broken-neees/Cartridge.js

A really broken NEEES emulator that introduces glitches and random bugs on purpose!

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = void 0;
var _byte = _interopRequireDefault(require("./lib/byte"));
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
const KB = 1024;
const HEADER_SIZE = 16;
const PRG_PAGE_SIZE = 16 * KB;
const CHR_PAGE_SIZE = 8 * KB;
class Cartridge {
  constructor(bytes) {
    this.bytes = bytes;
    this._checkMagicConstant();
    this.header = this._buildHeader();
  }

  // [!!!]
  get isBroken() {
    return !this.unbroken;
  }
  prg() {
    return this.bytes.slice(this._prgOffset(), this._prgOffset() + this._prgSize());
  }
  chr() {
    if (this.header.usesChrRam) return new Uint8Array(CHR_PAGE_SIZE);
    if (this.unbroken) {
      return this.bytes.slice(this._chrOffset(), this._chrOffset() + this._chrSize());
    } else {
      // [!!!]
      const size = this._chrSize();
      const bytes = new Uint8Array(size + 3);
      bytes.set(this.bytes.slice(this._chrOffset(), this._chrOffset() + size), 3);
      return bytes;
    }
  }
  _prgOffset() {
    return HEADER_SIZE + (this.header.has512BytePadding ? 512 : 0);
  }
  _prgSize() {
    return this.header.prgRomPages * PRG_PAGE_SIZE;
  }
  _chrOffset() {
    return this._prgOffset() + this._prgSize();
  }
  _chrSize() {
    return this.header.chrRomPages * CHR_PAGE_SIZE;
  }
  _buildHeader() {
    const prgRomPages = this.bytes[4];
    const chrRomPages = this.bytes[5];
    const flags6 = this.bytes[6];
    const flags7 = this.bytes[7];
    return {
      prgRomPages,
      chrRomPages,
      usesChrRam: chrRomPages === 0,
      has512BytePadding: _byte.default.getFlag(flags6, 2),
      hasPrgRam: _byte.default.getFlag(flags6, 1),
      mirroringId: _byte.default.getFlag(flags6, 3) ? "FOUR_SCREEN" : _byte.default.getFlag(flags6, 0) ? "VERTICAL" : "HORIZONTAL",
      mapperId: _byte.default.buildU8(_byte.default.highNybbleOf(flags7), _byte.default.highNybbleOf(flags6))
    };
  }
  _checkMagicConstant() {
    if (this.bytes[0] !== 0x4e || this.bytes[1] !== 0x45 || this.bytes[2] !== 0x53 || this.bytes[3] !== 0x1a) {
      throw new Error("Invalid ROM.");
    }
  }
}
exports.default = Cartridge;