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Bin no_trees_on_this_level, use exp. decay away from snow line.

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Probability of placing an arctic tree is now an exponential decay
function of height distance from the snow line, instead of the previous
50% blocks.
This results in a more gradual thinning out of arctic trees in
each direction.
The algorithm is: p = exp(-3 * distance / range_setting),
using a rather crude approximation of the exponential function.

The no_trees_on_this_level setting is not really useful, and its
dual behaviour to disallow discrete height levels and turn on the
snow line behaviour is unintuitive.
Replace it with a simple on/off setting.
pull/3/head
Jonathan G Rennison 9 years ago
parent 3b120c6cbd
commit 381d11096f
3 changed files with 75 additions and 32 deletions
Show Stats Download Patch File Download Diff File

2
src/settings_type.h
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@ -311,7 +311,7 @@ struct ConstructionSettings {
bool freeform_edges; ///< allow terraforming the tiles at the map edges
uint8 extra_tree_placement; ///< (dis)allow building extra trees in-game
uint8 trees_around_snow_line_range; ///< range around snowline for mixed and arctic forest.
uint32 no_trees_on_this_level; ///< option to avoid growth of trees on certain tile level.
bool trees_around_snow_line_enabled; ///< enable mixed and arctic forest around snowline, and no trees above snowline
uint8 command_pause_level; ///< level/amount of commands that can't be executed while paused
uint32 terraform_per_64k_frames; ///< how many tile heights may, over a long period, be terraformed per 65536 frames?

21
src/table/settings.ini
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@ -2310,23 +2310,22 @@ strhelp = STR_CONFIG_SETTING_EXTRA_TREE_PLACEMENT_HELPTEXT
strval = STR_CONFIG_SETTING_EXTRA_TREE_PLACEMENT_NONE
cat = SC_BASIC
[SDT_VAR]
[SDT_BOOL]
base = GameSettings
var = construction.trees_around_snow_line_range
type = SLE_UINT8
def = 0
min = 0
max = 15
var = construction.trees_around_snow_line_enabled
def = true
cat = SC_BASIC
patxname = ""everest_treeline.construction.trees_around_snow_line_enabled""
[SDT_VAR]
base = GameSettings
var = construction.no_trees_on_this_level
type = SLE_UINT32
def = 0
min = 0
max = UINT32_MAX
var = construction.trees_around_snow_line_range
type = SLE_UINT8
def = 8
min = 1
max = 20
cat = SC_BASIC
patxname = ""everest_treeline.construction.trees_around_snow_line_range""
[SDT_VAR]
base = GameSettings

84
src/tree_cmd.cpp
Unescape Escape View File

@ -118,6 +118,50 @@ static void PlantTreesOnTile(TileIndex tile, TreeType treetype, uint count, uint
MakeTree(tile, treetype, count, growth, ground, density);
}
/**
* Previous value of _settings_game.construction.trees_around_snow_line_range
* used to calculate _arctic_tree_occurance
*/
static uint8 _previous_trees_around_snow_line_range = 255;
/**
* Array of probabilities for artic trees to appear,
* by normalised distance from snow line
*/
static uint8 _arctic_tree_occurance[24];
/** Recalculate _arctic_tree_occurance */
static void RecalculateArcticTreeOccuranceArray()
{
/*
* Approximate: 256 * exp(-3 * distance / range)
* By using:
* 256 * ((1 + (-3 * distance / range) / 6) ** 6)
* ((256 - (128 * distance / range)) ** 6) >> (5 * 8);
*/
uint8 range = _settings_game.construction.trees_around_snow_line_range;
_previous_trees_around_snow_line_range = range;
_arctic_tree_occurance[0] = 255;
uint i = 1;
for (; i < lengthof(_arctic_tree_occurance); i++) {
if (range == 0) break;
uint x = 256 - ((128 * i) / range);
uint32 output = x;
output *= x;
output *= x;
output *= x;
output >>= 16;
output *= x;
output *= x;
output >>= 24;
if (output == 0) break;
_arctic_tree_occurance[i] = output;
}
for (; i < lengthof(_arctic_tree_occurance); i++) {
_arctic_tree_occurance[i] = 0;
}
}
/**
* Get a random TreeType for the given tile based on a given seed
*
@ -131,33 +175,33 @@ static void PlantTreesOnTile(TileIndex tile, TreeType treetype, uint count, uint
*/
static TreeType GetRandomTreeType(TileIndex tile, uint seed)
{
/* no_trees_on_this_level example: 0xDC96521 is no trees on z levels 13,12,9,6,5,2,1. Set to 0 gives you original gameplay. (See openttd.cfg) */
uint32 no_tree = _settings_game.construction.no_trees_on_this_level;
byte range = _settings_game.construction.trees_around_snow_line_range;
switch (_settings_game.game_creation.landscape) {
case LT_TEMPERATE:
if (no_tree == 0) return (TreeType)(seed * TREE_COUNT_TEMPERATE / 256 + TREE_TEMPERATE);
return (TreeType)(seed * TREE_COUNT_TEMPERATE / 256 + TREE_TEMPERATE);
case LT_ARCTIC: {
if (no_tree == 0) return (TreeType)(seed * TREE_COUNT_SUB_ARCTIC / 256 + TREE_SUB_ARCTIC);
if (!_settings_game.construction.trees_around_snow_line_enabled) {
return (TreeType)(seed * TREE_COUNT_SUB_ARCTIC / 256 + TREE_SUB_ARCTIC);
}
int z = GetTileZ(tile);
if (z > _settings_game.game_creation.snow_line_height + (2 * range)) return TREE_INVALID; // Above tree line.
uint8 range = _settings_game.construction.trees_around_snow_line_range;
if (range != _previous_trees_around_snow_line_range) RecalculateArcticTreeOccuranceArray();
/* no_trees_on_this_level */
for (; no_tree != 0;) {
if ((int)(no_tree & 0xF) == z) return TREE_INVALID;
no_tree = no_tree >> 4;
int z = GetTileZ(tile);
int height_above_snow_line = z - _settings_game.game_creation.snow_line_height;
uint normalised_distance = (height_above_snow_line < 0) ? -height_above_snow_line : height_above_snow_line + 1;
bool arctic_tree = false;
if (normalised_distance < lengthof(_arctic_tree_occurance)) {
uint adjusted_seed = (seed ^ tile) & 0xFF;
arctic_tree = adjusted_seed < _arctic_tree_occurance[normalised_distance];
}
if (z > (int)_settings_game.game_creation.snow_line_height - range) {
/* Below snow level mixed forest. Above is Arctic trees and thinning out. */
if (z < _settings_game.game_creation.snow_line_height) {
return (seed & 1) ? (TreeType)(seed * TREE_COUNT_SUB_ARCTIC / 256 + TREE_SUB_ARCTIC) : (TreeType)(seed * TREE_COUNT_TEMPERATE / 256 + TREE_TEMPERATE);
} else {
return (seed & 1) ? TREE_INVALID : (TreeType)(seed * TREE_COUNT_SUB_ARCTIC / 256 + TREE_SUB_ARCTIC);
}
if (height_above_snow_line < 0) {
/* Below snow level mixed forest. */
return (arctic_tree) ? (TreeType)(seed * TREE_COUNT_SUB_ARCTIC / 256 + TREE_SUB_ARCTIC) : (TreeType)(seed * TREE_COUNT_TEMPERATE / 256 + TREE_TEMPERATE);
} else {
/* Above is Arctic trees and thinning out. */
return (arctic_tree) ? (TreeType)(seed * TREE_COUNT_SUB_ARCTIC / 256 + TREE_SUB_ARCTIC) : TREE_INVALID;
}
return (TreeType)(seed * TREE_COUNT_TEMPERATE / 256 + TREE_TEMPERATE);
}
case LT_TROPIC:
switch (GetTropicZone(tile)) {

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