Question

I have a 2D array containing all the Piece objects, each an instance of Rook, Bishop, King etc…

How can I find out if the path from srcX,srcY to dstX,dstY is obstructed by another piece?

The only things I can think of would involve massive amounts of tedious code =/

Answer 1

Your comment about "massive amounts of tedious code" is a huge exaggeration. No path on a chessboard is more than eight squares, and all of them can be followed by a simple algorithm – incrementing or decrementing the row and/or column counter. (Except for the knight, which can only move to eight squares and can’t be blocked.) I doubt that the code for any piece takes longer than twenty lines.

For example here is the code for a bishop:

// check move legality not taking into account blocking
  boolean canMoveBishopTo(int srcx,int srcY,int destX,int destY) {
      if (srcX<0 || srcX>7 ||srcY<0 || srcY>7 || destX<0 || destX>7 ||destY<0 || destY>7) {
        throw new IllegalArgumentException();
      }
      if ((srcX==destX || srcY==destY) {
        return false;
      }

      if (Math.abs(destX-srcX) == Math.abs(srcY-destY) {
        return true;
      }
      return false;
    }

boolean isBishopMoveBlocked(int srcX,int srcY,int destX,int destY) {
  // assume we have already done the tests above
  int dirX = destX > srcX ? 1 : -1;
  int dirY = destY > srcY ? 1 : -1;
  for (int i=1; i < Math.abs(destX - srcX) - 1; ++i) {
    if (pieceOnSquare(srcX + i*dirX, srcY + i*dirY) {
      return false;
    }
  }
  return true;
}