.
static void | HeightMapGetMinMaxAvg (height_t *min_ptr, height_t *max_ptr, height_t *avg_ptr)
| Returns min, max and average height from height map.
static int * | HeightMapMakeHistogram (height_t h_min, height_t h_max, int *hist_buf)
| Dill histogram and return pointer to its base point - to the count of zero heights.
static void | HeightMapSineTransform (height_t h_min, height_t h_max)
| Applies sine wave redistribution onto height map.
static void | HeightMapAdjustWaterLevel (amplitude_t water_percent, height_t h_max_new)
| Adjusts heights in height map to contain required amount of water tiles.
static double | perlin_coast_noise_2D (const double x, const double y, const double p, const int prime)
| This is a similar function to the main perlin noise calculation, but uses the value p passed as a parameter rather than selected from the predefined sequences.
static void | HeightMapCoastLines ()
| This routine sculpts in from the edge a random amount, again a Perlin sequence, to avoid the rigid flat-edge slopes that were present before.
static void | HeightMapSmoothCoastInDirection (int org_x, int org_y, int dir_x, int dir_y)
| Start at given point, move in given direction, find and Smooth coast in that direction.
static void | HeightMapSmoothCoasts ()
| Smooth coasts by modulating height of tiles close to map edges with cosine of distance from edge.
static void | HeightMapSmoothSlopes (height_t dh_max)
| This routine provides the essential cleanup necessary before OTTD can display the terrain.
static void | HeightMapNormalize ()

Height map terraform post processing:

- water level adjusting
- coast Smoothing
- slope Smoothing
- height histogram redistribution by sine wave transform.

static int | perlin_landXY (uint x, uint y)
static double | int_noise (const long x, const long y, const int prime)
| The Perlin Noise calculation using large primes The initial number is adjusted by two values; the generation_seed, and the passed parameter; prime.
static double | smoothed_noise (const int x, const int y, const int prime)
| Hj.
static double | linear_interpolate (const double a, const double b, const double x)
| This routine determines the interpolated value between a and b.
static double | interpolated_noise (const double x, const double y, const int prime)
| This routine returns the smoothed interpolated noise for an x and y, using the values from the surrounding positions.
static void | TgenSetTileHeight (TileIndex tile, int height)
| A small helper function.
void | GenerateTerrainPerlin ()
| The main new land generator using Perlin noise.

## Variables

static const int | height_decimal_bits = 4
static const height_t | _invalid_height = -32768
static const int | amplitude_decimal_bits = 10
static HeightMap | _height_map = {NULL, 0, 0, 0, 0}
| Global height map instance.
static const amplitude_t | _amplitudes_by_smoothness_and_frequency [4][12]

Noise amplitudes (multiplied by 1024)

- indexed by "smoothness setting" and log2(frequency).

static const amplitude_t | _water_percent [4] = {20, 80, 250, 400}
| Desired water percentage (100% == 1024) - indexed by _opt.diff.quantity_sea_lakes.
static const int8 | _max_height [4]
| Desired maximum height - indexed by _opt.diff.terrain_type.
static const double | _perlin_p_values [][7]

## Detailed Description

OTTD Perlin Noise Landscape Generator, aka TerraGenesis Perlin.

Definition in file tgp.cpp.

## Function Documentation

void GenerateTerrainPerlin | ( |  | ) |

The main new land generator using Perlin noise.

Desert landscape is handled different to all others to give a desert valley between two high mountains. Clearly if a low height terrain (flat/very flat) is chosen, then the tropic areas wont be high enough, and there will be very little tropic on the map. Thus Tropic works best on Hilly or Mountainous.

Definition at line 801 of file tgp.cpp.

References AllocHeightMap(), FreeHeightMap(), GenerateWorldSetAbortCallback(), GWP_LANDSCAPE, H2I, HeightMapGenerate(), HeightMapNormalize(), HeightMapXY, IncreaseGeneratingWorldProgress(), MakeVoid(), HeightMap::size_x, HeightMap::size_y, TgenSetTileHeight(), and TileXY().

static void HeightMapCoastLines | ( |  | ) | `[static]`

This routine sculpts in from the edge a random amount, again a Perlin sequence, to avoid the rigid flat-edge slopes that were present before.

The Perlin noise map doesnt know where we are going to slice across, and so we often cut straight through high terrain. the smoothing routine makes it legal, gradually increasing up from the edge to the original terrain height. By cutting parts of this away, it gives a far more irregular edge to the map-edge. Sometimes it works beautifully with the existing sea & lakes, and creates a very realistic coastline. Other times the variation is less, and the map-edge shows its cliff-like roots.

This routine may be extended to randomly sculpt the height of the terrain near the edge. This will have the coast edge at low level (1-3), rising in smoothed steps inland to about 15 tiles in. This should make it look as though the map has been built for the map size, rather than a slice through a larger map.

Please note that all the small numbers; 53, 101, 167, etc. are small primes to help give the perlin noise a bit more of a random feel.

Definition at line 532 of file tgp.cpp.

References abs(), HeightMapXY, max(), min(), perlin_coast_noise_2D(), HeightMap::size_x, and HeightMap::size_y.

Referenced by HeightMapNormalize().

static void HeightMapSmoothSlopes | ( | height_t | dh_max | ) | `[static]`

This routine provides the essential cleanup necessary before OTTD can display the terrain.

When generated, the terrain heights can jump more than one level between tiles. This routine smooths out those differences so that the most it can change is one level. When OTTD can support cliffs, this routine may not be necessary.

Definition at line 640 of file tgp.cpp.

References HeightMapXY, min(), HeightMap::size_x, and HeightMap::size_y.

Referenced by HeightMapNormalize().

static double int_noise | ( | const long | x,
|  | const long | y,
|  | const int | prime |
| ) |  |  | `[static]`

The Perlin Noise calculation using large primes The initial number is adjusted by two values; the generation_seed, and the passed parameter; prime.

prime is used to allow the perlin noise generator to create useful random numbers from slightly different series.

Definition at line 701 of file tgp.cpp.

Referenced by smoothed_noise().

static bool IsValidXY | ( | uint | x,
|  | uint | y |
| ) |  |  | `[inline, static]`

Check if a X/Y set are within the map.

Parameters:

  | x | coordinate x
  | y | coordinate y

Returns:
  true if within the map

Definition at line 230 of file tgp.cpp.

References HeightMap::size_x, and HeightMap::size_y.

Referenced by HeightMapSmoothCoastInDirection().

static double perlin_coast_noise_2D | ( | const double | x,
|  | const double | y,
|  | const double | p,
|  | const int | prime |
| ) |  |  | `[static]`

This is a similar function to the main perlin noise calculation, but uses the value p passed as a parameter rather than selected from the predefined sequences.

as you can guess by its title, i use this to create the indented coastline, which is just another perlin sequence.

Definition at line 771 of file tgp.cpp.

References interpolated_noise().

Referenced by HeightMapCoastLines().

static double smoothed_noise | ( | const int | x,
|  | const int | y,
|  | const int | prime |
| ) |  |  | `[static]`

Hj.

Malthaner's routine included 2 different noise smoothing methods. We now use the "raw" int_noise one. However, it may be useful to move to the other routine in future. So it is included too.

Definition at line 718 of file tgp.cpp.

References int_noise().

Referenced by interpolated_noise().

## Variable Documentation

const amplitude_t _amplitudes_by_smoothness_and_frequency[4][12]`[static]`

Initial value:

     {

      {1000,  350,  123,   43,   15,    1,     1,    0,    0,    0,    0,    0},

      {1000, 1000,  403,  200,   64,    8,     1,    0,    0,    0,    0,    0},

      {1000, 1200,  800,  500,  200,   16,     4,    0,    0,    0,    0,    0},

      {1500, 1000, 1200, 1000,  500,   32,    20,    0,    0,    0,    0,    0},
    }

Noise amplitudes (multiplied by 1024)

- indexed by "smoothness setting" and log2(frequency).

Definition at line 203 of file tgp.cpp.

Referenced by HeightMapGenerate().

const int8 _max_height[4]`[static]`

Initial value:

     {
      6,
      9,
      12,
      15
    }

Desired maximum height - indexed by _opt.diff.terrain_type.

Definition at line 218 of file tgp.cpp.

Referenced by HeightMapNormalize().

const double _perlin_p_values[][7]`[static]`

Initial value:

     {
      { 0.35, 0.35, 0.35, 0.35, 0.35, 0.25, 0.539 },
      { 0.45, 0.55, 0.45, 0.45, 0.35, 0.25, 0.89  },
      { 0.85, 0.80, 0.70, 0.45, 0.45, 0.35, 1.825 },
      { 0.95, 0.85, 0.80, 0.55, 0.55, 0.45, 2.245 }
    }

Definition at line 687 of file tgp.cpp.