fix PlaceAlongSpaceEdges requirement

Assets/Engine/Runtime/Placement.cs

@@ -10,7 +10,7 @@ namespace EscapeRoomEngine.Engine.Runtime
         /// <summary>
         /// The placement position is always considered to be at <c>(0.5, 0.5)</c> relative to the placement.
         ///
-        /// <example>In a placement of size <c>(1, 1)</c>, the position is at the center of the placement. In a larger placement, the position is in the center of the bottom left square meter.</example>
+        /// <example>In a placement of size <c>(1, 1)</c>, the position is at the center of the placement. In a larger placement, the position is in the center of the bottom left square.</example>
         /// </summary>
         public Vector3Int position;
         public Vector2Int size;
@@ -31,6 +31,28 @@ namespace EscapeRoomEngine.Engine.Runtime
             }
         }
         
+        /// <summary>
+        /// Get the positions of the two back corners. The first one is just the position of the placement.
+        /// </summary>
+        /// <exception cref="ArgumentOutOfRangeException"></exception>
+        public (Vector3Int, Vector3Int) BackCorners {
+            get
+            {
+                var width = size.x - 1;
+                var horizontal = new Vector3Int(width, 0, 0);
+                var vertical = new Vector3Int(0, 0, width);
+                var otherCorner = orientation switch
+                {
+                    Orientation.North => position + horizontal,
+                    Orientation.East => position - vertical,
+                    Orientation.South => position - horizontal,
+                    Orientation.West => position + vertical,
+                    _ => throw new ArgumentOutOfRangeException()
+                };
+                return (position, otherCorner);
+            }
+        }
+        
         /// <summary>
         /// Create a set with every possible combination of position and orientation of placements that fit in a given space.
         /// The size of the placements are given by this placement.

Assets/Engine/Runtime/Requirements/PlaceAlongSpaceEdges.cs

@@ -9,22 +9,15 @@ namespace EscapeRoomEngine.Engine.Runtime.Requirements
     {
         protected override List<Placement> FilterCandidates(List<Placement> candidates, Module module, Space space)
         {
-            var right = space.rrPlacement.size.x - 1;
+            var sizeMinusOne = space.rrPlacement.size - Vector2Int.one;
-            var top = space.rrPlacement.size.y - 1;
             
             candidates.RemoveAll(candidate =>
             {
-                var keep = false;
+                var (left, right) = candidate.BackCorners;
-                        
+                return !(left.x == 0 && right.x == 0 ||
-                candidate.ForEachPosition(position =>
+                       left.z == 0 && right.z == 0 ||
-                {
+                       left.x == sizeMinusOne.x && right.x == sizeMinusOne.x ||
-                    if (!keep)
+                       left.z == sizeMinusOne.y && right.z == sizeMinusOne.y);
-                    {
-                        keep = position.x == 0 || position.x == right || position.z == 0 || position.z == top;
-                    }
-                });
-                        
-                return !keep;
             });
 
             return candidates;