+ isAttackedByLancer([x, y], color) {
+ for (let step of V.steps[V.ROOK].concat(V.steps[V.BISHOP])) {
+ // If in this direction there are only enemy pieces and empty squares,
+ // and we meet a lancer: can he reach us?
+ // NOTE: do not stop at first lancer, there might be several!
+ let coord = { x: x + step[0], y: y + step[1] };
+ let lancerPos = [];
+ while (
+ V.OnBoard(coord.x, coord.y) &&
+ (
+ this.board[coord.x][coord.y] == V.EMPTY ||
+ this.getColor(coord.x, coord.y) == color
+ )
+ ) {
+ if (
+ this.getPiece(coord.x, coord.y) == V.LANCER &&
+ !this.isImmobilized([coord.x, coord.y])
+ ) {
+ lancerPos.push({x: coord.x, y: coord.y});
+ }
+ coord.x += step[0];
+ coord.y += step[1];
+ }
+ const L = this.sentryPush.length;
+ const pl = (!!this.sentryPush[L-1] ? this.sentryPush[L-1].length : 0);
+ for (let xy of lancerPos) {
+ const dir = V.LANCER_DIRS[this.board[xy.x][xy.y].charAt(1)];
+ if (
+ (dir[0] == -step[0] && dir[1] == -step[1]) ||
+ // If the lancer was just pushed, this is an attack too:
+ (
+ !!this.sentryPush[L-1] &&
+ this.sentryPush[L-1][pl-1].x == xy.x &&
+ this.sentryPush[L-1][pl-1].y == xy.y
+ )
+ ) {
+ return true;
+ }
+ }
+ }
+ return false;
+ }
+
+ // Helper to check sentries attacks:
+ selfAttack([x1, y1], [x2, y2]) {
+ const color = this.getColor(x1, y1);
+ const oppCol = V.GetOppCol(color);
+ const sliderAttack = (allowedSteps, lancer) => {
+ const deltaX = x2 - x1,
+ deltaY = y2 - y1;
+ const absDeltaX = Math.abs(deltaX),
+ absDeltaY = Math.abs(deltaY);
+ const step = [ deltaX / absDeltaX || 0, deltaY / absDeltaY || 0 ];
+ if (
+ // Check that the step is a priori valid:
+ (absDeltaX != absDeltaY && deltaX != 0 && deltaY != 0) ||
+ allowedSteps.every(st => st[0] != step[0] || st[1] != step[1])
+ ) {
+ return false;
+ }
+ let sq = [ x1 + step[0], y1 + step[1] ];
+ while (sq[0] != x2 || sq[1] != y2) {
+ // NOTE: no need to check OnBoard in this special case
+ if (this.board[sq[0]][sq[1]] != V.EMPTY) {
+ const p = this.getPiece(sq[0], sq[1]);
+ const pc = this.getColor(sq[0], sq[1]);
+ if (
+ // Enemy sentry on the way will be gone:
+ (p != V.SENTRY || pc != oppCol) &&
+ // Lancer temporarily "changed color":
+ (!lancer || pc == color)
+ ) {
+ return false;
+ }
+ }
+ sq[0] += step[0];
+ sq[1] += step[1];
+ }
+ return true;
+ };
+ switch (this.getPiece(x1, y1)) {
+ case V.PAWN: {
+ // Pushed pawns move as enemy pawns
+ const shift = (color == 'w' ? 1 : -1);
+ return (x1 + shift == x2 && Math.abs(y1 - y2) == 1);
+ }
+ case V.KNIGHT: {
+ const deltaX = Math.abs(x1 - x2);
+ const deltaY = Math.abs(y1 - y2);
+ return (
+ deltaX + deltaY == 3 &&
+ [1, 2].includes(deltaX) &&
+ [1, 2].includes(deltaY)
+ );
+ }
+ case V.ROOK:
+ return sliderAttack(V.steps[V.ROOK]);
+ case V.BISHOP:
+ return sliderAttack(V.steps[V.BISHOP]);
+ case V.QUEEN:
+ return sliderAttack(V.steps[V.ROOK].concat(V.steps[V.BISHOP]));
+ case V.LANCER: {
+ // Special case: as long as no enemy units stands in-between,
+ // it attacks (if it points toward the king).
+ const allowedStep = V.LANCER_DIRS[this.board[x1][y1].charAt(1)];
+ return sliderAttack([allowedStep], "lancer");