Change: Use noise map to place desert and tropic zones.

Zones are no longer tied to terrain height.

Author: PeterN

src/landscape.cpp

@@ -971,18 +971,21 @@ static void GenerateTerrain(int type, uint flag)
 
 #include "table/genland.h"
 
-static void CreateDesertOrRainForest(uint desert_tropic_line)
+static void CreateDesertOrRainForest()
 {
 	uint update_freq = Map::Size() / 4;
+	int desert_tropic_line = _settings_game.game_creation.desert_coverage * 2 - 100;
 
 	for (const auto tile : Map::Iterate()) {
 		if ((tile % update_freq) == 0) IncreaseGeneratingWorldProgress(GWP_LANDSCAPE);
 
 		if (!IsValidTile(tile)) continue;
+		if (IsTileType(tile, MP_WATER)) continue;
+		if (PerlinNoise2D(TileX(tile), TileY(tile), 0.35, 37) * 100 > desert_tropic_line) continue;
 
-		auto allows_desert = [tile, desert_tropic_line](auto &offset) {
+		auto allows_desert = [tile](const auto &offset) {
 			TileIndex t = AddTileIndexDiffCWrap(tile, offset);
-			return t == INVALID_TILE || (TileHeight(t) < desert_tropic_line && !IsTileType(t, MP_WATER));
+			return t == INVALID_TILE || !IsTileType(t, MP_WATER);
 		};
 		if (std::all_of(std::begin(_make_desert_or_rainforest_data), std::end(_make_desert_or_rainforest_data), allows_desert)) {
 			SetTropicZone(tile, TROPICZONE_DESERT);
@@ -999,8 +1002,10 @@ static void CreateDesertOrRainForest(uint desert_tropic_line)
 		if ((tile % update_freq) == 0) IncreaseGeneratingWorldProgress(GWP_LANDSCAPE);
 
 		if (!IsValidTile(tile)) continue;
+		if (GetTropicZone(tile) != TROPICZONE_NORMAL) continue;
+		if (PerlinNoise2D(TileX(tile), TileY(tile), 0.5, 179) * 100 < desert_tropic_line) continue;
 
-		auto allows_rainforest = [tile](auto &offset) {
+		auto allows_rainforest = [tile](const auto &offset) {
 			TileIndex t = AddTileIndexDiffCWrap(tile, offset);
 			return t == INVALID_TILE || !IsTileType(t, MP_CLEAR) || !IsClearGround(t, CLEAR_DESERT);
 		};
@@ -1589,16 +1594,6 @@ static void CalculateSnowLine()
 	_settings_game.game_creation.snow_line_height = std::max(CalculateCoverageLine(_settings_game.game_creation.snow_coverage, 0), 2u);
 }
 
-/**
- * Calculate the line (in height) between desert and tropic.
- * @return The height of the line between desert and tropic.
- */
-static uint8_t CalculateDesertLine()
-{
-	/* CalculateCoverageLine() runs from top to bottom, so we need to invert the coverage. */
-	return CalculateCoverageLine(100 - _settings_game.game_creation.desert_coverage, 4);
-}
-
 bool GenerateLandscape(uint8_t mode)
 {
 	/* Number of steps of landscape generation */
@@ -1688,11 +1683,9 @@ bool GenerateLandscape(uint8_t mode)
 			CalculateSnowLine();
 			break;
 
-		case LandscapeType::Tropic: {
-			uint desert_tropic_line = CalculateDesertLine();
-			CreateDesertOrRainForest(desert_tropic_line);
+		case LandscapeType::Tropic:
+			CreateDesertOrRainForest();
 			break;
-		}
 
 		default:
 			break;

src/tgp.cpp

@@ -145,6 +145,7 @@
 #include "genworld.h"
 #include "core/random_func.hpp"
 #include "landscape_type.h"
+#include "tgp.h"
 
 #include "safeguards.h"
 
@@ -701,8 +702,6 @@ static void HeightMapAdjustWaterLevel(int64_t water_percent, Height h_max_new)
 	}
 }
 
-static double perlin_coast_noise_2D(const double x, const double y, const double p, const int prime);
-
 /**
  * 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
@@ -735,7 +734,7 @@ static void HeightMapCoastLines(BorderFlags water_borders)
 	for (y = 0; y <= _height_map.size_y; y++) {
 		if (water_borders.Test(BorderFlag::NorthEast)) {
 			/* Top right */
-			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);
+			max_x = abs((PerlinNoise2D(_height_map.size_y - y, y, 0.9, 53) + 0.25) * 5 + (PerlinNoise2D(y, y, 0.35, 179) + 1) * 12);
 			max_x = std::max((smallest_size * smallest_size / 64) + max_x, (smallest_size * smallest_size / 64) + margin - max_x);
 			if (smallest_size < 8 && max_x > 5) max_x /= 1.5;
 			for (x = 0; x < max_x; x++) {
@@ -745,7 +744,7 @@ static void HeightMapCoastLines(BorderFlags water_borders)
 
 		if (water_borders.Test(BorderFlag::SouthWest)) {
 			/* Bottom left */
-			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);
+			max_x = abs((PerlinNoise2D(_height_map.size_y - y, y, 0.85, 101) + 0.3) * 6 + (PerlinNoise2D(y, y, 0.45,  67) + 0.75) * 8);
 			max_x = std::max((smallest_size * smallest_size / 64) + max_x, (smallest_size * smallest_size / 64) + margin - max_x);
 			if (smallest_size < 8 && max_x > 5) max_x /= 1.5;
 			for (x = _height_map.size_x; x > (_height_map.size_x - 1 - max_x); x--) {
@@ -758,7 +757,7 @@ static void HeightMapCoastLines(BorderFlags water_borders)
 	for (x = 0; x <= _height_map.size_x; x++) {
 		if (water_borders.Test(BorderFlag::NorthWest)) {
 			/* Top left */
-			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);
+			max_y = abs((PerlinNoise2D(x, _height_map.size_y / 2, 0.9, 167) + 0.4) * 5 + (PerlinNoise2D(x, _height_map.size_y / 3, 0.4, 211) + 0.7) * 9);
 			max_y = std::max((smallest_size * smallest_size / 64) + max_y, (smallest_size * smallest_size / 64) + margin - max_y);
 			if (smallest_size < 8 && max_y > 5) max_y /= 1.5;
 			for (y = 0; y < max_y; y++) {
@@ -768,7 +767,7 @@ static void HeightMapCoastLines(BorderFlags water_borders)
 
 		if (water_borders.Test(BorderFlag::SouthEast)) {
 			/* Bottom right */
-			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);
+			max_y = abs((PerlinNoise2D(x, _height_map.size_y / 3, 0.85, 71) + 0.25) * 6 + (PerlinNoise2D(x, _height_map.size_y / 3, 0.35, 193) + 0.75) * 12);
 			max_y = std::max((smallest_size * smallest_size / 64) + max_y, (smallest_size * smallest_size / 64) + margin - max_y);
 			if (smallest_size < 8 && max_y > 5) max_y /= 1.5;
 			for (y = _height_map.size_y; y > (_height_map.size_y - 1 - max_y); y--) {
@@ -942,7 +941,7 @@ static double interpolated_noise(const double x, const double y, const int prime
  * sequences. as you can guess by its title, i use this to create the indented
  * coastline, which is just another perlin sequence.
  */
-static double perlin_coast_noise_2D(const double x, const double y, const double p, const int prime)
+double PerlinNoise2D(const double x, const double y, const double p, const int prime)
 {
 	double total = 0.0;
 

src/tgp.h

@@ -13,4 +13,6 @@
 void GenerateTerrainPerlin();
 uint GetEstimationTGPMapHeight();
 
+double PerlinNoise2D(const double x, const double y, const double p, const int prime);
+
 #endif /* TGP_H */