variants/Chakart/class.js

   1 import ChessRules from "/base_rules.js";
   2 import {ArrayFun} from "/utils/array.js";
   3 import {Random} from "/utils/alea.js";
   4 import {FenUtil} from "/utils/setupPieces.js";
   5 import PiPo from "/utils/PiPo.js";
   6 import Move from "/utils/Move.js";
   7
   8 export default class ChakartRules extends ChessRules {
   9
  10   static get Options() {
  11     return {
  12       select: [
  13         {
  14           label: "Randomness",
  15           variable: "randomness",
  16           defaut: 2,
  17           options: [
  18             {label: "Deterministic", value: 0},
  19             {label: "Symmetric random", value: 1},
  20             {label: "Asymmetric random", value: 2}
  21           ]
  22         }
  23       ],
  24       styles: ["cylinder"]
  25     };
  26   }
  27
  28   get pawnPromotions() {
  29     return ['q', 'r', 'n', 'b', 'k'];
  30   }
  31
  32   get hasCastle() {
  33     return false;
  34   }
  35   get hasEnpassant() {
  36     return false;
  37   }
  38   get hasReserve() {
  39     return true;
  40   }
  41   get hasReserveFen() {
  42     return false;
  43   }
  44
  45   static get IMMOBILIZE_CODE() {
  46     return {
  47       'p': 's',
  48       'r': 'u',
  49       'n': 'o',
  50       'b': 'c',
  51       'q': 't',
  52       'k': 'l'
  53     };
  54   }
  55
  56   static get IMMOBILIZE_DECODE() {
  57     return {
  58       's': 'p',
  59       'u': 'r',
  60       'o': 'n',
  61       'c': 'b',
  62       't': 'q',
  63       'l': 'k'
  64     };
  65   }
  66
  67   // Fictive color 'a', bomb banana mushroom egg
  68   static get BOMB() {
  69     return 'w'; //"Wario"
  70   }
  71   static get BANANA() {
  72     return 'd'; //"Donkey"
  73   }
  74   static get EGG() {
  75     return 'e';
  76   }
  77   static get MUSHROOM() {
  78     return 'm';
  79   }
  80
  81   static get EGG_SURPRISE() {
  82     return [
  83       "kingboo", "bowser", "daisy", "koopa",
  84       "luigi", "waluigi", "toadette", "chomp"];
  85   }
  86
  87   canIplay(x, y) {
  88     if (
  89       this.playerColor != this.turn ||
  90       Object.keys(V.IMMOBILIZE_DECODE).includes(this.getPiece(x, y))
  91     ) {
  92       return false;
  93     }
  94     return this.egg == "kingboo" || this.getColor(x, y) == this.turn;
  95   }
  96
  97   pieces(color, x, y) {
  98     const specials = {
  99       'i': {"class": "invisible"}, //queen
 100       '?': {"class": "mystery"}, //...initial square
 101       'e': {"class": "egg"},
 102       'm': {"class": "mushroom"},
 103       'd': {"class": "banana"},
 104       'w': {"class": "bomb"},
 105       'z': {"class": "remote-capture"}
 106     };
 107     const bowsered = {
 108       's': {"class": ["immobilized", "pawn"]},
 109       'u': {"class": ["immobilized", "rook"]},
 110       'o': {"class": ["immobilized", "knight"]},
 111       'c': {"class": ["immobilized", "bishop"]},
 112       't': {"class": ["immobilized", "queen"]},
 113       'l': {"class": ["immobilized", "king"]}
 114     };
 115     return Object.assign(
 116       {
 117         'y': {
 118           // Virtual piece for "king remote shell captures"
 119           attack: [
 120             {
 121               steps: [
 122                 [0, 1], [0, -1], [1, 0], [-1, 0],
 123                 [1, 1], [1, -1], [-1, 1], [-1, -1]
 124               ]
 125             }
 126           ]
 127         }
 128       },
 129       specials, bowsered, super.pieces(color, x, y)
 130     );
 131   }
 132
 133   genRandInitBaseFen() {
 134     const s = FenUtil.setupPieces(
 135       ['r', 'n', 'b', 'q', 'k', 'b', 'n', 'r'],
 136       {
 137         randomness: this.options["randomness"],
 138         diffCol: ['b']
 139       }
 140     );
 141     return {
 142       fen: s.b.join("") + "/pppppppp/8/8/8/8/PPPPPPPP/" +
 143            s.w.join("").toUpperCase(),
 144       o: {flags: "1111"} //Peach + Mario
 145     };
 146   }
 147
 148   fen2board(f) {
 149     return (
 150       f.charCodeAt() <= 90
 151         ? "w" + f.toLowerCase()
 152         : (['w', 'd', 'e', 'm'].includes(f) ? "a" : "b") + f
 153     );
 154   }
 155
 156   setFlags(fenflags) {
 157     // King can send shell? Queen can be invisible?
 158     this.powerFlags = {
 159       w: {k: false, q: false},
 160       b: {k: false, q: false}
 161     };
 162     for (let c of ['w', 'b']) {
 163       for (let p of ['k', 'q']) {
 164         this.powerFlags[c][p] =
 165           fenflags.charAt((c == "w" ? 0 : 2) + (p == 'k' ? 0 : 1)) == "1";
 166       }
 167     }
 168   }
 169
 170   aggregateFlags() {
 171     return this.powerFlags;
 172   }
 173
 174   disaggregateFlags(flags) {
 175     this.powerFlags = flags;
 176   }
 177
 178   getFlagsFen() {
 179     return ['w', 'b'].map(c => {
 180       return ['k', 'q'].map(p => this.powerFlags[c][p] ? "1" : "0").join("");
 181     }).join("");
 182   }
 183
 184   setOtherVariables(fenParsed) {
 185     super.setOtherVariables(fenParsed);
 186     this.egg = null;
 187     // Change seed (after FEN generation!!)
 188     // so that further calls differ between players:
 189     Random.setSeed(Math.floor(19840 * Math.random()));
 190   }
 191
 192   initReserves() {
 193     this.reserve = {}; //to be filled later
 194   }
 195
 196   canStepOver(i, j) {
 197     return (
 198       this.board[i][j] == "" ||
 199       ['i', V.EGG, V.MUSHROOM].includes(this.getPiece(i, j))
 200     );
 201   }
 202
 203   // For Toadette bonus
 204   canDrop([c, p], [i, j]) {
 205     return (
 206       (
 207         this.board[i][j] == "" ||
 208         this.getColor(i, j) == 'a' ||
 209         this.getPiece(i, j) == 'i'
 210       )
 211       &&
 212       (p != "p" || (c == 'w' && i < this.size.x - 1) || (c == 'b' && i > 0))
 213     );
 214   }
 215
 216   getPotentialMovesFrom([x, y]) {
 217     let moves = [];
 218     const piece = this.getPiece(x, y);
 219     if (this.egg == "toadette")
 220       moves = this.getDropMovesFrom([x, y]);
 221     else if (this.egg == "kingboo") {
 222       const color = this.turn;
 223       const oppCol = C.GetOppCol(color);
 224       // Only allow to swap (non-immobilized!) pieces
 225       for (let i=0; i<this.size.x; i++) {
 226         for (let j=0; j<this.size.y; j++) {
 227           const colIJ = this.getColor(i, j);
 228           const pieceIJ = this.getPiece(i, j);
 229           if (
 230             (i != x || j != y) &&
 231             ['w', 'b'].includes(colIJ) &&
 232             !Object.keys(V.IMMOBILIZE_DECODE).includes(pieceIJ) &&
 233             // Next conditions = no pawn on last rank
 234             (
 235               piece != 'p' ||
 236               (
 237                 (color != 'w' || i != 0) &&
 238                 (color != 'b' || i != this.size.x - 1)
 239               )
 240             )
 241             &&
 242             (
 243               pieceIJ != 'p' ||
 244               (
 245                 (colIJ != 'w' || x != 0) &&
 246                 (colIJ != 'b' || x != this.size.x - 1)
 247               )
 248             )
 249           ) {
 250             let m = this.getBasicMove([x, y], [i, j]);
 251             m.appear.push(new PiPo({x: x, y: y, p: pieceIJ, c: colIJ}));
 252             m.kingboo = true; //avoid some side effects (bananas/bombs)
 253             moves.push(m);
 254           }
 255         }
 256       }
 257     }
 258     else {
 259       // Normal case (including bonus daisy)
 260       switch (piece) {
 261         case 'p':
 262           moves = this.getPawnMovesFrom([x, y]); //apply promotions
 263           break;
 264         case 'q':
 265           moves = this.getQueenMovesFrom([x, y]);
 266           break;
 267         case 'k':
 268           moves = this.getKingMovesFrom([x, y]);
 269           break;
 270         case 'n':
 271           moves = this.getKnightMovesFrom([x, y]);
 272           break;
 273         case 'b':
 274         case 'r':
 275           // Explicitely listing types to avoid moving immobilized piece
 276           moves = super.getPotentialMovesOf(piece, [x, y]);
 277           break;
 278       }
 279     }
 280     return moves;
 281   }
 282
 283   getPawnMovesFrom([x, y]) {
 284     const color = this.turn;
 285     const oppCol = C.GetOppCol(color);
 286     const shiftX = (color == 'w' ? -1 : 1);
 287     const firstRank = (color == "w" ? this.size.x - 1 : 0);
 288     let moves = [];
 289     const frontPiece = this.getPiece(x + shiftX, y);
 290     if (
 291       this.board[x + shiftX][y] == "" ||
 292       this.getColor(x + shiftX, y) == 'a' ||
 293       frontPiece == 'i'
 294     ) {
 295       moves.push(this.getBasicMove([x, y], [x + shiftX, y]));
 296       if (
 297         [firstRank, firstRank + shiftX].includes(x) &&
 298         ![V.BANANA, V.BOMB].includes(frontPiece) &&
 299         (
 300           this.board[x + 2 * shiftX][y] == "" ||
 301           this.getColor(x + 2 * shiftX, y) == 'a' ||
 302           this.getPiece(x + 2 * shiftX, y) == 'i'
 303         )
 304       ) {
 305         moves.push(this.getBasicMove([x, y], [x + 2 * shiftX, y]));
 306       }
 307     }
 308     for (let shiftY of [-1, 1]) {
 309       const nextY = this.getY(y + shiftY);
 310       if (
 311         nextY >= 0 &&
 312         nextY < this.size.y &&
 313         this.board[x + shiftX][nextY] != "" &&
 314         // Pawns cannot capture invisible queen this way!
 315         this.getPiece(x + shiftX, nextY) != 'i' &&
 316         ['a', oppCol].includes(this.getColor(x + shiftX, nextY))
 317       ) {
 318         moves.push(this.getBasicMove([x, y], [x + shiftX, nextY]));
 319       }
 320     }
 321     moves = super.pawnPostProcess(moves, color, oppCol);
 322     // Add mushroom on before-last square (+ potential segments)
 323     moves.forEach(m => {
 324       let [mx, my] = [x, y];
 325       if (Math.abs(m.end.x - m.start.x) == 2)
 326         mx = (m.start.x + m.end.x) / 2;
 327       m.appear.push(new PiPo({x: mx, y: my, c: 'a', p: 'm'}));
 328       if (mx != x && this.board[mx][my] != "") {
 329         m.vanish.push(new PiPo({
 330           x: mx,
 331           y: my,
 332           c: this.getColor(mx, my),
 333           p: this.getPiece(mx, my)
 334         }));
 335       }
 336       if (Math.abs(m.end.y - m.start.y) > 1) {
 337         m.segments = [
 338           [[x, y], [x, y]],
 339           [[m.end.x, m.end.y], [m.end.x, m.end.y]]
 340         ];
 341       }
 342     });
 343     return moves;
 344   }
 345
 346   getKnightMovesFrom([x, y]) {
 347     // Add egg on initial square:
 348     return super.getPotentialMovesOf('n', [x, y]).map(m => {
 349       m.appear.push(new PiPo({p: "e", c: "a", x: x, y: y}));
 350       return m;
 351     });
 352   }
 353
 354   getQueenMovesFrom(sq) {
 355     const normalMoves = super.getPotentialMovesOf('q', sq);
 356     // If flag allows it, add 'invisible movements'
 357     let invisibleMoves = [];
 358     if (this.powerFlags[this.turn]['q']) {
 359       normalMoves.forEach(m => {
 360         if (
 361           m.appear.length == 1 &&
 362           m.vanish.length == 1 &&
 363           // Only simple non-capturing moves:
 364           m.vanish[0].c != 'a'
 365         ) {
 366           let im = JSON.parse(JSON.stringify(m));
 367           im.appear[0].p = 'i';
 368           im.noAnimate = true;
 369           invisibleMoves.push(im);
 370         }
 371       });
 372     }
 373     return normalMoves.concat(invisibleMoves);
 374   }
 375
 376   getKingMovesFrom([x, y]) {
 377     let moves = super.getPotentialMovesOf('k', [x, y]);
 378     // If flag allows it, add 'remote shell captures'
 379     if (this.powerFlags[this.turn]['k']) {
 380       let shellCaptures = super.getPotentialMovesOf('y', [x, y]);
 381       shellCaptures.forEach(sc => {
 382         sc.shell = true; //easier play()
 383         sc.choice = 'z'; //to display in showChoices()
 384         // Fix move (Rifle style):
 385         sc.vanish.shift();
 386         sc.appear.shift();
 387       });
 388       Array.prototype.push.apply(moves, shellCaptures);
 389     }
 390     return moves;
 391   }
 392
 393   play(move) {
 394     const color = this.turn;
 395     const oppCol = C.GetOppCol(color);
 396     this.egg = move.egg;
 397     if (move.egg == "toadette") {
 398       this.reserve = { w: {}, b: {} };
 399       // Randomly select a piece in pawnPromotions
 400       if (!move.toadette)
 401         move.toadette = Random.sample(this.pawnPromotions);
 402       this.reserve[color][move.toadette] = 1;
 403       this.re_drawReserve([color]);
 404     }
 405     else if (Object.keys(this.reserve).length > 0) {
 406       this.reserve = {};
 407       this.re_drawReserve([color]);
 408     }
 409     if (move.shell)
 410       this.powerFlags[color]['k'] = false;
 411     else if (move.appear.length > 0 && move.appear[0].p == 'i') {
 412       this.powerFlags[move.appear[0].c]['q'] = false;
 413       if (color == this.playerColor) {
 414         move.appear.push(
 415           new PiPo({x: move.start.x, y: move.start.y, c: color, p: '?'}));
 416       }
 417     }
 418     if (color == this.playerColor) {
 419       // Look for an immobilized piece of my color: it can now move
 420       for (let i=0; i<8; i++) {
 421         for (let j=0; j<8; j++) {
 422           if ((i != move.end.x || j != move.end.y) && this.board[i][j] != "") {
 423             const piece = this.getPiece(i, j);
 424             if (
 425               this.getColor(i, j) == color &&
 426               Object.keys(V.IMMOBILIZE_DECODE).includes(piece)
 427             ) {
 428               move.vanish.push(new PiPo({
 429                 x: i, y: j, c: color, p: piece
 430               }));
 431               move.appear.push(new PiPo({
 432                 x: i, y: j, c: color, p: V.IMMOBILIZE_DECODE[piece]
 433               }));
 434             }
 435           }
 436         }
 437       }
 438       // Also make opponent invisible queen visible again, if any
 439       for (let i=0; i<8; i++) {
 440         for (let j=0; j<8; j++) {
 441           if (
 442             this.board[i][j] != "" &&
 443             this.getColor(i, j) == oppCol
 444           ) {
 445             const pieceIJ = this.getPiece(i, j);
 446             if (
 447               pieceIJ == 'i' &&
 448               // Ensure that current move doesn't erase invisible queen
 449               move.appear.every(a => a.x != i || a.y != j)
 450             ) {
 451               move.vanish.push(new PiPo({x: i, y: j, c: oppCol, p: 'i'}));
 452               move.appear.push(new PiPo({x: i, y: j, c: oppCol, p: 'q'}));
 453             }
 454             else if (pieceIJ == '?')
 455               move.vanish.push(new PiPo({x: i, y: j, c: oppCol, p: '?'}));
 456           }
 457         }
 458       }
 459     }
 460     this.playOnBoard(move);
 461     super.postPlay(move);
 462   }
 463
 464   playVisual(move, r) {
 465     super.playVisual(move, r);
 466     if (move.egg)
 467       this.displayBonus(move);
 468   }
 469
 470   buildMoveStack(move, r) {
 471     const color = this.turn;
 472     if (
 473       move.appear.length > 0 &&
 474       move.appear[0].p == 'p' &&
 475       (
 476         (color == 'w' && move.end.x == 0) ||
 477         (color == 'b' && move.end.x == this.size.x - 1)
 478       )
 479     ) {
 480       // "Forgotten" promotion, which occurred after some effect
 481       let moves = super.pawnPostProcess([move], color, C.GetOppCol(color));
 482       super.showChoices(moves, r);
 483     }
 484     else
 485       super.buildMoveStack(move, r);
 486   }
 487
 488   computeNextMove(move) {
 489     if (move.koopa)
 490       return null;
 491     // Set potential random effects, so that play() is deterministic
 492     // from opponent viewpoint:
 493     const endPiece = this.getPiece(move.end.x, move.end.y);
 494     switch (endPiece) {
 495       case V.EGG:
 496         move.egg = Random.sample(V.EGG_SURPRISE);
 497         move.next = this.getEggEffect(move);
 498         break;
 499       case V.MUSHROOM:
 500         move.next = this.getMushroomEffect(move);
 501         break;
 502       case V.BANANA:
 503       case V.BOMB:
 504         move.next = this.getBombBananaEffect(move, endPiece);
 505         break;
 506     }
 507     // NOTE: Chakart has also some side-effects:
 508     if (
 509       !move.next && move.appear.length > 0 &&
 510       !move.kingboo && !move.luigiEffect
 511     ) {
 512       const movingPiece = move.appear[0].p;
 513       if (['b', 'r'].includes(movingPiece)) {
 514         // Drop a banana or bomb:
 515         const bs =
 516           this.getRandomSquare([move.end.x, move.end.y],
 517             movingPiece == 'r'
 518               ? [[1, 1], [1, -1], [-1, 1], [-1, -1]]
 519               : [[1, 0], [-1, 0], [0, 1], [0, -1]],
 520             "freeSquare");
 521         if (bs) {
 522           move.appear.push(
 523             new PiPo({
 524               x: bs[0],
 525               y: bs[1],
 526               c: 'a',
 527               p: movingPiece == 'r' ? 'd' : 'w'
 528             })
 529           );
 530           if (this.board[bs[0]][bs[1]] != "") {
 531             move.vanish.push(
 532               new PiPo({
 533                 x: bs[0],
 534                 y: bs[1],
 535                 c: this.getColor(bs[0], bs[1]),
 536                 p: this.getPiece(bs[0], bs[1])
 537               })
 538             );
 539           }
 540         }
 541       }
 542     }
 543   }
 544
 545   isLastMove(move) {
 546     return !move.next && !["daisy", "toadette", "kingboo"].includes(move.egg);
 547   }
 548
 549   // Helper to set and apply banana/bomb effect
 550   getRandomSquare([x, y], steps, freeSquare) {
 551     let validSteps = steps.filter(s => this.onBoard(x + s[0], y + s[1]));
 552     if (freeSquare) {
 553       // Square to put banana/bomb cannot be occupied by a piece
 554       validSteps = validSteps.filter(s => {
 555         return ["", 'a'].includes(this.getColor(x + s[0], y + s[1]))
 556       });
 557     }
 558     if (validSteps.length == 0)
 559       return null;
 560     const step = validSteps[Random.randInt(validSteps.length)];
 561     return [x + step[0], y + step[1]];
 562   }
 563
 564   getEggEffect(move) {
 565     const getRandomPiece = (c) => {
 566       let bagOfPieces = [];
 567       for (let i=0; i<this.size.x; i++) {
 568         for (let j=0; j<this.size.y; j++) {
 569           const pieceIJ = this.getPiece(i, j);
 570           if (
 571             this.getColor(i, j) == c && pieceIJ != 'k' &&
 572             (
 573               // The color will change, so pawns on first rank are ineligible
 574               pieceIJ != 'p' ||
 575               (c == 'w' && i < this.size.x - 1) || (c == 'b' && i > 0)
 576             )
 577           ) {
 578             bagOfPieces.push([i, j]);
 579           }
 580         }
 581       }
 582       if (bagOfPieces.length >= 1)
 583         return Random.sample(bagOfPieces);
 584       return null;
 585     };
 586     const color = this.turn;
 587     let em = null;
 588     switch (move.egg) {
 589       case "luigi":
 590       case "waluigi":
 591         // Change color of friendly or enemy piece, king excepted
 592         const oldColor = (move.egg == "waluigi" ? color : C.GetOppCol(color));
 593         const newColor = C.GetOppCol(oldColor);
 594         const coords = getRandomPiece(oldColor);
 595         if (coords) {
 596           const piece = this.getPiece(coords[0], coords[1]);
 597           em = new Move({
 598             appear: [
 599               new PiPo({x: coords[0], y: coords[1], c: newColor, p: piece})
 600             ],
 601             vanish: [
 602               new PiPo({x: coords[0], y: coords[1], c: oldColor, p: piece})
 603             ]
 604           });
 605           em.luigiEffect = true; //avoid dropping bomb/banana by mistake
 606         }
 607         break;
 608       case "bowser":
 609         em = new Move({
 610           appear: [
 611             new PiPo({
 612               x: move.end.x,
 613               y: move.end.y,
 614               c: color,
 615               p: V.IMMOBILIZE_CODE[move.appear[0].p]
 616             })
 617           ],
 618           vanish: [
 619             new PiPo({
 620               x: move.end.x,
 621               y: move.end.y,
 622               c: color,
 623               p: move.appear[0].p
 624             })
 625           ]
 626         });
 627         break;
 628       case "koopa":
 629         // Reverse move
 630         em = new Move({
 631           appear: [
 632             new PiPo({
 633               x: move.start.x, y: move.start.y, c: color, p: move.appear[0].p
 634             })
 635           ],
 636           vanish: [
 637             new PiPo({
 638               x: move.end.x, y: move.end.y, c: color, p: move.appear[0].p
 639             })
 640           ]
 641         });
 642         if (this.board[move.start.x][move.start.y] != "") {
 643           // Pawn or knight let something on init square
 644           em.vanish.push(new PiPo({
 645             x: move.start.x,
 646             y: move.start.y,
 647             c: 'a',
 648             p: this.getPiece(move.start.x, move.start.y)
 649           }));
 650         }
 651         em.koopa = true; //avoid applying effect
 652         break;
 653       case "chomp":
 654         // Eat piece
 655         em = new Move({
 656           appear: [],
 657           vanish: [
 658             new PiPo({
 659               x: move.end.x, y: move.end.y, c: color, p: move.appear[0].p
 660             })
 661           ],
 662           end: {x: move.end.x, y: move.end.y}
 663         });
 664         break;
 665     }
 666     if (em && move.egg != "koopa")
 667       em.noAnimate = true; //static move
 668     return em;
 669   }
 670
 671   getMushroomEffect(move) {
 672     if (
 673       typeof move.start.x == "string" || //drop move (toadette)
 674       ['b', 'r', 'q'].includes(move.vanish[0].p) //slider
 675     ) {
 676       return null;
 677     }
 678     let step = [move.end.x - move.start.x, move.end.y - move.start.y];
 679     if (Math.abs(step[0]) == 2 && Math.abs(step[1]) == 0)
 680       // Pawn initial 2-squares move: normalize step
 681       step[0] /= 2;
 682     const nextSquare = [move.end.x + step[0], move.end.y + step[1]];
 683     let nextMove = null;
 684     if (
 685       this.onBoard(nextSquare[0], nextSquare[1]) &&
 686       (
 687         this.board[nextSquare[0]][nextSquare[1]] == "" ||
 688         this.getColor(nextSquare[0], nextSquare[1]) == 'a'
 689       )
 690     ) {
 691       this.playOnBoard(move); //HACK for getBasicMove()
 692       nextMove = this.getBasicMove([move.end.x, move.end.y], nextSquare);
 693       this.undoOnBoard(move);
 694     }
 695     return nextMove;
 696   }
 697
 698   getBombBananaEffect(move, item) {
 699     const steps = item == V.BANANA
 700       ? [[1, 0], [-1, 0], [0, 1], [0, -1]]
 701       : [[1, 1], [1, -1], [-1, 1], [-1, -1]];
 702     const nextSquare = this.getRandomSquare([move.end.x, move.end.y], steps);
 703     this.playOnBoard(move); //HACK for getBasicMove()
 704     const res = this.getBasicMove([move.end.x, move.end.y], nextSquare);
 705     this.undoOnBoard(move);
 706     return res;
 707   }
 708
 709   displayBonus(move) {
 710     super.displayMessage(null, move.egg, "bonus-text", 2000);
 711   }
 712
 713   atLeastOneMove() {
 714     return true;
 715   }
 716
 717   filterValid(moves) {
 718     return moves;
 719   }
 720
 721   // Kingboo bonus can be animated better:
 722   customAnimate(move, segments, cb) {
 723     if (!move.kingboo)
 724       return 0;
 725     super.animateMoving(move.end, move.start, null,
 726                         segments.reverse().map(s => s.reverse()), cb);
 727     return 1;
 728   }
 729
 730 };