nes-emu/ppu/renderers/tables/Sprite.js

A NES emulator

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = void 0;
var _constants = _interopRequireDefault(require("../../../constants"));
var _helpers = require("../../../helpers");
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
/** A sprite containing an id, position, height, a tile id and some attributes.  */
class Sprite {
  constructor(id, x, y, patternTableId, tileId, attributes, is8x16) {
    this.id = id;
    this.x = x;
    this.y = y;
    this.patternTableId = patternTableId;
    this.tileId = tileId;
    this.attributes = attributes;
    this.is8x16 = is8x16;
  }

  /**
   * Returns the tile id for an `insideY` position.
   * The bottom part of a 8x16 sprite uses the next tile index.
   */
  tileIdFor(insideY) {
    let index = +(insideY >= _constants.default.TILE_LENGTH);
    if (this.is8x16 && this.flipY) index = +!index;
    return this.tileId + index;
  }

  /** Returns whether it should appear in a certain `scanline` or not. */
  shouldRenderInScanline(scanline) {
    const diffY = this.diffY(scanline);
    return diffY >= 0 && diffY < this.height;
  }

  /** Returns the difference between a `scanline` and sprite's Y coordinate. */
  diffY(scanline) {
    return scanline - this.y;
  }

  /** Returns the palette id of the sprite. */
  get paletteId() {
    return _constants.default.PALETTE_FOREGROUND_START + _helpers.Byte.getBits(this.attributes, _constants.default.SPRITE_ATTR_PALETTE_BITS_START, _constants.default.SPRITE_ATTR_PALETTE_BITS_SIZE);
  }

  /** Returns whether the sprite is in front of background or not. */
  get isInFrontOfBackground() {
    return !_helpers.Byte.getBit(this.attributes, _constants.default.SPRITE_ATTR_PRIORITY_BIT);
  }

  /** Returns whether the sprite is horizontally flipped or not. */
  get flipX() {
    return !!_helpers.Byte.getBit(this.attributes, _constants.default.SPRITE_ATTR_HORIZONTAL_FLIP_BIT);
  }

  /** Returns whether the sprite is vertically flipped or not. */
  get flipY() {
    return !!_helpers.Byte.getBit(this.attributes, _constants.default.SPRITE_ATTR_VERTICAL_FLIP_BIT);
  }

  /** Returns the sprite height. */
  get height() {
    return this.is8x16 ? 16 : 8;
  }
}
exports.default = Sprite;