Fix 07fba75: Immediately convert terraformed ground tiles into water tiles during river generation

src/landscape.cpp

@@ -1043,6 +1043,20 @@ static bool MakeLake(TileIndex tile, void *user_data)
 	return false;
 }
 
+bool _river_terraform = false;
+
+/**
+ * Terraform land around river.
+ * @param tile tile to terraform
+ * @param slope corners to terraform (SLOPE_xxx)
+ * @param dir_up direction; eg up (true) or down (false)
+ */
+static void RiverTerraform(TileIndex tile, Slope slope, bool dir_up)
+{
+	AutoRestoreBackup old_river_terraform(_river_terraform, true);
+	Command<CMD_TERRAFORM_LAND>::Do(DC_EXEC | DC_AUTO, tile, slope, dir_up);
+}
+
 /**
  * Widen a river by expanding into adjacent tiles via circular tile search.
  * @param tile The tile to try expanding the river into.
@@ -1057,9 +1071,6 @@ static bool RiverMakeWider(TileIndex tile, void *user_data)
 	/* 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 = *static_cast<TileIndex *>(user_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.
@@ -1116,7 +1127,7 @@ static bool RiverMakeWider(TileIndex tile, void *user_data)
 				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);
+			RiverTerraform(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)) {
@@ -1137,14 +1148,14 @@ static bool RiverMakeWider(TileIndex tile, void *user_data)
 			/* 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);
+				RiverTerraform(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);
+				RiverTerraform(tile, to_change, true);
 			}
 		}
 		/* Update cur_slope after possibly terraforming. */
@@ -1161,7 +1172,7 @@ static bool RiverMakeWider(TileIndex tile, void *user_data)
 		/* Don't look outside the map. */
 		if (!IsValidTile(upstream_tile) || !IsValidTile(downstream_tile)) return false;
 
-		/* Downstream might be new ocean created by our terraforming, and it hasn't flooded yet. */
+		/* Downstream might be new ocean created by our terraforming. */
 		bool downstream_is_ocean = GetTileZ(downstream_tile) == 0 && (GetTileSlope(downstream_tile) == SLOPE_FLAT || IsSlopeWithOneCornerRaised(GetTileSlope(downstream_tile)));
 
 		/* If downstream is dry, flat, and not ocean, try making it a river tile. */
@@ -1422,9 +1433,6 @@ static void CreateRivers()
 		}
 	}
 
-	/* Widening rivers may have left some tiles requiring to be watered. */
-	ConvertGroundTilesIntoWaterTiles();
-
 	/* Run tile loop to update the ground density. */
 	for (uint i = 0; i != TILE_UPDATE_FREQUENCY; i++) {
 		if (i % 64 == 0) IncreaseGeneratingWorldProgress(GWP_RIVER);

src/landscape.h

@@ -137,5 +137,6 @@ void RunTileLoop();
 
 void InitializeLandscape();
 bool GenerateLandscape(uint8_t mode);
+extern bool _river_terraform;
 
 #endif /* LANDSCAPE_H */

src/terraform_cmd.cpp

@@ -19,6 +19,8 @@
 #include "core/backup_type.hpp"
 #include "terraform_cmd.h"
 #include "landscape_cmd.h"
+#include "water.h"
+#include "landscape.h"
 
 #include "table/strings.h"
 
@@ -297,6 +299,14 @@ std::tuple<CommandCost, Money, TileIndex> CmdTerraformLand(DoCommandFlag flags,
 			SetTileHeight(t, (uint)height);
 		}
 
+		if (_river_terraform) {
+			for (const auto &t : ts.dirty_tiles) {
+				/* Immediately convert ground tiles into water tiles during river generation. */
+				ConvertGroundTileIntoWaterTile(t);
+				MarkTileDirtyByTile(t);
+			}
+		}
+
 		if (c != nullptr) c->terraform_limit -= (uint32_t)ts.tile_to_new_height.size() << 16;
 	}
 	return { total_cost, 0, total_cost.Succeeded() ? tile : INVALID_TILE };

src/water.h

@@ -29,6 +29,7 @@ void ClearNeighbourNonFloodingStates(TileIndex tile);
 void TileLoop_Water(TileIndex tile);
 bool FloodHalftile(TileIndex t);
 
+void ConvertGroundTileIntoWaterTile(TileIndex tile);
 void ConvertGroundTilesIntoWaterTiles();
 
 void DrawShipDepotSprite(int x, int y, Axis axis, DepotPart part);

src/water_cmd.cpp

@@ -1297,9 +1297,10 @@ void TileLoop_Water(TileIndex tile)
 	}
 }
 
-void ConvertGroundTilesIntoWaterTiles()
+void ConvertGroundTileIntoWaterTile(TileIndex tile)
 {
-	for (const auto tile : Map::Iterate()) {
+	assert(tile < Map::Size());
+
 	auto [slope, z] = GetTileSlopeZ(tile);
 	if (IsTileType(tile, MP_CLEAR) && z == 0) {
 		/* Make both water for tiles at level 0
@@ -1329,6 +1330,12 @@ void ConvertGroundTilesIntoWaterTiles()
 				break;
 		}
 	}
+}
+
+void ConvertGroundTilesIntoWaterTiles()
+{
+	for (const auto tile : Map::Iterate()) {
+		ConvertGroundTileIntoWaterTile(tile);
 	}
 }