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Fix: Don't block nearby river slope connection with terraform 

When two sloped rivers are adjacent to one another, RiverMakeWider's terraform could at times close the connection to one of the rivers.

Implemented a more robust method to deal with widening of inclined river slopes, by weighing in the consequences in advance to performing the terraform.
pull/13370/head
SamuXarick 2025-01-23 18:12:57 +00:00
parent 184621e64a
commit b1a5d181a0
1 changed files with 58 additions and 10 deletions
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68
src/landscape.cpp
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@ -1063,7 +1063,7 @@ static bool RiverMakeWider(TileIndex tile, void *user_data)
if (IsSteepSlope(cur_slope)) return false;
bool flat_river_found = false;
bool sloped_river_found = false;
std::vector<std::tuple<Slope, int, uint>> sloped_rivers;
/* There are two common possibilities:
* 1. River flat, adjacent tile has one corner lowered.
@ -1080,22 +1080,70 @@ static bool RiverMakeWider(TileIndex tile, void *user_data)
/* 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;
for (DiagDirDiff dir_diff : { DIAGDIRDIFF_90RIGHT, DIAGDIRDIFF_90LEFT }) {
DiagDirection other_d = ChangeDiagDir(d, dir_diff);
if (GetInclinedSlopeDirection(other_slope) == other_d) {
/* Calculate the length of the parallel slope. */
int length = 0;
TileIndex parallel_tile = other_tile;
for (;;) {
length++;
parallel_tile = AddTileIndexDiffCWrap(parallel_tile, TileIndexDiffCByDiagDir(d));
if (parallel_tile == INVALID_TILE) break;
if (!IsWaterTile(parallel_tile) || !IsRiver(parallel_tile)) break;
if (GetTileMaxZ(parallel_tile) != GetTileMaxZ(tile)) break;
Slope parallel_slope = GetTileSlope(parallel_tile);
if (!IsInclinedSlope(parallel_slope) || GetInclinedSlopeDirection(parallel_slope) != other_d) break;
}
/* Store the slope, its length, and distance to the origin tile. */
sloped_rivers.push_back(std::make_tuple(other_slope, length, DistanceManhattan(other_tile, origin_tile)));
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(other_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;
if (sloped_rivers.empty()) {
/* We didn't find either an inclined or flat river, so we're climbing the wrong slope. Bail out. */
if (!flat_river_found) return false;
/* We didn't find an inclined river, but there is a flat river. */
desired_slope = SLOPE_FLAT;
} else if (sloped_rivers.size() == 1) {
/* We found an inclined river. */
desired_slope = std::get<0>(sloped_rivers[0]);
} else {
/* We found two inclined rivers. */
assert(sloped_rivers.size() == 2);
/* Initialize slopes. */
auto &[short_slope, short_length, short_dist] = sloped_rivers[0];
[[maybe_unused]] auto &[_, wider_length, wider_dist] = sloped_rivers[1];
/* Swap values if needed. */
if (short_length > wider_length) {
std::swap(sloped_rivers[0], sloped_rivers[1]);
}
if (short_dist <= wider_dist && desired_slope != short_slope) {
int length_difference = wider_length - short_length;
/* If the lengths of both slopes are equal, do nothing.
* If one slope is shorter, decide whether to widen the shorter river slope at the cost of the longer one:
* - If the difference in lengths is 1, there's a 50% chance to widen the shorter slope.
* - If the difference in lengths is exactly 2, always widen the shorter slope to make them equal.
* - If the difference in lengths is greater than 2, always widen the shorter slope, but they will not be equal.
* For example, if the lengths are 1 and 4, widening will result in lengths of 2 and 3. */
if (length_difference == 1) {
if (Chance16(1, 2)) desired_slope = short_slope;
} else if (length_difference >= 2) {
desired_slope = short_slope;
}
}
}
/* Now that we know the desired slope, it's time to terraform! */