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Change: Eliminate small seas instead of ending rivers there (#14797)

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This commit is contained in:
Tyler Trahan
2025-12-04 10:55:13 -05:00
committed by GitHub
parent bd338d6e42
commit bca8913d1d
1 changed files with 56 additions and 2 deletions
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58
src/landscape.cpp
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@@ -1326,6 +1326,39 @@ bool RiverFlowsDown(TileIndex begin, TileIndex end)
return slope_end == SLOPE_FLAT || slope_begin == SLOPE_FLAT; return slope_end == SLOPE_FLAT || slope_begin == SLOPE_FLAT;
} }
/**
* Find the size of a patch of connected sea tiles.
* @param tile The starting tile to search.
* @param sea The set of sea tiles found.
* @param limit How many tiles to find before cutting the search short.
* @return True iff we found a map edge and broke out early, otherwise false (use the sea parameter as the output count/tile set).
*/
static bool CountConnectedSeaTiles(TileIndex tile, std::unordered_set<TileIndex> &sea, const uint limit)
{
/* This tile might not be sea. */
if (!IsWaterTile(tile) || GetWaterClass(tile) != WaterClass::Sea || !IsTileFlat(tile)) return false;
/* If we've found an edge tile, we are "connected to the sea outside the map." */
if (DistanceFromEdge(tile) <= 1) return true;
/* We have now evaluated this tile and don't want to check it again. */
sea.insert(tile);
/* We might want to cut our search short if the size of the sea is "big enough".
* Count this tile but don't check its neighbors. */
if (sea.size() > limit) return false;
/* Count adjacent tiles using recusion. */
for (DiagDirection d = DIAGDIR_BEGIN; d < DIAGDIR_END; d++) {
TileIndex t = tile + TileOffsByDiagDir(d);
if (IsValidTile(t) && !sea.contains(t)) {
if (CountConnectedSeaTiles(t, sea, limit)) return true;
}
}
return false;
}
/** /**
* Try to flow the river down from a given begin. * Try to flow the river down from a given begin.
* @param spring The springing point of the river. * @param spring The springing point of the river.
@@ -1358,8 +1391,29 @@ static std::tuple<bool, bool> FlowRiver(TileIndex spring, TileIndex begin, uint
int height_end; int height_end;
if (IsTileFlat(end, &height_end) && (height_end < height_begin || (height_end == height_begin && IsWaterTile(end)))) { if (IsTileFlat(end, &height_end) && (height_end < height_begin || (height_end == height_begin && IsWaterTile(end)))) {
found = true; if (IsWaterTile(end) && GetWaterClass(end) == WaterClass::Sea) {
break; /* If we've found the sea, make sure it's large enough. Scale by the map size but set a cap to avoid performance issues on large maps. */
const uint MAX_SEA_SIZE_THRESHOLD = 1024;
const uint SEA_SIZE_THRESHOLD = std::min(static_cast<uint>(2 * std::sqrt(Map::SizeX() * Map::SizeY())), MAX_SEA_SIZE_THRESHOLD);
std::unordered_set<TileIndex> sea;
/* Count the connected tiles, if the sea is large we can end the river here. */
bool found_edge = CountConnectedSeaTiles(end, sea, SEA_SIZE_THRESHOLD);
if (found_edge || sea.size() > SEA_SIZE_THRESHOLD) {
found = true;
break;
} else {
/* Sea is too small, flatten it so the river keeps looking or forms a lake / wetland. */
for (TileIndex sea_tile : sea) {
Command<CMD_TERRAFORM_LAND>::Do(DoCommandFlag::Execute, sea_tile, SLOPE_ELEVATED, false);
Slope slope = ComplementSlope(GetTileSlope(sea_tile));
Command<CMD_TERRAFORM_LAND>::Do(DoCommandFlag::Execute, sea_tile, slope, true);
}
}
} else {
/* We've found a river. */
found = true;
break;
}
} }
for (DiagDirection d = DIAGDIR_BEGIN; d < DIAGDIR_END; d++) { for (DiagDirection d = DIAGDIR_BEGIN; d < DIAGDIR_END; d++) {