nes-emu/ppu/registers/PPUScroll.js

A NES emulator

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = void 0;
var _registers = require("../../registers");
var _constants = _interopRequireDefault(require("../../constants"));
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
/**
 * PPU Scrolling Position Register (>> write twice, first X then Y)
 *
 * Changes the scroll position. Used to tell the PPU which pixel of the Name table
 * (selected through `PPUCtrl`) should be at the top left corner of the rendered screen.
 * Connected to `LoopyRegister`.
 */
class PPUScroll extends _registers.WriteOnlyInMemoryRegister {
  /**
   * Returns the scrolled X in Name table coordinates ([0..262]).
   * If this value overflows (> 255), switch the horizontal Name table.
   */
  scrolledX(x) {
    const {
      vAddress,
      fineX
    } = this.context.ppu.loopy;
    return vAddress.coarseX * _constants.default.TILE_LENGTH + fineX + x % _constants.default.TILE_LENGTH;
  }

  /** Returns the scrolled X in Name table coordinates ([0..255]). */
  scrolledY() {
    const {
      vAddress
    } = this.context.ppu.loopy;
    return vAddress.coarseY * _constants.default.TILE_LENGTH + vAddress.fineY;
  }

  /** Alternately writes the X and the Y coordinates of the scroll. */
  writeAt(__, byte) {
    this.context.ppu.loopy.onPPUScrollWrite(byte);
  }
}
exports.default = PPUScroll;