nes-emu/ppu/registers/LoopyAddress.js

A NES emulator

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = void 0;
var _constants = _interopRequireDefault(require("../../constants"));
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
/**
 * A VRAM address, used for fetching the right tile during render.
 * yyy NN YYYYY XXXXX
 * ||| || ||||| +++++-- coarse X scroll
 * ||| || +++++-------- coarse Y scroll
 * ||| ++-------------- nametable select
 * +++----------------- fine Y scroll
 */
class LoopyAddress {
  constructor() {
    this.coarseX = 0;
    this.coarseY = 0;
    this.nameTableId = 0;
    this.fineY = 0;
  }

  /** Increments X, wrapping when needed. */
  incrementX() {
    if (this.coarseX === 31) {
      this.coarseX = 0;
      this._switchHorizontalNameTable();
    } else {
      this.coarseX++;
    }
  }

  /** Increments Y, wrapping when needed. */
  incrementY() {
    if (this.fineY < 7) {
      this.fineY++;
    } else {
      this.fineY = 0;
      if (this.coarseY === 29) {
        this.coarseY = 0;
        this._switchVerticalNameTable();
      } else if (this.coarseY === 31) {
        this.coarseY = 0;
      } else {
        this.coarseY++;
      }
    }
  }

  /**
   * Returns the value as a 14-bit number.
   * The v register has 15 bits, but the PPU memory space is only 14 bits wide.
   * The highest bit is unused for access through $2007.
   */
  to14BitNumber() {
    return this.toNumber() & 0b11111111111111;
  }

  /** Converts the address to a 15-bit number. */
  toNumber() {
    return this.coarseX << _constants.default.LOOPY_ADDR_COARSE_X_OFFSET | this.coarseY << _constants.default.LOOPY_ADDR_COARSE_Y_OFFSET | this.nameTableId << _constants.default.LOOPY_ADDR_BASE_NAME_TABLE_ID_OFFSET | this.fineY << _constants.default.LOOPY_ADDR_FINE_Y_OFFSET;
  }

  /** Updates the address from a 15-bit number. */
  update(number) {
    this.coarseX = number >> _constants.default.LOOPY_ADDR_COARSE_X_OFFSET & _constants.default.LOOPY_ADDR_COARSE_X_MASK;
    this.coarseY = number >> _constants.default.LOOPY_ADDR_COARSE_Y_OFFSET & _constants.default.LOOPY_ADDR_COARSE_Y_MASK;
    this.nameTableId = number >> _constants.default.LOOPY_ADDR_BASE_NAME_TABLE_ID_OFFSET & _constants.default.LOOPY_ADDR_BASE_NAME_TABLE_ID_MASK;
    this.fineY = number >> _constants.default.LOOPY_ADDR_FINE_Y_OFFSET & _constants.default.LOOPY_ADDR_FINE_Y_MASK;
  }
  _switchHorizontalNameTable() {
    this.nameTableId = this.nameTableId ^ 0b1;
  }
  _switchVerticalNameTable() {
    this.nameTableId = this.nameTableId ^ 0b10;
  }
}
exports.default = LoopyAddress;