Battle-for-Tismo/shared/game_state/visibility.js

// Fog of war and the grid walkers. Explored cells stay known; visible cells
// are the ones currently watched by territory and units.

import { key, parseKey } from "../hex.js";
import { UNIT_VISION, TERRITORY_VISION } from "./constants.js";
import { tileImprovementById } from "../data/improvements.js";
import { serializeSet } from "./helpers.js";

export const visibilityMethods = {
  isExplored(civ, coords) {
    const set = this.explored.get(civ);
    return set ? set.has(key(coords.x, coords.y)) : false;
  },

  isVisible(civ, coords) {
    const set = this.visible.get(civ);
    return set ? set.has(key(coords.x, coords.y)) : false;
  },

  canEnter(civ, proto, coords) {
    if (!proto || !this.isExplored(civ, coords)) return false;
    const tile = this.tiles[key(coords.x, coords.y)];
    if (!tile) return false;
    return proto.traversableTerrains.includes(tile.terrainClass);
  },

  _refreshVisibility() {
    this.visible = new Map();
    for (let i = 0; i < this.civilisations.length; i++) this.visible.set(i, new Set());
    for (const [civ, cells] of this._territoryByCiv) {
      for (const coords of cells) this._reveal(civ, coords, TERRITORY_VISION);
    }
    for (const unit of this.units) {
      const proto = this.unitProto(unit);
      this._reveal(unit.civ, unit.coords, (proto && proto.vision) || UNIT_VISION);
    }
    // Fortifications and radar towers watch their own neighbourhood too.
    for (const [k, id] of this.tileImprovements) {
      const proto = tileImprovementById(id);
      if (!proto || !proto.vision) continue;
      const owner = this.tileImprovementOwner.get(k);
      if (owner === undefined || owner < 0) continue;
      this._reveal(owner, parseKey(k), Math.max(UNIT_VISION, proto.vision));
    }
    // The visible sets only move here, so this counter lets a delta snapshot
    // omit the (large) per-viewer visible list until the next refresh.
    this._visibleVersion += 1;
  },

  _revealAll() {
    for (let i = 0; i < this.civilisations.length; i++) {
      this.explored.set(i, new Set(Object.keys(this.tiles)));
    }
  },

  _reveal(civ, center, radius) {
    if (!this.explored.has(civ)) this.explored.set(civ, new Set());
    if (!this.visible.has(civ)) this.visible.set(civ, new Set());
    const exploredCells = this.explored.get(civ);
    const visibleCells = this.visible.get(civ);
    let discovered = false;
    for (const coords of this._cellsInRadius(center, radius)) {
      const k = key(coords.x, coords.y);
      if (!exploredCells.has(k)) {
        exploredCells.add(k);
        discovered = true;
      }
      visibleCells.add(k);
    }
    if (discovered) this._serializedExplored.delete(civ);
  },

  _cachedExplored(civ) {
    if (!this._serializedExplored.has(civ)) {
      this._serializedExplored.set(civ, serializeSet(this.explored.get(civ) || new Set()));
    }
    return this._serializedExplored.get(civ);
  },

  // The viewer's currently visible tiles, flattened for the wire. The whole
  // visible set is rebuilt only on a visibility refresh, which bumps
  // `_visibleVersion`, so an unchanged fog is not re-walked on every broadcast.
  _cachedVisible(civ) {
    const cached = this._serializedVisible.get(civ);
    if (cached && cached.version === this._visibleVersion) return cached.value;
    const value = serializeSet(this.visible.get(civ) || new Set());
    this._serializedVisible.set(civ, { version: this._visibleVersion, value });
    return value;
  },

  _cellsInRadius(center, radius) {
    const result = [center];
    const visited = new Set([key(center.x, center.y)]);
    let frontier = [center];
    for (let step = 0; step < radius; step++) {
      const next = [];
      for (const coords of frontier) {
        for (const neighbour of this._neighbours(coords)) {
          const k = key(neighbour.x, neighbour.y);
          if (visited.has(k)) continue;
          visited.add(k);
          next.push(neighbour);
          result.push(neighbour);
        }
      }
      frontier = next;
    }
    return result;
  },

  _neighbours(coords) {
    const k = key(coords.x, coords.y);
    if (this._neighbourCache.has(k)) return this._neighbourCache.get(k);
    const result = this.topology.neighbours(coords.x, coords.y);
    this._neighbourCache.set(k, result);
    return result;
  },
};