Chunnel: Adjust z position of vehicles in chunnels to go "under" the water.

src/ground_vehicle.cpp

@@ -13,6 +13,8 @@
 #include "train.h"
 #include "roadveh.h"
 #include "depot_map.h"
+#include "tunnel_base.h"
+#include "slope_type.h"
 
 #include "safeguards.h"
 
@@ -280,6 +282,66 @@ bool GroundVehicle<T, Type>::IsChainInDepot() const
 	return true;
 }
 
+/**
+ * Updates vehicle's Z inclination inside a wormhole, where applicable.
+ */
+template <class T, VehicleType Type>
+void GroundVehicle<T, Type>::UpdateZPositionInWormhole()
+{
+	if (!IsTunnel(this->tile)) return;
+
+	const Tunnel *t = Tunnel::GetByTile(this->tile);
+	if (!t->is_chunnel) return;
+
+	TileIndex pos_tile = TileVirtXY(this->x_pos, this->y_pos);
+
+	ClrBit(this->gv_flags, GVF_GOINGUP_BIT);
+	ClrBit(this->gv_flags, GVF_GOINGDOWN_BIT);
+
+	if (pos_tile == t->tile_n || pos_tile == t->tile_s) {
+		this->z_pos = 0;
+		return;
+	}
+
+	int north_coord, south_coord, pos_coord;
+	bool going_north;
+	Slope slope_north;
+	if (t->tile_s - t->tile_n > MapMaxX()) {
+		// tunnel extends along Y axis (DIAGDIR_SE from north end), has same X values
+		north_coord = TileY(t->tile_n);
+		south_coord = TileY(t->tile_s);
+		pos_coord = TileY(pos_tile);
+		going_north = (this->direction == DIR_NW);
+		slope_north = SLOPE_NW;
+	} else {
+		// tunnel extends along X axis (DIAGDIR_SW from north end), has same Y values
+		north_coord = TileX(t->tile_n);
+		south_coord = TileX(t->tile_s);
+		pos_coord = TileX(pos_tile);
+		going_north = (this->direction == DIR_NE);
+		slope_north = SLOPE_NE;
+	}
+
+	Slope slope = SLOPE_FLAT;
+
+	int delta;
+	if ((delta = pos_coord - north_coord) <= 3) {
+		this->z_pos = TILE_HEIGHT * (delta == 3 ? -2 : -1);
+		if (delta != 2) {
+			slope = slope_north;
+			SetBit(this->gv_flags, going_north ? GVF_GOINGUP_BIT : GVF_GOINGDOWN_BIT);
+		}
+	} else if ((delta = south_coord - pos_coord) <= 3) {
+		this->z_pos = TILE_HEIGHT * (delta == 3 ? -2 : -1);
+		if (delta != 2) {
+			slope = SLOPE_ELEVATED ^ slope_north;
+			SetBit(this->gv_flags, going_north ? GVF_GOINGDOWN_BIT : GVF_GOINGUP_BIT);
+		}
+	}
+
+	if (slope != SLOPE_FLAT) this->z_pos += GetPartialPixelZ(this->x_pos & 0xF, this->y_pos & 0xF, slope);
+}
+
 /* Instantiation for Train */
 template struct GroundVehicle<Train, VEH_TRAIN>;
 /* Instantiation for RoadVehicle */

src/ground_vehicle.hpp

@@ -228,17 +228,21 @@ struct GroundVehicle : public SpecializedVehicle<T, Type> {
 		assert(this->z_pos == GetSlopePixelZ(this->x_pos, this->y_pos));
 	}
 
+	void UpdateZPositionInWormhole();
+
 	/**
 	 * Checks if the vehicle is in a slope and sets the required flags in that case.
 	 * @param new_tile True if the vehicle reached a new tile.
 	 * @param update_delta Indicates to also update the delta.
 	 * @return Old height of the vehicle.
 	 */
-	inline int UpdateInclination(bool new_tile, bool update_delta)
+	inline int UpdateInclination(bool new_tile, bool update_delta, bool in_wormhole = false)
 	{
 		int old_z = this->z_pos;
 
-		if (new_tile) {
+		if (in_wormhole) {
+			this->UpdateZPositionInWormhole();
+		} else if (new_tile) {
 			this->UpdateZPositionAndInclination();
 		} else {
 			this->UpdateZPosition();

src/roadveh_cmd.cpp

@@ -1184,6 +1184,7 @@ bool IndividualRoadVehicleController(RoadVehicle *v, const RoadVehicle *prev)
 			v->x_pos = gp.x;
 			v->y_pos = gp.y;
 			v->UpdatePosition();
+			RoadZPosAffectSpeed(v, v->UpdateInclination(false, false, true));
 			if (v->IsDrawn()) v->Vehicle::UpdateViewport(true);
 			return true;
 		}
@@ -1555,7 +1556,7 @@ again:
 	v->x_pos = x;
 	v->y_pos = y;
 	v->UpdatePosition();
-	RoadZPosAffectSpeed(v, v->UpdateInclination(false, true));
+	RoadZPosAffectSpeed(v, v->UpdateInclination(false, true, v->state == RVSB_WORMHOLE));
 	return true;
 }
 

src/train_cmd.cpp

@@ -1685,6 +1685,7 @@ static void UpdateStatusAfterSwap(Train *v)
 	}
 
 	v->UpdatePosition();
+	if (v->track == TRACK_BIT_WORMHOLE) v->UpdateInclination(false, false, true);
 	v->UpdateViewport(true, true);
 }
 
@@ -3903,6 +3904,15 @@ bool TrainController(Train *v, Vehicle *nomove, bool reverse)
 				v->x_pos = gp.x;
 				v->y_pos = gp.y;
 				v->UpdatePosition();
+				if (v->track == TRACK_BIT_WORMHOLE) {
+					/* update the Z position of the vehicle */
+					int old_z = v->UpdateInclination(false, false, true);
+
+					if (prev == NULL) {
+						/* This is the first vehicle in the train */
+						AffectSpeedByZChange(v, old_z);
+					}
+				}
 				if (v->IsDrawn()) v->Vehicle::UpdateViewport(true);
 				continue;
 			}
@@ -3919,7 +3929,7 @@ bool TrainController(Train *v, Vehicle *nomove, bool reverse)
 		}
 
 		/* update the Z position of the vehicle */
-		int old_z = v->UpdateInclination(gp.new_tile != gp.old_tile, false);
+		int old_z = v->UpdateInclination(gp.new_tile != gp.old_tile, false, v->track == TRACK_BIT_WORMHOLE);
 
 		if (prev == NULL) {
 			/* This is the first vehicle in the train */