landscape.cpp

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/*
 * This file is part of OpenTTD.
 * 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.
 * 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.
 * 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/>.
 */
 
#include "stdafx.h"
#include "heightmap.h"
#include "clear_map.h"
#include "spritecache.h"
#include "viewport_func.h"
#include "command_func.h"
#include "landscape.h"
#include "void_map.h"
#include "tgp.h"
#include "genworld.h"
#include "fios.h"
#include "date_func.h"
#include "water.h"
#include "effectvehicle_func.h"
#include "landscape_type.h"
#include "animated_tile_func.h"
#include "core/random_func.hpp"
#include "object_base.h"
#include "company_func.h"
#include "pathfinder/npf/aystar.h"
#include "saveload/saveload.h"
#include "framerate_type.h"
#include "landscape_cmd.h"
#include "terraform_cmd.h"
#include "station_func.h"
#include <array>
#include <list>
#include <set>
 
#include "table/strings.h"
#include "table/sprites.h"
 
#include "safeguards.h"
 
extern const TileTypeProcs
  _tile_type_clear_procs,
  _tile_type_rail_procs,
  _tile_type_road_procs,
  _tile_type_town_procs,
  _tile_type_trees_procs,
  _tile_type_station_procs,
  _tile_type_water_procs,
  _tile_type_void_procs,
  _tile_type_industry_procs,
  _tile_type_tunnelbridge_procs,
  _tile_type_object_procs;
 
const TileTypeProcs * const _tile_type_procs[16] = {
  &_tile_type_clear_procs,        
  &_tile_type_rail_procs,         
  &_tile_type_road_procs,         
  &_tile_type_town_procs,         
  &_tile_type_trees_procs,        
  &_tile_type_station_procs,      
  &_tile_type_water_procs,        
  &_tile_type_void_procs,         
  &_tile_type_industry_procs,     
  &_tile_type_tunnelbridge_procs, 
  &_tile_type_object_procs,       
};
 
extern const byte _slope_to_sprite_offset[32] = {
  0, 1, 2, 3, 4, 5, 6,  7, 8, 9, 10, 11, 12, 13, 14, 0,
  0, 0, 0, 0, 0, 0, 0, 16, 0, 0,  0, 17,  0, 15, 18, 0,
};
 
static SnowLine *_snow_line = nullptr;
 
Point InverseRemapCoords2(int x, int y, bool clamp_to_map, bool *clamped)
{
  if (clamped != nullptr) *clamped = false; // Not clamping yet.
 
  /* Initial x/y world coordinate is like if the landscape
   * was completely flat on height 0. */
  Point pt = InverseRemapCoords(x, y);
 
  const uint min_coord = _settings_game.construction.freeform_edges ? TILE_SIZE : 0;
  const uint max_x = MapMaxX() * TILE_SIZE - 1;
  const uint max_y = MapMaxY() * TILE_SIZE - 1;
 
  if (clamp_to_map) {
    /* Bring the coordinates near to a valid range. At the top we allow a number
     * of extra tiles. This is mostly due to the tiles on the north side of
     * the map possibly being drawn higher due to the extra height levels. */
    int extra_tiles = CeilDiv(_settings_game.construction.map_height_limit * TILE_HEIGHT, TILE_PIXELS);
    Point old_pt = pt;
    pt.x = Clamp(pt.x, -extra_tiles * TILE_SIZE, max_x);
    pt.y = Clamp(pt.y, -extra_tiles * TILE_SIZE, max_y);
    if (clamped != nullptr) *clamped = (pt.x != old_pt.x) || (pt.y != old_pt.y);
  }
 
  /* Now find the Z-world coordinate by fix point iteration.
   * This is a bit tricky because the tile height is non-continuous at foundations.
   * The clicked point should be approached from the back, otherwise there are regions that are not clickable.
   * (FOUNDATION_HALFTILE_LOWER on SLOPE_STEEP_S hides north halftile completely)
   * So give it a z-malus of 4 in the first iterations. */
  int z = 0;
  if (clamp_to_map) {
    for (int i = 0; i < 5; i++) z = GetSlopePixelZ(Clamp(pt.x + std::max(z, 4) - 4, min_coord, max_x), Clamp(pt.y + std::max(z, 4) - 4, min_coord, max_y)) / 2;
    for (int m = 3; m > 0; m--) z = GetSlopePixelZ(Clamp(pt.x + std::max(z, m) - m, min_coord, max_x), Clamp(pt.y + std::max(z, m) - m, min_coord, max_y)) / 2;
    for (int i = 0; i < 5; i++) z = GetSlopePixelZ(Clamp(pt.x + z,             min_coord, max_x), Clamp(pt.y + z,             min_coord, max_y)) / 2;
  } else {
    for (int i = 0; i < 5; i++) z = GetSlopePixelZOutsideMap(pt.x + std::max(z, 4) - 4, pt.y + std::max(z, 4) - 4) / 2;
    for (int m = 3; m > 0; m--) z = GetSlopePixelZOutsideMap(pt.x + std::max(z, m) - m, pt.y + std::max(z, m) - m) / 2;
    for (int i = 0; i < 5; i++) z = GetSlopePixelZOutsideMap(pt.x + z,             pt.y + z            ) / 2;
  }
 
  pt.x += z;
  pt.y += z;
  if (clamp_to_map) {
    Point old_pt = pt;
    pt.x = Clamp(pt.x, min_coord, max_x);
    pt.y = Clamp(pt.y, min_coord, max_y);
    if (clamped != nullptr) *clamped = *clamped || (pt.x != old_pt.x) || (pt.y != old_pt.y);
  }
 
  return pt;
}
 
uint ApplyFoundationToSlope(Foundation f, Slope *s)
{
  if (!IsFoundation(f)) return 0;
 
  if (IsLeveledFoundation(f)) {
    uint dz = 1 + (IsSteepSlope(*s) ? 1 : 0);
    *s = SLOPE_FLAT;
    return dz;
  }
 
  if (f != FOUNDATION_STEEP_BOTH && IsNonContinuousFoundation(f)) {
    *s = HalftileSlope(*s, GetHalftileFoundationCorner(f));
    return 0;
  }
 
  if (IsSpecialRailFoundation(f)) {
    *s = SlopeWithThreeCornersRaised(OppositeCorner(GetRailFoundationCorner(f)));
    return 0;
  }
 
  uint dz = IsSteepSlope(*s) ? 1 : 0;
  Corner highest_corner = GetHighestSlopeCorner(*s);
 
  switch (f) {
    case FOUNDATION_INCLINED_X:
      *s = (((highest_corner == CORNER_W) || (highest_corner == CORNER_S)) ? SLOPE_SW : SLOPE_NE);
      break;
 
    case FOUNDATION_INCLINED_Y:
      *s = (((highest_corner == CORNER_S) || (highest_corner == CORNER_E)) ? SLOPE_SE : SLOPE_NW);
      break;
 
    case FOUNDATION_STEEP_LOWER:
      *s = SlopeWithOneCornerRaised(highest_corner);
      break;
 
    case FOUNDATION_STEEP_BOTH:
      *s = HalftileSlope(SlopeWithOneCornerRaised(highest_corner), highest_corner);
      break;
 
    default: NOT_REACHED();
  }
  return dz;
}
 
 
uint GetPartialPixelZ(int x, int y, Slope corners)
{
  if (IsHalftileSlope(corners)) {
    switch (GetHalftileSlopeCorner(corners)) {
      case CORNER_W:
        if (x - y >= 0) return GetSlopeMaxPixelZ(corners);
        break;
 
      case CORNER_S:
        if (x - (y ^ 0xF) >= 0) return GetSlopeMaxPixelZ(corners);
        break;
 
      case CORNER_E:
        if (y - x >= 0) return GetSlopeMaxPixelZ(corners);
        break;
 
      case CORNER_N:
        if ((y ^ 0xF) - x >= 0) return GetSlopeMaxPixelZ(corners);
        break;
 
      default: NOT_REACHED();
    }
  }
 
  int z = 0;
 
  switch (RemoveHalftileSlope(corners)) {
    case SLOPE_W:
      if (x - y >= 0) {
        z = (x - y) >> 1;
      }
      break;
 
    case SLOPE_S:
      y ^= 0xF;
      if ((x - y) >= 0) {
        z = (x - y) >> 1;
      }
      break;
 
    case SLOPE_SW:
      z = (x >> 1) + 1;
      break;
 
    case SLOPE_E:
      if (y - x >= 0) {
        z = (y - x) >> 1;
      }
      break;
 
    case SLOPE_EW:
    case SLOPE_NS:
    case SLOPE_ELEVATED:
      z = 4;
      break;
 
    case SLOPE_SE:
      z = (y >> 1) + 1;
      break;
 
    case SLOPE_WSE:
      z = 8;
      y ^= 0xF;
      if (x - y < 0) {
        z += (x - y) >> 1;
      }
      break;
 
    case SLOPE_N:
      y ^= 0xF;
      if (y - x >= 0) {
        z = (y - x) >> 1;
      }
      break;
 
    case SLOPE_NW:
      z = (y ^ 0xF) >> 1;
      break;
 
    case SLOPE_NWS:
      z = 8;
      if (x - y < 0) {
        z += (x - y) >> 1;
      }
      break;
 
    case SLOPE_NE:
      z = (x ^ 0xF) >> 1;
      break;
 
    case SLOPE_ENW:
      z = 8;
      y ^= 0xF;
      if (y - x < 0) {
        z += (y - x) >> 1;
      }
      break;
 
    case SLOPE_SEN:
      z = 8;
      if (y - x < 0) {
        z += (y - x) >> 1;
      }
      break;
 
    case SLOPE_STEEP_S:
      z = 1 + ((x + y) >> 1);
      break;
 
    case SLOPE_STEEP_W:
      z = 1 + ((x + (y ^ 0xF)) >> 1);
      break;
 
    case SLOPE_STEEP_N:
      z = 1 + (((x ^ 0xF) + (y ^ 0xF)) >> 1);
      break;
 
    case SLOPE_STEEP_E:
      z = 1 + (((x ^ 0xF) + y) >> 1);
      break;
 
    default: break;
  }
 
  return z;
}
 
int GetSlopePixelZ(int x, int y)
{
  TileIndex tile = TileVirtXY(x, y);
 
  return _tile_type_procs[GetTileType(tile)]->get_slope_z_proc(tile, x, y);
}
 
int GetSlopePixelZOutsideMap(int x, int y)
{
  if (IsInsideBS(x, 0, MapSizeX() * TILE_SIZE) && IsInsideBS(y, 0, MapSizeY() * TILE_SIZE)) {
    return GetSlopePixelZ(x, y);
  } else {
    return _tile_type_procs[MP_VOID]->get_slope_z_proc(INVALID_TILE, x, y);
  }
}
 
int GetSlopeZInCorner(Slope tileh, Corner corner)
{
  assert(!IsHalftileSlope(tileh));
  return ((tileh & SlopeWithOneCornerRaised(corner)) != 0 ? 1 : 0) + (tileh == SteepSlope(corner) ? 1 : 0);
}
 
void GetSlopePixelZOnEdge(Slope tileh, DiagDirection edge, int *z1, int *z2)
{
  static const Slope corners[4][4] = {
    /*    corner     |          steep slope
     *  z1      z2   |       z1             z2        */
    {SLOPE_E, SLOPE_N, SLOPE_STEEP_E, SLOPE_STEEP_N}, // DIAGDIR_NE, z1 = E, z2 = N
    {SLOPE_S, SLOPE_E, SLOPE_STEEP_S, SLOPE_STEEP_E}, // DIAGDIR_SE, z1 = S, z2 = E
    {SLOPE_S, SLOPE_W, SLOPE_STEEP_S, SLOPE_STEEP_W}, // DIAGDIR_SW, z1 = S, z2 = W
    {SLOPE_W, SLOPE_N, SLOPE_STEEP_W, SLOPE_STEEP_N}, // DIAGDIR_NW, z1 = W, z2 = N
  };
 
  int halftile_test = (IsHalftileSlope(tileh) ? SlopeWithOneCornerRaised(GetHalftileSlopeCorner(tileh)) : 0);
  if (halftile_test == corners[edge][0]) *z2 += TILE_HEIGHT; // The slope is non-continuous in z2. z2 is on the upper side.
  if (halftile_test == corners[edge][1]) *z1 += TILE_HEIGHT; // The slope is non-continuous in z1. z1 is on the upper side.
 
  if ((tileh & corners[edge][0]) != 0) *z1 += TILE_HEIGHT; // z1 is raised
  if ((tileh & corners[edge][1]) != 0) *z2 += TILE_HEIGHT; // z2 is raised
  if (RemoveHalftileSlope(tileh) == corners[edge][2]) *z1 += TILE_HEIGHT; // z1 is highest corner of a steep slope
  if (RemoveHalftileSlope(tileh) == corners[edge][3]) *z2 += TILE_HEIGHT; // z2 is highest corner of a steep slope
}
 
Slope GetFoundationSlope(TileIndex tile, int *z)
{
  Slope tileh = GetTileSlope(tile, z);
  Foundation f = _tile_type_procs[GetTileType(tile)]->get_foundation_proc(tile, tileh);
  uint z_inc = ApplyFoundationToSlope(f, &tileh);
  if (z != nullptr) *z += z_inc;
  return tileh;
}
 
 
bool HasFoundationNW(TileIndex tile, Slope slope_here, uint z_here)
{
  int z;
 
  int z_W_here = z_here;
  int z_N_here = z_here;
  GetSlopePixelZOnEdge(slope_here, DIAGDIR_NW, &z_W_here, &z_N_here);
 
  Slope slope = GetFoundationPixelSlope(TILE_ADDXY(tile, 0, -1), &z);
  int z_W = z;
  int z_N = z;
  GetSlopePixelZOnEdge(slope, DIAGDIR_SE, &z_W, &z_N);
 
  return (z_N_here > z_N) || (z_W_here > z_W);
}
 
 
bool HasFoundationNE(TileIndex tile, Slope slope_here, uint z_here)
{
  int z;
 
  int z_E_here = z_here;
  int z_N_here = z_here;
  GetSlopePixelZOnEdge(slope_here, DIAGDIR_NE, &z_E_here, &z_N_here);
 
  Slope slope = GetFoundationPixelSlope(TILE_ADDXY(tile, -1, 0), &z);
  int z_E = z;
  int z_N = z;
  GetSlopePixelZOnEdge(slope, DIAGDIR_SW, &z_E, &z_N);
 
  return (z_N_here > z_N) || (z_E_here > z_E);
}
 
void DrawFoundation(TileInfo *ti, Foundation f)
{
  if (!IsFoundation(f)) return;
 
  /* Two part foundations must be drawn separately */
  assert(f != FOUNDATION_STEEP_BOTH);
 
  uint sprite_block = 0;
  int z;
  Slope slope = GetFoundationPixelSlope(ti->tile, &z);
 
  /* Select the needed block of foundations sprites
   * Block 0: Walls at NW and NE edge
   * Block 1: Wall  at        NE edge
   * Block 2: Wall  at NW        edge
   * Block 3: No walls at NW or NE edge
   */
  if (!HasFoundationNW(ti->tile, slope, z)) sprite_block += 1;
  if (!HasFoundationNE(ti->tile, slope, z)) sprite_block += 2;
 
  /* Use the original slope sprites if NW and NE borders should be visible */
  SpriteID leveled_base = (sprite_block == 0 ? (int)SPR_FOUNDATION_BASE : (SPR_SLOPES_VIRTUAL_BASE + sprite_block * SPR_TRKFOUND_BLOCK_SIZE));
  SpriteID inclined_base = SPR_SLOPES_VIRTUAL_BASE + SPR_SLOPES_INCLINED_OFFSET + sprite_block * SPR_TRKFOUND_BLOCK_SIZE;
  SpriteID halftile_base = SPR_HALFTILE_FOUNDATION_BASE + sprite_block * SPR_HALFTILE_BLOCK_SIZE;
 
  if (IsSteepSlope(ti->tileh)) {
    if (!IsNonContinuousFoundation(f)) {
      /* Lower part of foundation */
      AddSortableSpriteToDraw(
        leveled_base + (ti->tileh & ~SLOPE_STEEP), PAL_NONE, ti->x, ti->y, 16, 16, 7, ti->z
      );
    }
 
    Corner highest_corner = GetHighestSlopeCorner(ti->tileh);
    ti->z += ApplyPixelFoundationToSlope(f, &ti->tileh);
 
    if (IsInclinedFoundation(f)) {
      /* inclined foundation */
      byte inclined = highest_corner * 2 + (f == FOUNDATION_INCLINED_Y ? 1 : 0);
 
      AddSortableSpriteToDraw(inclined_base + inclined, PAL_NONE, ti->x, ti->y,
        f == FOUNDATION_INCLINED_X ? 16 : 1,
        f == FOUNDATION_INCLINED_Y ? 16 : 1,
        TILE_HEIGHT, ti->z
      );
      OffsetGroundSprite(31, 9);
    } else if (IsLeveledFoundation(f)) {
      AddSortableSpriteToDraw(leveled_base + SlopeWithOneCornerRaised(highest_corner), PAL_NONE, ti->x, ti->y, 16, 16, 7, ti->z - TILE_HEIGHT);
      OffsetGroundSprite(31, 1);
    } else if (f == FOUNDATION_STEEP_LOWER) {
      /* one corner raised */
      OffsetGroundSprite(31, 1);
    } else {
      /* halftile foundation */
      int x_bb = (((highest_corner == CORNER_W) || (highest_corner == CORNER_S)) ? 8 : 0);
      int y_bb = (((highest_corner == CORNER_S) || (highest_corner == CORNER_E)) ? 8 : 0);
 
      AddSortableSpriteToDraw(halftile_base + highest_corner, PAL_NONE, ti->x + x_bb, ti->y + y_bb, 8, 8, 7, ti->z + TILE_HEIGHT);
      OffsetGroundSprite(31, 9);
    }
  } else {
    if (IsLeveledFoundation(f)) {
      /* leveled foundation */
      AddSortableSpriteToDraw(leveled_base + ti->tileh, PAL_NONE, ti->x, ti->y, 16, 16, 7, ti->z);
      OffsetGroundSprite(31, 1);
    } else if (IsNonContinuousFoundation(f)) {
      /* halftile foundation */
      Corner halftile_corner = GetHalftileFoundationCorner(f);
      int x_bb = (((halftile_corner == CORNER_W) || (halftile_corner == CORNER_S)) ? 8 : 0);
      int y_bb = (((halftile_corner == CORNER_S) || (halftile_corner == CORNER_E)) ? 8 : 0);
 
      AddSortableSpriteToDraw(halftile_base + halftile_corner, PAL_NONE, ti->x + x_bb, ti->y + y_bb, 8, 8, 7, ti->z);
      OffsetGroundSprite(31, 9);
    } else if (IsSpecialRailFoundation(f)) {
      /* anti-zig-zag foundation */
      SpriteID spr;
      if (ti->tileh == SLOPE_NS || ti->tileh == SLOPE_EW) {
        /* half of leveled foundation under track corner */
        spr = leveled_base + SlopeWithThreeCornersRaised(GetRailFoundationCorner(f));
      } else {
        /* tile-slope = sloped along X/Y, foundation-slope = three corners raised */
        spr = inclined_base + 2 * GetRailFoundationCorner(f) + ((ti->tileh == SLOPE_SW || ti->tileh == SLOPE_NE) ? 1 : 0);
      }
      AddSortableSpriteToDraw(spr, PAL_NONE, ti->x, ti->y, 16, 16, 7, ti->z);
      OffsetGroundSprite(31, 9);
    } else {
      /* inclined foundation */
      byte inclined = GetHighestSlopeCorner(ti->tileh) * 2 + (f == FOUNDATION_INCLINED_Y ? 1 : 0);
 
      AddSortableSpriteToDraw(inclined_base + inclined, PAL_NONE, ti->x, ti->y,
        f == FOUNDATION_INCLINED_X ? 16 : 1,
        f == FOUNDATION_INCLINED_Y ? 16 : 1,
        TILE_HEIGHT, ti->z
      );
      OffsetGroundSprite(31, 9);
    }
    ti->z += ApplyPixelFoundationToSlope(f, &ti->tileh);
  }
}
 
void DoClearSquare(TileIndex tile)
{
  /* If the tile can have animation and we clear it, delete it from the animated tile list. */
  if (_tile_type_procs[GetTileType(tile)]->animate_tile_proc != nullptr) DeleteAnimatedTile(tile);
 
  bool remove = IsDockingTile(tile);
  MakeClear(tile, CLEAR_GRASS, _generating_world ? 3 : 0);
  MarkTileDirtyByTile(tile);
  if (remove) RemoveDockingTile(tile);
}
 
TrackStatus GetTileTrackStatus(TileIndex tile, TransportType mode, uint sub_mode, DiagDirection side)
{
  return _tile_type_procs[GetTileType(tile)]->get_tile_track_status_proc(tile, mode, sub_mode, side);
}
 
void ChangeTileOwner(TileIndex tile, Owner old_owner, Owner new_owner)
{
  _tile_type_procs[GetTileType(tile)]->change_tile_owner_proc(tile, old_owner, new_owner);
}
 
void GetTileDesc(TileIndex tile, TileDesc *td)
{
  _tile_type_procs[GetTileType(tile)]->get_tile_desc_proc(tile, td);
}
 
bool IsSnowLineSet()
{
  return _snow_line != nullptr;
}
 
void SetSnowLine(byte table[SNOW_LINE_MONTHS][SNOW_LINE_DAYS])
{
  _snow_line = CallocT<SnowLine>(1);
  _snow_line->lowest_value = 0xFF;
  memcpy(_snow_line->table, table, sizeof(_snow_line->table));
 
  for (uint i = 0; i < SNOW_LINE_MONTHS; i++) {
    for (uint j = 0; j < SNOW_LINE_DAYS; j++) {
      _snow_line->highest_value = std::max(_snow_line->highest_value, table[i][j]);
      _snow_line->lowest_value = std::min(_snow_line->lowest_value, table[i][j]);
    }
  }
}
 
byte GetSnowLine()
{
  if (_snow_line == nullptr) return _settings_game.game_creation.snow_line_height;
 
  YearMonthDay ymd;
  ConvertDateToYMD(_date, &ymd);
  return _snow_line->table[ymd.month][ymd.day];
}
 
byte HighestSnowLine()
{
  return _snow_line == nullptr ? _settings_game.game_creation.snow_line_height : _snow_line->highest_value;
}
 
byte LowestSnowLine()
{
  return _snow_line == nullptr ? _settings_game.game_creation.snow_line_height : _snow_line->lowest_value;
}
 
void ClearSnowLine()
{
  free(_snow_line);
  _snow_line = nullptr;
}
 
CommandCost CmdLandscapeClear(DoCommandFlag flags, TileIndex tile)
{
  CommandCost cost(EXPENSES_CONSTRUCTION);
  bool do_clear = false;
  /* Test for stuff which results in water when cleared. Then add the cost to also clear the water. */
  if ((flags & DC_FORCE_CLEAR_TILE) && HasTileWaterClass(tile) && IsTileOnWater(tile) && !IsWaterTile(tile) && !IsCoastTile(tile)) {
    if ((flags & DC_AUTO) && GetWaterClass(tile) == WATER_CLASS_CANAL) return_cmd_error(STR_ERROR_MUST_DEMOLISH_CANAL_FIRST);
    do_clear = true;
    cost.AddCost(GetWaterClass(tile) == WATER_CLASS_CANAL ? _price[PR_CLEAR_CANAL] : _price[PR_CLEAR_WATER]);
  }
 
  Company *c = (flags & (DC_AUTO | DC_BANKRUPT)) ? nullptr : Company::GetIfValid(_current_company);
  if (c != nullptr && (int)GB(c->clear_limit, 16, 16) < 1) {
    return_cmd_error(STR_ERROR_CLEARING_LIMIT_REACHED);
  }
 
  const ClearedObjectArea *coa = FindClearedObject(tile);
 
  /* If this tile was the first tile which caused object destruction, always
   * pass it on to the tile_type_proc. That way multiple test runs and the exec run stay consistent. */
  if (coa != nullptr && coa->first_tile != tile) {
    /* If this tile belongs to an object which was already cleared via another tile, pretend it has been
     * already removed.
     * However, we need to check stuff, which is not the same for all object tiles. (e.g. being on water or not) */
 
    /* If a object is removed, it leaves either bare land or water. */
    if ((flags & DC_NO_WATER) && HasTileWaterClass(tile) && IsTileOnWater(tile)) {
      return_cmd_error(STR_ERROR_CAN_T_BUILD_ON_WATER);
    }
  } else {
    cost.AddCost(_tile_type_procs[GetTileType(tile)]->clear_tile_proc(tile, flags));
  }
 
  if (flags & DC_EXEC) {
    if (c != nullptr) c->clear_limit -= 1 << 16;
    if (do_clear) DoClearSquare(tile);
  }
  return cost;
}
 
std::tuple<CommandCost, Money> CmdClearArea(DoCommandFlag flags, TileIndex tile, TileIndex start_tile, bool diagonal)
{
  if (start_tile >= MapSize()) return { CMD_ERROR, 0 };
 
  Money money = GetAvailableMoneyForCommand();
  CommandCost cost(EXPENSES_CONSTRUCTION);
  CommandCost last_error = CMD_ERROR;
  bool had_success = false;
 
  const Company *c = (flags & (DC_AUTO | DC_BANKRUPT)) ? nullptr : Company::GetIfValid(_current_company);
  int limit = (c == nullptr ? INT32_MAX : GB(c->clear_limit, 16, 16));
 
  TileIterator *iter = diagonal ? (TileIterator *)new DiagonalTileIterator(tile, start_tile) : new OrthogonalTileIterator(tile, start_tile);
  for (; *iter != INVALID_TILE; ++(*iter)) {
    TileIndex t = *iter;
    CommandCost ret = Command<CMD_LANDSCAPE_CLEAR>::Do(flags & ~DC_EXEC, t);
    if (ret.Failed()) {
      last_error = ret;
 
      /* We may not clear more tiles. */
      if (c != nullptr && GB(c->clear_limit, 16, 16) < 1) break;
      continue;
    }
 
    had_success = true;
    if (flags & DC_EXEC) {
      money -= ret.GetCost();
      if (ret.GetCost() > 0 && money < 0) {
        delete iter;
        return { cost, ret.GetCost() };
      }
      Command<CMD_LANDSCAPE_CLEAR>::Do(flags, t);
 
      /* draw explosion animation...
       * Disable explosions when game is paused. Looks silly and blocks the view. */
      if ((t == tile || t == start_tile) && _pause_mode == PM_UNPAUSED) {
        /* big explosion in two corners, or small explosion for single tiles */
        CreateEffectVehicleAbove(TileX(t) * TILE_SIZE + TILE_SIZE / 2, TileY(t) * TILE_SIZE + TILE_SIZE / 2, 2,
          TileX(tile) == TileX(start_tile) && TileY(tile) == TileY(start_tile) ? EV_EXPLOSION_SMALL : EV_EXPLOSION_LARGE
        );
      }
    } else {
      /* When we're at the clearing limit we better bail (unneed) testing as well. */
      if (ret.GetCost() != 0 && --limit <= 0) break;
    }
    cost.AddCost(ret);
  }
 
  delete iter;
  return { had_success ? cost : last_error, 0 };
}
 
 
TileIndex _cur_tileloop_tile;
 
void RunTileLoop()
{
  PerformanceAccumulator framerate(PFE_GL_LANDSCAPE);
 
  /* The pseudorandom sequence of tiles is generated using a Galois linear feedback
   * shift register (LFSR). This allows a deterministic pseudorandom ordering, but
   * still with minimal state and fast iteration. */
 
  /* Maximal length LFSR feedback terms, from 12-bit (for 64x64 maps) to 24-bit (for 4096x4096 maps).
   * Extracted from http://www.ece.cmu.edu/~koopman/lfsr/ */
  static const uint32 feedbacks[] = {
    0xD8F, 0x1296, 0x2496, 0x4357, 0x8679, 0x1030E, 0x206CD, 0x403FE, 0x807B8, 0x1004B2, 0x2006A8, 0x4004B2, 0x800B87
  };
  static_assert(lengthof(feedbacks) == 2 * MAX_MAP_SIZE_BITS - 2 * MIN_MAP_SIZE_BITS + 1);
  const uint32 feedback = feedbacks[MapLogX() + MapLogY() - 2 * MIN_MAP_SIZE_BITS];
 
  /* We update every tile every 256 ticks, so divide the map size by 2^8 = 256 */
  uint count = 1 << (MapLogX() + MapLogY() - 8);
 
  TileIndex tile = _cur_tileloop_tile;
  /* The LFSR cannot have a zeroed state. */
  assert(tile != 0);
 
  /* Manually update tile 0 every 256 ticks - the LFSR never iterates over it itself.  */
  if (_tick_counter % 256 == 0) {
    _tile_type_procs[GetTileType(0)]->tile_loop_proc(0);
    count--;
  }
 
  while (count--) {
    _tile_type_procs[GetTileType(tile)]->tile_loop_proc(tile);
 
    /* Get the next tile in sequence using a Galois LFSR. */
    tile = (tile >> 1) ^ (-(int32)(tile & 1) & feedback);
  }
 
  _cur_tileloop_tile = tile;
}
 
void InitializeLandscape()
{
  for (uint y = _settings_game.construction.freeform_edges ? 1 : 0; y < MapMaxY(); y++) {
    for (uint x = _settings_game.construction.freeform_edges ? 1 : 0; x < MapMaxX(); x++) {
      MakeClear(TileXY(x, y), CLEAR_GRASS, 3);
      SetTileHeight(TileXY(x, y), 0);
      SetTropicZone(TileXY(x, y), TROPICZONE_NORMAL);
      ClearBridgeMiddle(TileXY(x, y));
    }
  }
 
  for (uint x = 0; x < MapSizeX(); x++) MakeVoid(TileXY(x, MapMaxY()));
  for (uint y = 0; y < MapSizeY(); y++) MakeVoid(TileXY(MapMaxX(), y));
}
 
static const byte _genterrain_tbl_1[5] = { 10, 22, 33, 37, 4  };
static const byte _genterrain_tbl_2[5] = {  0,  0,  0,  0, 33 };
 
static void GenerateTerrain(int type, uint flag)
{
  uint32 r = Random();
 
  const Sprite *templ = GetSprite((((r >> 24) * _genterrain_tbl_1[type]) >> 8) + _genterrain_tbl_2[type] + 4845, ST_MAPGEN);
  if (templ == nullptr) usererror("Map generator sprites could not be loaded");
 
  uint x = r & MapMaxX();
  uint y = (r >> MapLogX()) & MapMaxY();
 
  uint edge_distance = 1 + (_settings_game.construction.freeform_edges ? 1 : 0);
  if (x <= edge_distance || y <= edge_distance) return;
 
  DiagDirection direction = (DiagDirection)GB(r, 22, 2);
  uint w = templ->width;
  uint h = templ->height;
 
  if (DiagDirToAxis(direction) == AXIS_Y) Swap(w, h);
 
  const byte *p = templ->data;
 
  if ((flag & 4) != 0) {
    uint xw = x * MapSizeY();
    uint yw = y * MapSizeX();
    uint bias = (MapSizeX() + MapSizeY()) * 16;
 
    switch (flag & 3) {
      default: NOT_REACHED();
      case 0:
        if (xw + yw > MapSize() - bias) return;
        break;
 
      case 1:
        if (yw < xw + bias) return;
        break;
 
      case 2:
        if (xw + yw < MapSize() + bias) return;
        break;
 
      case 3:
        if (xw < yw + bias) return;
        break;
    }
  }
 
  if (x + w >= MapMaxX()) return;
  if (y + h >= MapMaxY()) return;
 
  TileIndex tile = TileXY(x, y);
 
  switch (direction) {
    default: NOT_REACHED();
    case DIAGDIR_NE:
      do {
        TileIndex tile_cur = tile;
 
        for (uint w_cur = w; w_cur != 0; --w_cur) {
          if (GB(*p, 0, 4) >= TileHeight(tile_cur)) SetTileHeight(tile_cur, GB(*p, 0, 4));
          p++;
          tile_cur++;
        }
        tile += TileDiffXY(0, 1);
      } while (--h != 0);
      break;
 
    case DIAGDIR_SE:
      do {
        TileIndex tile_cur = tile;
 
        for (uint h_cur = h; h_cur != 0; --h_cur) {
          if (GB(*p, 0, 4) >= TileHeight(tile_cur)) SetTileHeight(tile_cur, GB(*p, 0, 4));
          p++;
          tile_cur += TileDiffXY(0, 1);
        }
        tile += TileDiffXY(1, 0);
      } while (--w != 0);
      break;
 
    case DIAGDIR_SW:
      tile += TileDiffXY(w - 1, 0);
      do {
        TileIndex tile_cur = tile;
 
        for (uint w_cur = w; w_cur != 0; --w_cur) {
          if (GB(*p, 0, 4) >= TileHeight(tile_cur)) SetTileHeight(tile_cur, GB(*p, 0, 4));
          p++;
          tile_cur--;
        }
        tile += TileDiffXY(0, 1);
      } while (--h != 0);
      break;
 
    case DIAGDIR_NW:
      tile += TileDiffXY(0, h - 1);
      do {
        TileIndex tile_cur = tile;
 
        for (uint h_cur = h; h_cur != 0; --h_cur) {
          if (GB(*p, 0, 4) >= TileHeight(tile_cur)) SetTileHeight(tile_cur, GB(*p, 0, 4));
          p++;
          tile_cur -= TileDiffXY(0, 1);
        }
        tile += TileDiffXY(1, 0);
      } while (--w != 0);
      break;
  }
}
 
 
#include "table/genland.h"
 
static void CreateDesertOrRainForest(uint desert_tropic_line)
{
  TileIndex update_freq = MapSize() / 4;
  const TileIndexDiffC *data;
 
  for (TileIndex tile = 0; tile != MapSize(); ++tile) {
    if ((tile % update_freq) == 0) IncreaseGeneratingWorldProgress(GWP_LANDSCAPE);
 
    if (!IsValidTile(tile)) continue;
 
    for (data = _make_desert_or_rainforest_data;
        data != endof(_make_desert_or_rainforest_data); ++data) {
      TileIndex t = AddTileIndexDiffCWrap(tile, *data);
      if (t != INVALID_TILE && (TileHeight(t) >= desert_tropic_line || IsTileType(t, MP_WATER))) break;
    }
    if (data == endof(_make_desert_or_rainforest_data)) {
      SetTropicZone(tile, TROPICZONE_DESERT);
    }
  }
 
  for (uint i = 0; i != 256; i++) {
    if ((i % 64) == 0) IncreaseGeneratingWorldProgress(GWP_LANDSCAPE);
 
    RunTileLoop();
  }
 
  for (TileIndex tile = 0; tile != MapSize(); ++tile) {
    if ((tile % update_freq) == 0) IncreaseGeneratingWorldProgress(GWP_LANDSCAPE);
 
    if (!IsValidTile(tile)) continue;
 
    for (data = _make_desert_or_rainforest_data;
        data != endof(_make_desert_or_rainforest_data); ++data) {
      TileIndex t = AddTileIndexDiffCWrap(tile, *data);
      if (t != INVALID_TILE && IsTileType(t, MP_CLEAR) && IsClearGround(t, CLEAR_DESERT)) break;
    }
    if (data == endof(_make_desert_or_rainforest_data)) {
      SetTropicZone(tile, TROPICZONE_RAINFOREST);
    }
  }
}
 
static bool FindSpring(TileIndex tile, void *user_data)
{
  int referenceHeight;
  if (!IsTileFlat(tile, &referenceHeight) || IsWaterTile(tile)) return false;
 
  /* In the tropics rivers start in the rainforest. */
  if (_settings_game.game_creation.landscape == LT_TROPIC && GetTropicZone(tile) != TROPICZONE_RAINFOREST) return false;
 
  /* Are there enough higher tiles to warrant a 'spring'? */
  uint num = 0;
  for (int dx = -1; dx <= 1; dx++) {
    for (int dy = -1; dy <= 1; dy++) {
      TileIndex t = TileAddWrap(tile, dx, dy);
      if (t != INVALID_TILE && GetTileMaxZ(t) > referenceHeight) num++;
    }
  }
 
  if (num < 4) return false;
 
  /* Are we near the top of a hill? */
  for (int dx = -16; dx <= 16; dx++) {
    for (int dy = -16; dy <= 16; dy++) {
      TileIndex t = TileAddWrap(tile, dx, dy);
      if (t != INVALID_TILE && GetTileMaxZ(t) > referenceHeight + 2) return false;
    }
  }
 
  return true;
}
 
static bool MakeLake(TileIndex tile, void *user_data)
{
  uint height = *(uint*)user_data;
  if (!IsValidTile(tile) || TileHeight(tile) != height || !IsTileFlat(tile)) return false;
  if (_settings_game.game_creation.landscape == LT_TROPIC && GetTropicZone(tile) == TROPICZONE_DESERT) return false;
 
  for (DiagDirection d = DIAGDIR_BEGIN; d < DIAGDIR_END; d++) {
    TileIndex t2 = tile + TileOffsByDiagDir(d);
    if (IsWaterTile(t2)) {
      MakeRiver(tile, Random());
      MarkTileDirtyByTile(tile);
      /* Remove desert directly around the river tile. */
      TileIndex t = tile;
      CircularTileSearch(&t, RIVER_OFFSET_DESERT_DISTANCE, RiverModifyDesertZone, nullptr);
      return false;
    }
  }
 
  return false;
}
 
static bool RiverMakeWider(TileIndex tile, void *data)
{
  /* Don't expand into void tiles. */
  if (!IsValidTile(tile)) return false;
 
  /* If the tile is already sea or river, don't expand. */
  if (IsWaterTile(tile)) return false;
 
  /* If the tile is at height 0 after terraforming but the ocean hasn't flooded yet, don't build river. */
  if (GetTileMaxZ(tile) == 0) return false;
 
  TileIndex origin_tile = *(TileIndex *)data;;
  Slope cur_slope = GetTileSlope(tile);
  Slope desired_slope = GetTileSlope(origin_tile); // Initialize matching the origin tile as a shortcut if no terraforming is needed.
 
  /* Never flow uphill. */
  if (GetTileMaxZ(tile) > GetTileMaxZ(origin_tile)) return false;
 
  /* If the new tile can't hold a river tile, try terraforming. */
  if (!IsTileFlat(tile) && !IsInclinedSlope(cur_slope)) {
    /* Don't try to terraform steep slopes. */
    if (IsSteepSlope(cur_slope)) return false;
 
    bool flat_river_found = false;
    bool sloped_river_found = false;
 
    /* There are two common possibilities:
     * 1. River flat, adjacent tile has one corner lowered.
     * 2. River descending, adjacent tile has either one or three corners raised.
     */
 
    /* First, determine the desired slope based on adjacent river tiles. This doesn't necessarily match the origin tile for the CircularTileSearch. */
    for (DiagDirection d = DIAGDIR_BEGIN; d < DIAGDIR_END; d++) {
      TileIndex other_tile = TileAddByDiagDir(tile, d);
      Slope other_slope = GetTileSlope(other_tile);
 
      /* Only consider river tiles. */
      if (IsWaterTile(other_tile) && IsRiver(other_tile)) {
        /* If the adjacent river tile flows downhill, we need to check where we are relative to the slope. */
        if (IsInclinedSlope(other_slope) && GetTileMaxZ(tile) == GetTileMaxZ(other_tile)) {
          /* Check for a parallel slope. If we don't find one, we're above or below the slope instead. */
          if (GetInclinedSlopeDirection(other_slope) == ChangeDiagDir(d, DIAGDIRDIFF_90RIGHT) ||
              GetInclinedSlopeDirection(other_slope) == ChangeDiagDir(d, DIAGDIRDIFF_90LEFT)) {
            desired_slope = other_slope;
            sloped_river_found = true;
            break;
          }
        }
        /* If we find an adjacent river tile, remember it. We'll terraform to match it later if we don't find a slope. */
        if (IsTileFlat(tile)) flat_river_found = true;
      }
    }
    /* We didn't find either an inclined or flat river, so we're climbing the wrong slope. Bail out. */
    if (!sloped_river_found && !flat_river_found) return false;
 
    /* We didn't find an inclined river, but there is a flat river. */
    if (!sloped_river_found && flat_river_found) desired_slope = SLOPE_FLAT;
 
    /* Now that we know the desired slope, it's time to terraform! */
 
    /* If the river is flat and the adjacent tile has one corner lowered, we want to raise it. */
    if (desired_slope == SLOPE_FLAT && IsSlopeWithThreeCornersRaised(cur_slope)) {
      /* Make sure we're not affecting an existing river slope tile. */
      for (DiagDirection d = DIAGDIR_BEGIN; d < DIAGDIR_END; d++) {
        TileIndex other_tile = TileAddByDiagDir(tile, d);
        if (IsInclinedSlope(GetTileSlope(other_tile)) && IsWaterTile(other_tile)) return false;
      }
      Command<CMD_TERRAFORM_LAND>::Do(DC_EXEC | DC_AUTO, tile, ComplementSlope(cur_slope), true);
 
    /* If the river is descending and the adjacent tile has either one or three corners raised, we want to make it match the slope. */
    } else if (IsInclinedSlope(desired_slope)) {
      /* Don't break existing flat river tiles by terraforming under them. */
      DiagDirection river_direction = ReverseDiagDir(GetInclinedSlopeDirection(desired_slope));
 
      for (DiagDirDiff d = DIAGDIRDIFF_BEGIN; d < DIAGDIRDIFF_END; d++) {
        /* We don't care about downstream or upstream tiles, just the riverbanks. */
        if (d == DIAGDIRDIFF_SAME || d == DIAGDIRDIFF_REVERSE) continue;
 
        TileIndex other_tile = (TileAddByDiagDir(tile, ChangeDiagDir(river_direction, d)));
        if (IsWaterTile(other_tile) && IsRiver(other_tile) && IsTileFlat(other_tile)) return false;
      }
 
      /* Get the corners which are different between the current and desired slope. */
      Slope to_change = cur_slope ^ desired_slope;
 
      /* Lower unwanted corners first. If only one corner is raised, no corners need lowering. */
      if (!IsSlopeWithOneCornerRaised(cur_slope)) {
        to_change = to_change & ComplementSlope(desired_slope);
        Command<CMD_TERRAFORM_LAND>::Do(DC_EXEC | DC_AUTO, tile, to_change, false);
      }
 
      /* Now check the match and raise any corners needed. */
      cur_slope = GetTileSlope(tile);
      if (cur_slope != desired_slope && IsSlopeWithOneCornerRaised(cur_slope)) {
        to_change = cur_slope ^ desired_slope;
        Command<CMD_TERRAFORM_LAND>::Do(DC_EXEC | DC_AUTO, tile, to_change, true);
      }
    }
  }
  /* Update cur_slope after possibly terraforming. */
  cur_slope = GetTileSlope(tile);
 
  /* If the tile slope matches the desired slope, add a river tile. */
  if (cur_slope == desired_slope) {
    MakeRiver(tile, Random());
 
    /* Remove desert directly around the river tile. */
    TileIndex cur_tile = tile;
    MarkTileDirtyByTile(cur_tile);
    CircularTileSearch(&cur_tile, RIVER_OFFSET_DESERT_DISTANCE, RiverModifyDesertZone, nullptr);
  }
 
  /* Always return false to keep searching. */
  return false;
}
 
static bool FlowsDown(TileIndex begin, TileIndex end)
{
  assert(DistanceManhattan(begin, end) == 1);
 
  int heightBegin;
  int heightEnd;
  Slope slopeBegin = GetTileSlope(begin, &heightBegin);
  Slope slopeEnd   = GetTileSlope(end, &heightEnd);
 
  return heightEnd <= heightBegin &&
      /* Slope either is inclined or flat; rivers don't support other slopes. */
      (slopeEnd == SLOPE_FLAT || IsInclinedSlope(slopeEnd)) &&
      /* Slope continues, then it must be lower... or either end must be flat. */
      ((slopeEnd == slopeBegin && heightEnd < heightBegin) || slopeEnd == SLOPE_FLAT || slopeBegin == SLOPE_FLAT);
}
 
struct River_UserData {
  TileIndex spring; 
  bool main_river;  
};
 
/* AyStar callback for checking whether we reached our destination. */
static int32 River_EndNodeCheck(const AyStar *aystar, const OpenListNode *current)
{
  return current->path.node.tile == *(TileIndex*)aystar->user_target ? AYSTAR_FOUND_END_NODE : AYSTAR_DONE;
}
 
/* AyStar callback for getting the cost of the current node. */
static int32 River_CalculateG(AyStar *aystar, AyStarNode *current, OpenListNode *parent)
{
  return 1 + RandomRange(_settings_game.game_creation.river_route_random);
}
 
/* AyStar callback for getting the estimated cost to the destination. */
static int32 River_CalculateH(AyStar *aystar, AyStarNode *current, OpenListNode *parent)
{
  return DistanceManhattan(*(TileIndex*)aystar->user_target, current->tile);
}
 
/* AyStar callback for getting the neighbouring nodes of the given node. */
static void River_GetNeighbours(AyStar *aystar, OpenListNode *current)
{
  TileIndex tile = current->path.node.tile;
 
  aystar->num_neighbours = 0;
  for (DiagDirection d = DIAGDIR_BEGIN; d < DIAGDIR_END; d++) {
    TileIndex t2 = tile + TileOffsByDiagDir(d);
    if (IsValidTile(t2) && FlowsDown(tile, t2)) {
      aystar->neighbours[aystar->num_neighbours].tile = t2;
      aystar->neighbours[aystar->num_neighbours].direction = INVALID_TRACKDIR;
      aystar->num_neighbours++;
    }
  }
}
 
/* AyStar callback when an route has been found. */
static void River_FoundEndNode(AyStar *aystar, OpenListNode *current)
{
  River_UserData *data = (River_UserData *)aystar->user_data;
 
  /* First, build the river without worrying about its width. */
  uint cur_pos = 0;
  for (PathNode *path = &current->path; path != nullptr; path = path->parent, cur_pos++) {
    TileIndex tile = path->node.tile;
    if (!IsWaterTile(tile)) {
      MakeRiver(tile, Random());
      MarkTileDirtyByTile(tile);
      /* Remove desert directly around the river tile. */
      CircularTileSearch(&tile, RIVER_OFFSET_DESERT_DISTANCE, RiverModifyDesertZone, nullptr);
    }
  }
 
  /* If the river is a main river, go back along the path to widen it.
   * Don't make wide rivers if we're using the original landscape generator.
   */
  if (_settings_game.game_creation.land_generator != LG_ORIGINAL && data->main_river) {
    const uint long_river_length = _settings_game.game_creation.min_river_length * 4;
    uint current_river_length;
    uint radius;
 
    cur_pos = 0;
    for (PathNode *path = &current->path; path != nullptr; path = path->parent, cur_pos++) {
      TileIndex tile = path->node.tile;
 
      /* Check if we should widen river depending on how far we are away from the source. */
      current_river_length = DistanceManhattan(data->spring, tile);
      radius = std::min(3u, (current_river_length / (long_river_length / 3u)) + 1u);
 
      if (radius > 1) CircularTileSearch(&tile, radius + RandomRange(1), RiverMakeWider, (void *)&path->node.tile);
    }
  }
}
 
static const uint RIVER_HASH_SIZE = 8; 
 
static uint River_Hash(uint tile, uint dir)
{
  return GB(TileHash(TileX(tile), TileY(tile)), 0, RIVER_HASH_SIZE);
}
 
static void BuildRiver(TileIndex begin, TileIndex end, TileIndex spring, bool main_river)
{
  River_UserData user_data = { spring, main_river };
 
  AyStar finder = {};
  finder.CalculateG = River_CalculateG;
  finder.CalculateH = River_CalculateH;
  finder.GetNeighbours = River_GetNeighbours;
  finder.EndNodeCheck = River_EndNodeCheck;
  finder.FoundEndNode = River_FoundEndNode;
  finder.user_target = &end;
  finder.user_data = &user_data;
 
  finder.Init(River_Hash, 1 << RIVER_HASH_SIZE);
 
  AyStarNode start;
  start.tile = begin;
  start.direction = INVALID_TRACKDIR;
  finder.AddStartNode(&start, 0);
  finder.Main();
  finder.Free();
}
 
static std::tuple<bool, bool> FlowRiver(TileIndex spring, TileIndex begin, uint min_river_length)
{
# define SET_MARK(x) marks.insert(x)
# define IS_MARKED(x) (marks.find(x) != marks.end())
 
  uint height = TileHeight(begin);
 
  if (IsWaterTile(begin)) {
    return { DistanceManhattan(spring, begin) > min_river_length, GetTileZ(begin) == 0 };
  }
 
  std::set<TileIndex> marks;
  SET_MARK(begin);
 
  /* Breadth first search for the closest tile we can flow down to. */
  std::list<TileIndex> queue;
  queue.push_back(begin);
 
  bool found = false;
  uint count = 0; // Number of tiles considered; to be used for lake location guessing.
  TileIndex end;
  do {
    end = queue.front();
    queue.pop_front();
 
    uint height2 = TileHeight(end);
    if (IsTileFlat(end) && (height2 < height || (height2 == height && IsWaterTile(end)))) {
      found = true;
      break;
    }
 
    for (DiagDirection d = DIAGDIR_BEGIN; d < DIAGDIR_END; d++) {
      TileIndex t2 = end + TileOffsByDiagDir(d);
      if (IsValidTile(t2) && !IS_MARKED(t2) && FlowsDown(end, t2)) {
        SET_MARK(t2);
        count++;
        queue.push_back(t2);
      }
    }
  } while (!queue.empty());
 
  bool main_river = false;
  if (found) {
    /* Flow further down hill. */
    std::tie(found, main_river) = FlowRiver(spring, end, min_river_length);
  } else if (count > 32) {
    /* Maybe we can make a lake. Find the Nth of the considered tiles. */
    TileIndex lakeCenter = 0;
    int i = RandomRange(count - 1) + 1;
    std::set<TileIndex>::const_iterator cit = marks.begin();
    while (--i) cit++;
    lakeCenter = *cit;
 
    if (IsValidTile(lakeCenter) &&
        /* A river, or lake, can only be built on flat slopes. */
        IsTileFlat(lakeCenter) &&
        /* We want the lake to be built at the height of the river. */
        TileHeight(begin) == TileHeight(lakeCenter) &&
        /* We don't want the lake at the entry of the valley. */
        lakeCenter != begin &&
        /* We don't want lakes in the desert. */
        (_settings_game.game_creation.landscape != LT_TROPIC || GetTropicZone(lakeCenter) != TROPICZONE_DESERT) &&
        /* We only want a lake if the river is long enough. */
        DistanceManhattan(spring, lakeCenter) > min_river_length) {
      end = lakeCenter;
      MakeRiver(lakeCenter, Random());
      MarkTileDirtyByTile(lakeCenter);
      /* Remove desert directly around the river tile. */
      CircularTileSearch(&lakeCenter, RIVER_OFFSET_DESERT_DISTANCE, RiverModifyDesertZone, nullptr);
      lakeCenter = end;
      uint range = RandomRange(8) + 3;
      CircularTileSearch(&lakeCenter, range, MakeLake, &height);
      /* Call the search a second time so artefacts from going circular in one direction get (mostly) hidden. */
      lakeCenter = end;
      CircularTileSearch(&lakeCenter, range, MakeLake, &height);
      found = true;
    }
  }
 
  marks.clear();
  if (found) BuildRiver(begin, end, spring, main_river);
  return { found, main_river };
}
 
static void CreateRivers()
{
  int amount = _settings_game.game_creation.amount_of_rivers;
  if (amount == 0) return;
 
  uint wells = ScaleByMapSize(4 << _settings_game.game_creation.amount_of_rivers);
  const uint num_short_rivers = wells - std::max(1u, wells / 10);
  SetGeneratingWorldProgress(GWP_RIVER, wells + 256 / 64); // Include the tile loop calls below.
 
  /* Try to create long rivers. */
  for (; wells > num_short_rivers; wells--) {
    IncreaseGeneratingWorldProgress(GWP_RIVER);
    for (int tries = 0; tries < 512; tries++) {
      TileIndex t = RandomTile();
      if (!CircularTileSearch(&t, 8, FindSpring, nullptr)) continue;
      if (std::get<0>(FlowRiver(t, t, _settings_game.game_creation.min_river_length * 4))) break;
    }
  }
 
  /* Try to create short rivers. */
  for (; wells != 0; wells--) {
    IncreaseGeneratingWorldProgress(GWP_RIVER);
    for (int tries = 0; tries < 128; tries++) {
      TileIndex t = RandomTile();
      if (!CircularTileSearch(&t, 8, FindSpring, nullptr)) continue;
      if (std::get<0>(FlowRiver(t, t, _settings_game.game_creation.min_river_length))) break;
    }
  }
 
  /* Run tile loop to update the ground density. */
  for (uint i = 0; i != 256; i++) {
    if (i % 64 == 0) IncreaseGeneratingWorldProgress(GWP_RIVER);
    RunTileLoop();
  }
}
 
static uint CalculateCoverageLine(uint coverage, uint edge_multiplier)
{
  const DiagDirection neighbour_dir[] = {
    DIAGDIR_NE,
    DIAGDIR_SE,
    DIAGDIR_SW,
    DIAGDIR_NW,
  };
 
  /* Histogram of how many tiles per height level exist. */
  std::array<int, MAX_TILE_HEIGHT + 1> histogram = {};
  /* Histogram of how many neighbour tiles are lower than the tiles of the height level. */
  std::array<int, MAX_TILE_HEIGHT + 1> edge_histogram = {};
 
  /* Build a histogram of the map height. */
  for (TileIndex tile = 0; tile < MapSize(); tile++) {
    uint h = TileHeight(tile);
    histogram[h]++;
 
    if (edge_multiplier != 0) {
      /* Check if any of our neighbours is below us. */
      for (auto dir : neighbour_dir) {
        TileIndex neighbour_tile = AddTileIndexDiffCWrap(tile, TileIndexDiffCByDiagDir(dir));
        if (IsValidTile(neighbour_tile) && TileHeight(neighbour_tile) < h) {
          edge_histogram[h]++;
        }
      }
    }
  }
 
  /* The amount of land we have is the map size minus the first (sea) layer. */
  uint land_tiles = MapSizeX() * MapSizeY() - histogram[0];
  int best_score = land_tiles;
 
  /* Our goal is the coverage amount of the land-mass. */
  int goal_tiles = land_tiles * coverage / 100;
 
  /* We scan from top to bottom. */
  uint h = MAX_TILE_HEIGHT;
  uint best_h = h;
 
  int current_tiles = 0;
  for (; h > 0; h--) {
    current_tiles += histogram[h];
    int current_score = goal_tiles - current_tiles;
 
    /* Tropic grows from water and mountains into the desert. This is a
     * great visual, but it also means we* need to take into account how
     * much less desert tiles are being created if we are on this
     * height-level. We estimate this based on how many neighbouring
     * tiles are below us for a given length, assuming that is where
     * tropic is growing from.
     */
    if (edge_multiplier != 0 && h > 1) {
      /* From water tropic tiles grow for a few tiles land inward. */
      current_score -= edge_histogram[1] * edge_multiplier;
      /* Tropic tiles grow into the desert for a few tiles. */
      current_score -= edge_histogram[h] * edge_multiplier;
    }
 
    if (std::abs(current_score) < std::abs(best_score)) {
      best_score = current_score;
      best_h = h;
    }
 
    /* Always scan all height-levels, as h == 1 might give a better
     * score than any before. This is true for example with 0% desert
     * coverage. */
  }
 
  return best_h;
}
 
static void CalculateSnowLine()
{
  /* We do not have snow sprites on coastal tiles, so never allow "1" as height. */
  _settings_game.game_creation.snow_line_height = std::max(CalculateCoverageLine(_settings_game.game_creation.snow_coverage, 0), 2u);
}
 
static uint8 CalculateDesertLine()
{
  /* CalculateCoverageLine() runs from top to bottom, so we need to invert the coverage. */
  return CalculateCoverageLine(100 - _settings_game.game_creation.desert_coverage, 4);
}
 
void GenerateLandscape(byte mode)
{
  enum GenLandscapeSteps {
    GLS_HEIGHTMAP    =  3, 
    GLS_TERRAGENESIS =  5, 
    GLS_ORIGINAL     =  2, 
    GLS_TROPIC       = 12, 
    GLS_OTHER        =  0, 
  };
  uint steps = (_settings_game.game_creation.landscape == LT_TROPIC) ? GLS_TROPIC : GLS_OTHER;
 
  if (mode == GWM_HEIGHTMAP) {
    SetGeneratingWorldProgress(GWP_LANDSCAPE, steps + GLS_HEIGHTMAP);
    LoadHeightmap(_file_to_saveload.detail_ftype, _file_to_saveload.name.c_str());
    IncreaseGeneratingWorldProgress(GWP_LANDSCAPE);
  } else if (_settings_game.game_creation.land_generator == LG_TERRAGENESIS) {
    SetGeneratingWorldProgress(GWP_LANDSCAPE, steps + GLS_TERRAGENESIS);
    GenerateTerrainPerlin();
  } else {
    SetGeneratingWorldProgress(GWP_LANDSCAPE, steps + GLS_ORIGINAL);
    if (_settings_game.construction.freeform_edges) {
      for (uint x = 0; x < MapSizeX(); x++) MakeVoid(TileXY(x, 0));
      for (uint y = 0; y < MapSizeY(); y++) MakeVoid(TileXY(0, y));
    }
    switch (_settings_game.game_creation.landscape) {
      case LT_ARCTIC: {
        uint32 r = Random();
 
        for (uint i = ScaleByMapSize(GB(r, 0, 7) + 950); i != 0; --i) {
          GenerateTerrain(2, 0);
        }
 
        uint flag = GB(r, 7, 2) | 4;
        for (uint i = ScaleByMapSize(GB(r, 9, 7) + 450); i != 0; --i) {
          GenerateTerrain(4, flag);
        }
        break;
      }
 
      case LT_TROPIC: {
        uint32 r = Random();
 
        for (uint i = ScaleByMapSize(GB(r, 0, 7) + 170); i != 0; --i) {
          GenerateTerrain(0, 0);
        }
 
        uint flag = GB(r, 7, 2) | 4;
        for (uint i = ScaleByMapSize(GB(r, 9, 8) + 1700); i != 0; --i) {
          GenerateTerrain(0, flag);
        }
 
        flag ^= 2;
 
        for (uint i = ScaleByMapSize(GB(r, 17, 7) + 410); i != 0; --i) {
          GenerateTerrain(3, flag);
        }
        break;
      }
 
      default: {
        uint32 r = Random();
 
        assert(_settings_game.difficulty.quantity_sea_lakes != CUSTOM_SEA_LEVEL_NUMBER_DIFFICULTY);
        uint i = ScaleByMapSize(GB(r, 0, 7) + (3 - _settings_game.difficulty.quantity_sea_lakes) * 256 + 100);
        for (; i != 0; --i) {
          /* Make sure we do not overflow. */
          GenerateTerrain(Clamp(_settings_game.difficulty.terrain_type, 0, 3), 0);
        }
        break;
      }
    }
  }
 
  /* Do not call IncreaseGeneratingWorldProgress() before FixSlopes(),
   * it allows screen redraw. Drawing of broken slopes crashes the game */
  FixSlopes();
  MarkWholeScreenDirty();
  IncreaseGeneratingWorldProgress(GWP_LANDSCAPE);
 
  ConvertGroundTilesIntoWaterTiles();
  MarkWholeScreenDirty();
  IncreaseGeneratingWorldProgress(GWP_LANDSCAPE);
 
  switch (_settings_game.game_creation.landscape) {
    case LT_ARCTIC:
      CalculateSnowLine();
      break;
 
    case LT_TROPIC: {
      uint desert_tropic_line = CalculateDesertLine();
      CreateDesertOrRainForest(desert_tropic_line);
      break;
    }
 
    default:
      break;
  }
 
  CreateRivers();
}
 
void OnTick_Town();
void OnTick_Trees();
void OnTick_Station();
void OnTick_Industry();
 
void OnTick_Companies();
void OnTick_LinkGraph();
 
void CallLandscapeTick()
{
  {
    PerformanceAccumulator framerate(PFE_GL_LANDSCAPE);
 
    OnTick_Town();
    OnTick_Trees();
    OnTick_Station();
    OnTick_Industry();
  }
 
  OnTick_Companies();
  OnTick_LinkGraph();
}