2024.js/island/grid.ts

import { Prng, mulberry32 } from "../lib/prng";
import { BEACH, ICECAP, LIGHT_FOREST, MOUNTAIN, WATER } from "./data";

export class IslandGrid {
  data: number[];
  rng: Prng;

  basePos: number;
  lobePos1: number;
  lobePos2: number;

  done = false;

  constructor(public width: number, public height: number, seed: number) {
    this.data = Array(width * height).fill(0);
    this.rng = mulberry32(seed);

    this.basePos = this.data.length >> 1;
    this.lobePos1 = this.xy(
      (width >> 1) + (this.rng() % 48) - 24,
      (height >> 1) + (this.rng() % 48) - 24
    );
    this.lobePos2 = this.xy(
      (width >> 1) + (this.rng() % 48) - 24,
      (height >> 1) + (this.rng() % 48) - 24
    );
  }

  public xy(x: number, y: number): number {
    return (
      (((x % this.width) + this.width) % this.width) +
      this.width * (((y % this.height) + this.height) % this.height)
    );
  }

  public floodSearch(
    startPos: number,
    shouldExpand: (tile: number) => boolean
  ): number[] {
    const len = this.data.length;
    const width = this.width;
    const seen = new Uint8Array(len);

    const hitPositions: number[] = [];

    function enqueue(pos: number) {
      if (!seen[pos]) {
        hitPositions.push(pos);
        seen[pos] = 1;
      }
    }

    enqueue(startPos);

    for (let i = 0; i < hitPositions.length; i++) {
      const pos = hitPositions[i];
      if (shouldExpand(this.data[pos])) {
        enqueue((pos - width) % len);
        enqueue((pos - 1) % len);
        enqueue((pos + 1) % len);
        enqueue((pos + width) % len);
      }
    }

    return hitPositions;
  }

  public drop(pos: number): void {
    const lowerNeighbors: number[] = [];

    const check = (adjPos: number) => {
      if (this.data[adjPos] < this.data[pos]) {
        lowerNeighbors.push(adjPos);
      }
    };

    // try to roll in cardinal directions

    check((pos - this.width) % this.data.length);
    check((pos - 1) % this.data.length);
    check((pos + 1) % this.data.length);
    check((pos + this.width) % this.data.length);

    if (lowerNeighbors.length > 0) {
      const downhill = lowerNeighbors[this.rng() % lowerNeighbors.length];
      return this.drop(downhill);
    }

    // try to roll in diagonal directions

    check((pos - this.width - 1) % this.data.length);
    check((pos - this.width + 1) % this.data.length);
    check((pos + this.width - 1) % this.data.length);
    check((pos + this.width + 1) % this.data.length);

    if (lowerNeighbors.length > 0) {
      const downhill = lowerNeighbors[this.rng() % lowerNeighbors.length];
      return this.drop(downhill);
    }

    // flat, increase elevation
    const newValue = ++this.data[pos];
    if (newValue == ICECAP) {
      this.done = true;
    }
  }

  public dropWithin(tiles: number[]) {
    if (tiles.length > 0) {
      this.drop(tiles[this.rng() % tiles.length]);
    }
  }

  public step() {
    const lowlandTiles1 = this.floodSearch(
      this.lobePos1,
      (tile) => tile > WATER
    );
    const lowlandTiles2 = this.floodSearch(
      this.lobePos2,
      (tile) => tile > WATER
    );

    // grow shore
    const shoreTiles1 = lowlandTiles1.filter((pos) => this.data[pos] == WATER);
    this.dropWithin(shoreTiles1);
    const shoreTiles2 = lowlandTiles2.filter((pos) => this.data[pos] == WATER);
    this.dropWithin(shoreTiles2);

    // seed beach
    const beachTiles = lowlandTiles1.filter((pos) => this.data[pos] == BEACH);
    this.dropWithin(beachTiles);

    // expand forest
    const forestLobe = this.floodSearch(this.lobePos1, (tile) => tile > BEACH);
    const forestTiles = forestLobe.filter(
      (pos) => this.data[pos] == LIGHT_FOREST
    );
    this.dropWithin(forestTiles);
    this.dropWithin(forestTiles);
    this.dropWithin(forestTiles);

    // form mountain
    const mountainTiles = this.floodSearch(
      this.basePos,
      (tile) => tile > MOUNTAIN
    );
    this.dropWithin(mountainTiles); // GENERATOR

    // const erodePos = islandTiles[islands.rng() % islandTiles.length];
    // islands.data[erodePos] = Math.max(islands.data[erodePos] - 1, 0);
  }
}