nes-emu/cartridge/Cartridge.js

A NES emulator

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = void 0;
var _mappers = _interopRequireDefault(require("./mappers"));
var _constants = _interopRequireDefault(require("../constants"));
var _helpers = require("../helpers");
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
/** The game cartridge (a file in iNES format). */
class Cartridge {
  constructor(bytes) {
    this.bytes = bytes;
    if (this.magicNumber !== _constants.default.ROM_MAGIC_NUMBER) throw new Error("Invalid ROM format.");
  }

  /** Returns a new instance of the right mapper. */
  createMapper() {
    const mapperId = this.header.mapperId;
    const Mapper = _mappers.default[mapperId];
    if (!Mapper) throw new Error("Unknown mapper: ".concat(mapperId, "."));
    return new Mapper();
  }

  /** Returns the PRG ROM, which contains the game's code. */
  get prgRom() {
    return this._getBytes(this._programOffset, this._programSize);
  }

  /** Returns the CHR ROM buffer (which contains static tilesets) or a CHR RAM buffer. */
  get chrRom() {
    const offset = this._programOffset + this._programSize;
    const size = this.header.chrRomPages * _constants.default.CHR_ROM_PAGE_SIZE;
    return !this.header.usesChrRam ? this._getBytes(offset, size) : new Uint8Array(_constants.default.CHR_RAM_PAGES * _constants.default.CHR_ROM_PAGE_SIZE);
  }

  /** Returns the header data. */
  get header() {
    if (this.__header) return this.__header;
    const flags6 = this.bytes[6];
    const flags7 = this.bytes[7];
    const prgRomPages = this.bytes[4];
    const chrRomPages = this.bytes[5];
    if (prgRomPages === 0) throw new Error("Invalid header: No PRG ROM pages!");
    return this.__header = {
      prgRomPages,
      chrRomPages: chrRomPages || _constants.default.CHR_RAM_PAGES,
      usesChrRam: chrRomPages === 0,
      mirroring: _helpers.Byte.getBit(flags6, 3) === 1 ? "FOUR_SCREENS" : _helpers.Byte.getBit(flags6, 0) === 1 ? "VERTICAL" : "HORIZONTAL",
      hasTrainerBeforeProgram: !!_helpers.Byte.getBit(flags6, 2),
      mapperId: _helpers.Byte.setBits(_helpers.Byte.getBits(flags6, 4, 4), 4, 4, _helpers.Byte.getBits(flags7, 4, 4))
    };
  }

  /** Returns the first 3 ASCII bytes of the header. It should return "NES". */
  get magicNumber() {
    return Array.from(this._getBytes(0, 3)).map(char => String.fromCharCode(char)).join("");
  }
  _getBytes(offset, size) {
    return this.bytes.slice(offset, offset + size);
  }
  get _programOffset() {
    return _constants.default.ROM_HEADER_SIZE + (this.header.hasTrainerBeforeProgram ? _constants.default.ROM_TRAINER_SIZE : 0);
  }
  get _programSize() {
    return this.header.prgRomPages * _constants.default.PRG_ROM_PAGE_SIZE;
  }
}
exports.default = Cartridge;