Refactored [sub-]cell availability logic in IPositionable & ActorMap

Moved the logic from IPositionable.CanEnterCell & integrated sub-cell selection.
Added IPositionable.IsMovingFrom(CPos location, int subCell = -1) - to detect transient actors
Renamed IPositionable.{GetDesiredSubcell => GetAvailableSubcell} - since it checks for available sub-cells
Reduced IPositionable.CanEnterCell to one method that usually uses IPositionable.GetAvailableSubcell
Added actor checking to ActorMap.{HasFreeSubCell, FreeSubCell, AnyUnitsAt} - used by [sub-]cell availability logic

OpenRA.Game/Traits/TraitsInterfaces.cs

@@ -180,9 +180,9 @@ namespace OpenRA.Traits
 
 	public interface IPositionable : IOccupySpace
 	{
-		bool CanEnterCell(CPos location);
+		bool IsMovingFrom(CPos location, int subCell = -1);
-		bool CanEnterCell(CPos location, Actor ignoreActor, bool checkTransientActors);
+		bool CanEnterCell(CPos location, Actor ignoreActor = null, bool checkTransientActors = true);
-		int GetDesiredSubcell(CPos a, Actor ignoreActor);
+		int GetAvailableSubcell(CPos location, int preferredSubCell = -1, Actor ignoreActor = null, bool checkTransientActors = true);
 		void SetPosition(Actor self, CPos cell, int subCell = -1);
 		void SetPosition(Actor self, WPos pos);
 		void SetVisualPosition(Actor self, WPos pos);

OpenRA.Game/Traits/World/ActorMap.cs

@@ -83,35 +83,68 @@ namespace OpenRA.Traits
 					yield return i.Actor;
 		}
 
-		public bool HasFreeSubCell(CPos a)
+		public bool HasFreeSubCell(CPos a, bool checkTransient = true)
 		{
-			return FreeSubCell(a) >= 0;
+			return FreeSubCell(a, -1, checkTransient) >= 0;
 		}
 
-		public int FreeSubCell(CPos a, int preferredSubCell = -1)
+		public int FreeSubCell(CPos a, int preferredSubCell = -1, bool checkTransient = true)
 		{
-			if (preferredSubCell >= 0 && !AnyUnitsAt(a, preferredSubCell))
+			if (preferredSubCell >= 0 && !AnyUnitsAt(a, preferredSubCell, checkTransient))
 				return preferredSubCell;
 
 			if (!AnyUnitsAt(a))
 				return map.SubCellDefaultIndex;
 
 			for (var i = 1; i < map.SubCellOffsets.Length; i++)
-				if (!AnyUnitsAt(a, i))
+				if (i != preferredSubCell && !AnyUnitsAt(a, i, checkTransient))
 					return i;
 			return -1;
 		}
 
+		public int FreeSubCell(CPos a, int preferredSubCell, Func<Actor, bool> checkIfBlocker)
+		{
+			if (preferredSubCell >= 0 && !AnyUnitsAt(a, preferredSubCell, checkIfBlocker))
+				return preferredSubCell;
+
+			if (!AnyUnitsAt(a))
+				return map.SubCellDefaultIndex;
+
+			for (var i = 1; i < map.SubCellOffsets.Length; i++)
+				if (i != preferredSubCell && !AnyUnitsAt(a, i, checkIfBlocker))
+					return i;
+			return -1;
+		}
+
+		// NOTE: does not check transients, but checks aircraft
 		public bool AnyUnitsAt(CPos a)
 		{
 			return influence[a] != null;
 		}
 
-		public bool AnyUnitsAt(CPos a, int sub)
+		// NOTE: can not check aircraft
+		public bool AnyUnitsAt(CPos a, int sub, bool checkTransient = true)
 		{
 			for (var i = influence[a]; i != null; i = i.Next)
-				if (i.SubCell == sub || i.SubCell == 0)
+				if (sub <= 0 || i.SubCell == sub || i.SubCell == 0)
-					return true;
+				{
+					if (checkTransient)
+						return true;
+					var pos = i.Actor.TraitOrDefault<IPositionable>();
+					if (pos == null || !pos.IsMovingFrom(a, i.SubCell))
+						return true;
+				}
+
+			return false;
+		}
+
+		// NOTE: can not check aircraft
+		public bool AnyUnitsAt(CPos a, int sub, Func<Actor, bool> withCondition)
+		{
+			for (var i = influence[a]; i != null; i = i.Next)
+				if (sub <= 0 || i.SubCell == sub || i.SubCell == 0)
+					if (withCondition(i.Actor))
+						return true;
 
 			return false;
 		}

OpenRA.Mods.RA/Activities/UnloadCargo.cs

@@ -38,7 +38,7 @@ namespace OpenRA.Mods.RA.Activities
 
 			return cargo.CurrentAdjacentCells
 				.Shuffle(self.World.SharedRandom)
-				.Select(c => Pair.New(c, pos.GetDesiredSubcell(c, null)))
+				.Select(c => Pair.New(c, pos.GetAvailableSubcell(c, -1, null)))
 				.Cast<Pair<CPos, int>?>()
 				.FirstOrDefault(s => s.Value.Second >= 0);
 		}

OpenRA.Mods.RA/Air/Aircraft.cs

@@ -198,10 +198,10 @@ namespace OpenRA.Mods.RA.Air
 			return info.RearmBuildings.Contains(a.Info.Name)
 				|| info.RepairBuildings.Contains(a.Info.Name);
 		}
-		
+
-		public int GetDesiredSubcell(CPos a, Actor ignoreActor) { return -1; } // does not use any subcell
+		public bool IsMovingFrom(CPos location, int subCell = -1) { return false; } // TODO: handle landing
-		public bool CanEnterCell(CPos location) { return true; }
+		public int GetAvailableSubcell(CPos a, int preferredSubCell = -1, Actor ignoreActor = null, bool checkTransientActors = true) { return -1; } // does not use any subcell
-		public bool CanEnterCell(CPos cell, Actor ignoreActor, bool checkTransientActors) { return true; }
+		public bool CanEnterCell(CPos cell, Actor ignoreActor = null, bool checkTransientActors = true) { return true; }
 
 		public int MovementSpeed
 		{

OpenRA.Mods.RA/Crate.cs

@@ -95,27 +95,30 @@ namespace OpenRA.Mods.RA
 		public void SetPosition(Actor self, WPos pos) { SetPosition(self, self.World.Map.CellContaining(pos)); }
 		public void SetVisualPosition(Actor self, WPos pos) { SetPosition(self, self.World.Map.CellContaining(pos)); }
 
-		public bool CanEnterCell(CPos cell, Actor ignoreActor, bool checkTransientActors)
+		public bool IsMovingFrom(CPos location, int subCell = -1) { return false; }
+		public int GetAvailableSubcell(CPos cell, int preferredSubCell = -1, Actor ignoreActor = null, bool checkTransientActors = true)
 		{
-			if (!self.World.Map.Contains(cell)) return false;
+			if (!self.World.Map.Contains(cell)) return -1;
 
 			var type = self.World.Map.GetTerrainInfo(cell).Type;
 			if (!info.TerrainTypes.Contains(type))
-				return false;
+				return -1;
 
 			if (self.World.WorldActor.Trait<BuildingInfluence>().GetBuildingAt(cell) != null)
-				return false;
+				return -1;
 
 			if (!checkTransientActors)
-				return true;
+				return 0;
 
 			return !self.World.ActorMap.GetUnitsAt(cell)
 				.Where(x => x != ignoreActor)
-				.Any();
+				.Any() ? 0 : -1;
 		}
 
-		public int GetDesiredSubcell(CPos a, Actor ignoreActor) { return CanEnterCell(a, ignoreActor, true) ? 0 : -1; }
+		public bool CanEnterCell(CPos a, Actor ignoreActor = null, bool checkTransientActors = true)
-		public bool CanEnterCell(CPos cell) { return CanEnterCell(cell, null, true); }
+		{
+			return GetAvailableSubcell(a, -1, ignoreActor, checkTransientActors) >= 0;
+		}
 
 		public void SetPosition(Actor self, CPos cell, int subCell = -1)
 		{

OpenRA.Mods.RA/Husk.cs

@@ -53,24 +53,28 @@ namespace OpenRA.Mods.RA
 		}
 
 		public IEnumerable<Pair<CPos, int>> OccupiedCells() { yield return Pair.New(TopLeft, 0); }
-		public bool CanEnterCell(CPos cell, Actor ignoreActor, bool checkTransientActors)
+		public bool IsMovingFrom(CPos location, int subCell = -1) { return false; }
+		public int GetAvailableSubcell(CPos cell, int preferredSubCell = -1, Actor ignoreActor = null, bool checkTransientActors = true)
 		{
 			if (!self.World.Map.Contains(cell))
-				return false;
+				return -1;
 
 			if (!info.AllowedTerrain.Contains(self.World.Map.GetTerrainInfo(cell).Type))
-				return false;
+				return -1;
 
 			if (!checkTransientActors)
-				return true;
+				return 0;
 
 			return !self.World.ActorMap.GetUnitsAt(cell)
 				.Where(x => x != ignoreActor)
-				.Any();
+				.Any() ? 0 : -1;
+		}
+
+		public bool CanEnterCell(CPos a, Actor ignoreActor = null, bool checkTransientActors = true)
+		{
+			return GetAvailableSubcell(a, -1, ignoreActor, checkTransientActors) >= 0;
 		}
 
-		public int GetDesiredSubcell(CPos a, Actor ignoreActor) { return CanEnterCell(a, ignoreActor, true) ? 0 : -1; }
-		public bool CanEnterCell(CPos cell) { return CanEnterCell(cell, null, true); }
 		public void SetPosition(Actor self, CPos cell, int subCell = -1) { SetPosition(self, self.World.Map.CenterOfCell(cell)); }
 
 		public void SetVisualPosition(Actor self, WPos pos)

OpenRA.Mods.RA/Move/Mobile.cs

@@ -206,6 +206,45 @@ namespace OpenRA.Mods.RA.Move
 			return true;
 		}
 
+		public int GetAvailableSubCell(World world, Actor self, CPos cell, int preferredSubCell = -1, Actor ignoreActor = null, CellConditions check = CellConditions.All)
+		{
+			if (MovementCostForCell(world, cell) == int.MaxValue)
+				return -1;
+
+			if (check.HasFlag(CellConditions.TransientActors))
+			{
+				var canIgnoreMovingAllies = self != null && !check.HasFlag(CellConditions.BlockedByMovers);
+				var needsCellExclusively = self == null || Crushes == null;
+
+				Func<Actor, bool> checkTransient = a =>
+				{
+					if (a == ignoreActor) return false;
+
+					// Neutral/enemy units are blockers. Allied units that are moving are not blockers.
+					if (canIgnoreMovingAllies && self.Owner.Stances[a.Owner] == Stance.Ally && IsMovingInMyDirection(self, a)) return false;
+					
+					// Non-sharable unit can enter a cell with shareable units only if it can crush all of them.
+					if (needsCellExclusively) return true;
+					if (!a.HasTrait<ICrushable>()) return true;
+					foreach (var crushable in a.TraitsImplementing<ICrushable>())
+						if (!crushable.CrushableBy(Crushes, self.Owner))
+							return true;
+
+					return false;
+				};
+
+				if (!SharesCell)
+					return world.ActorMap.AnyUnitsAt(cell, 0, checkTransient)? -1 : 0;
+
+				return world.ActorMap.FreeSubCell(cell, preferredSubCell, checkTransient);
+			}
+
+			if (!SharesCell)
+				return world.ActorMap.AnyUnitsAt(cell, 0)? -1 : 0;
+
+			return world.ActorMap.FreeSubCell(cell, preferredSubCell);
+		}
+
 		public int GetInitialFacing() { return InitialFacing; }
 	}
 
@@ -437,44 +476,18 @@ namespace OpenRA.Mods.RA.Move
 			}
 		}
 
-		bool IsDesiredSubcellNotBlocked(CPos a, int b, Actor ignoreActor)
+		public bool IsMovingFrom(CPos location, int subCell = -1)
 		{
-			var blockingActors = self.World.ActorMap.GetUnitsAt(a, b).Where(c => c != ignoreActor);
+			return toCell != location && __fromCell == location
-			if (blockingActors.Any())
+				&& (subCell == -1 || fromSubCell == subCell || subCell == 0 || fromSubCell == 0);
-			{
-				// Non-sharable unit can enter a cell with shareable units only if it can crush all of them
-				if (Info.Crushes == null)
-					return false;
-
-				if (blockingActors.Any(c => !(c.HasTrait<ICrushable>() &&
-						c.TraitsImplementing<ICrushable>().Any(d => d.CrushableBy(Info.Crushes, self.Owner)))))
-					return false;
-			}
-			return true;
 		}
 
-		public int GetDesiredSubcell(CPos a, Actor ignoreActor)
+		public int GetAvailableSubcell(CPos a, int preferredSubCell, Actor ignoreActor = null, bool checkTransientActors = true)
 		{
-			if (!Info.SharesCell)
+			return Info.GetAvailableSubCell(self.World, self, a, preferredSubCell, ignoreActor, checkTransientActors? CellConditions.All : CellConditions.None);
-				return 0;
-
-			// Prioritise the current subcell
-			if (IsDesiredSubcellNotBlocked(a, fromSubCell, ignoreActor))
-				return fromSubCell;
-
-			for (var i = 1; i < self.World.Map.SubCellOffsets.Length; i++)
-				if (IsDesiredSubcellNotBlocked(a, i, ignoreActor))
-					return i;
-
-			return -1;
 		}
 
-		public bool CanEnterCell(CPos p)
+		public bool CanEnterCell(CPos cell, Actor ignoreActor = null, bool checkTransientActors = true)
-		{
-			return CanEnterCell(p, null, true);
-		}
-
-		public bool CanEnterCell(CPos cell, Actor ignoreActor, bool checkTransientActors)
 		{
 			return Info.CanEnterCell(self.World, self, cell, ignoreActor, checkTransientActors ? CellConditions.All : CellConditions.BlockedByMovers);
 		}

OpenRA.Mods.RA/Move/Move.cs

@@ -245,7 +245,7 @@ namespace OpenRA.Mods.RA.Move
 			hasWaited = false;
 			path.RemoveAt(path.Count - 1);
 
-			var subCell = mobile.GetDesiredSubcell(nextCell, ignoreBuilding);
+			var subCell = mobile.GetAvailableSubcell(nextCell, -1, ignoreBuilding);
 			return Pair.New(nextCell, subCell);
 		}