46 lines
1.7 KiB
Plaintext
46 lines
1.7 KiB
Plaintext
/* helper – robust coord access */
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function cx(c) { return c.x ?? c[0] }
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function cy(c) { return c.y ?? c[1] }
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/* simple move-shape checks */
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var deltas = {
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pawn: function (pc, dx, dy, grid, to) {
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var dir = (pc.colour == 'white') ? -1 : 1;
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var base = (pc.colour == 'white') ? 6 : 1;
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var one = (dy == dir && dx == 0 && grid.at(to).length == 0);
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var two = (dy == 2 * dir && dx == 0 && cy(pc.coord) == base &&
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grid.at({ x: cx(pc.coord), y: cy(pc.coord)+dir }).length == 0 &&
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grid.at(to).length == 0);
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var cap = (dy == dir && Math.abs(dx) == 1 && grid.at(to).length);
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return one || two || cap;
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},
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rook : function (pc, dx, dy) { return (dx == 0 || dy == 0); },
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bishop: function (pc, dx, dy) { return Math.abs(dx) == Math.abs(dy); },
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queen : function (pc, dx, dy) { return (dx == 0 || dy == 0 || Math.abs(dx) == Math.abs(dy)); },
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knight: function (pc, dx, dy) { return (Math.abs(dx) == 1 && Math.abs(dy) == 2) ||
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(Math.abs(dx) == 2 && Math.abs(dy) == 1); },
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king : function (pc, dx, dy) { return Math.max(Math.abs(dx), Math.abs(dy)) == 1; }
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};
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function clearLine(from, to, grid) {
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var dx = Math.sign(cx(to) - cx(from));
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var dy = Math.sign(cy(to) - cy(from));
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var x = cx(from) + dx, y = cy(from) + dy;
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while (x != cx(to) || y != cy(to)) {
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if (grid.at({ x: x, y: y }).length) return false;
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x += dx; y += dy;
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}
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return true;
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}
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function canMove(piece, from, to, grid) {
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var dx = cx(to) - cx(from);
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var dy = cy(to) - cy(from);
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var f = deltas[piece.kind];
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if (!f || !f(piece, dx, dy, grid, to)) return false;
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if (piece.kind == 'knight') return true;
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return clearLine(from, to, grid);
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}
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return { canMove };
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