h

chess/src/chess/Board.java

@@ -10,6 +10,7 @@ import javalib.worldimages.EmptyImage;
 import javalib.worldimages.OutlineMode;
 import javalib.worldimages.OverlayImage;
 import javalib.worldimages.RectangleImage;
+import javalib.worldimages.TextImage;
 import javalib.worldimages.WorldImage;
 
 class Board {
@@ -46,6 +47,8 @@ class Board {
                         Util.scale, Util.scale, OutlineMode.SOLID,
                         new Color(200, 50, 200, 150)
                     );
+                else if (info == Info.CHECK)
+                    infoImage = new TextImage("!", Util.scale, Color.RED);
 
                 scene.placeImageXY(
                     new OverlayImage(
@@ -136,6 +139,13 @@ class Board {
         }
 
         this.game.changeActive();
+
+        // Check if in check after last move.
+        if (this.inCheck()) {
+            this.info.put(this.activeKing(), Info.CHECK);
+        } else {
+            this.info.remove(this.activeKing());
+        }
     }
 
     // Get the valid moves for a piece.
@@ -196,6 +206,18 @@ class Board {
         return false;
     }
 
+    // Get the coords of the active actor's king.
+    Coord activeKing() {
+        for (Map.Entry<Coord, Piece> entry : this.board.entrySet()) {
+            Piece piece = entry.getValue();
+            if (piece != null && piece.type == PieceType.KING &&
+                piece.col == this.game.activeActor.col) {
+                return entry.getKey();
+            }
+        }
+        return null;
+    }
+
     // Return the line of free spaces above.
     ArrayList<Coord> getLineAbove(Coord coord, Util.Col col) {
         ArrayList<Coord> line = new ArrayList<>();
@@ -286,10 +308,40 @@ class Board {
         }
         return line;
     }
+
+    // Return all the posible move locations of a color.
+    ArrayList<Coord> allMoves(Util.Col col) {
+        ArrayList<Coord> moves = new ArrayList<>();
+        for (int x = 0; x < Util.boardW; x++)
+            for (int y = 0; y < Util.boardW; y++) {
+                Coord coord = new Coord(x, y);
+                Piece piece = this.get(coord);
+                if (piece != null && piece.col.equals(col))
+                    moves.addAll(piece.moves(coord, this));
+            }
+
+        return moves;
+    }
+
+    // Check if list of coords contains the king (check).
+    boolean check(ArrayList<Coord> coords) {
+        for (Coord coord : coords) {
+            Piece piece = this.get(coord);
+            if (piece != null && piece.type.equals(PieceType.KING)) return true;
+        }
+        return false;
+    }
+
+    // Check if active actor is in check.
+    boolean inCheck() {
+        ArrayList<Coord> allEnemyMoves =
+            allMoves(Util.reverse(this.game.activeActor.col));
+        return check(allEnemyMoves);
+    }
 }
 
 // Information layered over the board.
-enum Info { CANMOVE, WARN, SELECTED, PROMOTION }
+enum Info { CANMOVE, WARN, SELECTED, PROMOTION, CHECK }
 
 // Measured from top left.
 class Coord {

chess/src/chess/Util.java

@@ -16,4 +16,7 @@ class Util {
 
     // The color a piece can be.
     enum Col { WHITE, BLACK }
+    static Col reverse(Col col) {
+        return col == Col.WHITE ? Col.BLACK : Col.WHITE;
+    }
 }