{
return 500; //checkmates evals may be slightly below 1000
}
+
+ // In this special situation, we just look 1 half move ahead
+ getComputerMove()
+ {
+ const maxeval = V.INFINITY;
+ const color = this.turn;
+ const oppCol = this.getOppCol(color);
+ const pawnShift = (color == "w" ? -1 : 1);
+ const kp = this.kingPos[color];
+
+ // Do not cheat: the current enlightment is all we can see
+ const myLight = JSON.parse(JSON.stringify(this.enlightened[color]));
+
+ // Can a slider on (i,j) apparently take my king?
+ // NOTE: inaccurate because assume yes if some squares are shadowed
+ const sliderTake = ([i,j], piece) => {
+ let step = undefined;
+ if (piece == V.BISHOP)
+ {
+ if (Math.abs(kp[0] - i) == Math.abs(kp[1] - j))
+ {
+ step =
+ [
+ (i-kp[0]) / Math.abs(i-kp[0]),
+ (j-kp[1]) / Math.abs(j-kp[1])
+ ];
+ }
+ }
+ else if (piece == V.ROOK)
+ {
+ if (kp[0] == i)
+ step = [0, (j-kp[1]) / Math.abs(j-kp[1])];
+ else if (kp[1] == j)
+ step = [(i-kp[0]) / Math.abs(i-kp[0]), 0];
+ }
+ if (!step)
+ return false;
+ // Check for obstacles
+ let obstacle = false;
+ for (
+ let x=kp[0]+step[0], y=kp[1]+step[1];
+ x != i && y != j;
+ x += step[0], y+= step[1])
+ {
+ if (myLight[x][y] && this.board[x][y] != V.EMPTY)
+ {
+ obstacle = true;
+ break;
+ }
+ }
+ if (!obstacle)
+ return true;
+ return false;
+ };
+
+ // Do I see something which can take my king ?
+ const kingThreats = () => {
+ for (let i=0; i<V.size.x; i++)
+ {
+ for (let j=0; j<V.size.y; j++)
+ {
+ if (myLight[i][j] && this.board[i][j] != V.EMPTY
+ && this.getColor(i,j) != color)
+ {
+ switch (this.getPiece(i,j))
+ {
+ case V.PAWN:
+ if (kp[0] + pawnShift == i && Math.abs(kp[1]-j) == 1)
+ return true;
+ break;
+ case V.KNIGHT:
+ if ((Math.abs(kp[0] - i) == 2 && Math.abs(kp[1] - j) == 1) ||
+ (Math.abs(kp[0] - i) == 1 && Math.abs(kp[1] - j) == 2))
+ {
+ return true;
+ }
+ break;
+ case V.KING:
+ if (Math.abs(kp[0] - i) == 1 && Math.abs(kp[1] - j) == 1)
+ return true;
+ break;
+ case V.BISHOP:
+ if (sliderTake([i,j], V.BISHOP))
+ return true;
+ break;
+ case V.ROOK:
+ if (sliderTake([i,j], V.ROOK))
+ return true;
+ break;
+ case V.QUEEN:
+ if (sliderTake([i,j], V.BISHOP) || sliderTake([i,j], V.ROOK))
+ return true;
+ break;
+ }
+ }
+ }
+ }
+ return false;
+ };
+
+ let moves = this.getAllValidMoves();
+ for (let move of moves)
+ {
+ this.play(move);
+ if (this.kingPos[oppCol][0] >= 0 && kingThreats())
+ {
+ // We didn't take opponent king, and our king will be captured: bad
+ move.eval = -maxeval;
+ }
+ this.undo(move);
+ if (!!move.eval)
+ continue;
+
+ move.eval = 0; //a priori...
+
+ // Can I take something ? If yes, do it if it seems good...
+ if (move.vanish.length == 2 && move.vanish[1].c != color) //avoid castle
+ {
+ const myPieceVal = V.VALUES[move.appear[0].p];
+ const hisPieceVal = V.VALUES[move.vanish[1].p];
+ if (myPieceVal <= hisPieceVal)
+ move.eval = hisPieceVal - myPieceVal + 2; //favor captures
+ else
+ {
+ // Taking a pawn with minor piece,
+ // or minor piece or pawn with a rook,
+ // or anything but a queen with a queen,
+ // or anything with a king.
+ // ==> Do it at random, although
+ // this is clearly inferior to what a human can deduce...
+ move.eval = (Math.random() < 0.5 ? 1 : -1);
+ }
+ }
+ }
+
+ // TODO: also need to implement the case when an opponent piece (in light)
+ // is threatening something - maybe not the king, but e.g. pawn takes rook.
+
+ moves.sort((a,b) => b.eval - a.eval);
+ let candidates = [0];
+ for (let j=1; j<moves.length && moves[j].eval == moves[0].eval; j++)
+ candidates.push(j);
+ return moves[_.sample(candidates, 1)];
+ }
}
const VariantRules = DarkRules;
projects / vchess.git / blobdiff