chess/frontend/visuals.js

const BOX_SIDE = 80;
const INDEX_MARGIN = BOX_SIDE / 2;
const INDEX_LETTERS = "abcdefgh";

export class Canvas {
  constructor() {
    this._canvas = document.createElement("canvas");
    this._ctx = this._canvas.getContext("2d");
    let boardSide = BOX_SIDE * 8 + INDEX_MARGIN;
    this._canvas.width = boardSide;
    this._canvas.height = boardSide;
    document.body.appendChild(this._canvas);
    this.drawChessBoard();
  }
  decideColor(r, c) {
    if ((r + c) % 2) return "#c0c0c0";
    else return "#ffffff";
  }
  drawSquareColor(color, r, c) {
    const crtStyle = this._ctx.fillStyle;
    this._ctx.fillStyle = color;
    this._ctx.fillRect(
      c * BOX_SIDE + INDEX_MARGIN,
      r * BOX_SIDE + INDEX_MARGIN,
      BOX_SIDE,
      BOX_SIDE
    );
    this._ctx.fillStyle = crtStyle;
  }
  drawChessBoard() {
    // Draw squares
    for (let r = 0; r < 8; r++) {
      for (let c = 0; c < 8; c++) {
        this.drawSquareColor(this.decideColor(r, c), r, c);
      }
    }

    // Draw letters
    this._ctx.fillStyle = "black";
    let fontsize = INDEX_MARGIN / 2;
    this._ctx.font = `${fontsize}px Monospace`;
    for (let idx = 0; idx < 8; idx++) {
      this._ctx.fillText(
        INDEX_LETTERS[idx],
        BOX_SIDE * idx + BOX_SIDE / 2 + INDEX_MARGIN - fontsize / 4,
        INDEX_MARGIN / 2
      );
      this._ctx.fillText(
        (8 - idx).toString(),
        INDEX_MARGIN / 2 - fontsize / 4,
        BOX_SIDE * idx + BOX_SIDE / 2 + INDEX_MARGIN + fontsize / 4
      );
    }
  }
  screenCoordsToRowCol(cx, cy) {
    let canvasRect = this._canvas.getBoundingClientRect();
    if (cx > canvasRect.right || cy > canvasRect.bottom) {
      return null;
    }
    let canvasX = cx - canvasRect.left;
    let canvasY = cy - canvasRect.top;
    let row = Math.floor((canvasY - INDEX_MARGIN) / BOX_SIDE);
    let col = Math.floor((canvasX - INDEX_MARGIN) / BOX_SIDE);
    return [row, col];
  }
  rowColToScreenCoords(row, col) {
    let canvasRect = this._canvas.getBoundingClientRect();
    let topPx =
      canvasRect.top + INDEX_MARGIN + row * BOX_SIDE + window.pageYOffset;
    let leftPx =
      canvasRect.left + INDEX_MARGIN + col * BOX_SIDE + window.pageXOffset;
    return [topPx, leftPx];
  }
}

function boardIndexToRowCol(boardIndex) {
  let [colLetter, rowDigit] = boardIndex;
  let row = 8 - parseInt(rowDigit);
  let col = INDEX_LETTERS.indexOf(colLetter);
  return [row, col];
}

export function rowColToBoardIndex(row, col) {
  let rowDigit = 8 - row;
  let colLetter = INDEX_LETTERS[col];
  return `${colLetter}${rowDigit}`;
}

export class ActiveSquares {
  constructor() {
    this.selectedSquare = null;
  }
  selectSquare(canvas, position) {
    let [r, c] = boardIndexToRowCol(position);
    canvas.drawSquareColor("#c0c0ff", r, c);
    this.selectedSquare = position;
  }
  unselectSquare(canvas) {
    if (this.selectedSquare === null) return;
    let [r, c] = boardIndexToRowCol(this.selectedSquare);
    canvas.drawSquareColor(canvas.decideColor(r, c), r, c);
    this.selectedSquare = null;
  }
}

class PieceVis {
  constructor(piece) {
    this.piece = piece;
    this.im = null;
  }
  get ["icon"]() {
    return `./icons/${this.piece.piece_type}_${this.piece.color}.svg`;
  }
  draw(canvas, position) {
    let [topPx, leftPx] = canvas.rowColToScreenCoords(
      ...boardIndexToRowCol(position),
      canvas
    );
    if (this.im === null) {
      let im = new Image(BOX_SIDE, BOX_SIDE);
      im.src = this.icon;
      im.onload = () => {
        im.style.position = "absolute";
        im.style.top = `${topPx}px`;
        im.style.left = `${leftPx}px`;
      };
      document.body.appendChild(im);
      this.im = im;
    } else {
      this.im.style.top = `${topPx}px`;
      this.im.style.left = `${leftPx}px`;
    }
  }
  undraw() {
    if (this.im !== null) {
      this.im.remove();
      this.im = null;
    }
  }
}

export class ConfigVis {
  constructor(configuration) {
    this.configuration = configuration;
    this.piecesVis = new Map();
  }
  draw(canvas) {
    for (let [position, piece] of this.configuration.board) {
      if (this.piecesVis.has(position)) {
        if (this.piecesVis.get(position).piece == piece) {
          continue;
        }
      }
      let pv = this.piecesVis.get(position);
      if (pv !== undefined) {
        pv.undraw();
      }
      pv = new PieceVis(piece);
      pv.draw(canvas, position);
      this.piecesVis.set(position, pv);
    }
    for (let [position, pv] of this.piecesVis) {
      if (!this.configuration.board.has(position)) {
        pv.undraw();
        this.piecesVis.delete(position);
      }
    }
  }
  undraw() {
    for (let pv of this.piecesVis.values()) {
      pv.undraw();
    }
    this.piecesVis.clear();
  }
}