variants/Chakart/class.js

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