bworld/common/worldgen/overworld.ts

// fills a chunk with the overworld: the terrain's density sampled on a coarse grid and interpolated (minecraft's
// noise cells), caves cut out of it, water up to sea level, then biomes and their surface blocks
import { CHUNK_AREA, CHUNK_HEIGHT, CHUNK_SIZE, SEA_LEVEL } from "$/common/constants.ts";
import { OctaveNoise2D } from "./noise.ts";
import { OverworldTerrain, TerrainColumn } from "./terrain.ts";

// density is sampled every CELL_WIDTH blocks across and CELL_HEIGHT up, caves every CAVE_CELL_HEIGHT up since
// tunnels are thinner than terrain features
const CELL_WIDTH = 4;
const CELL_HEIGHT = 8;
const CAVE_CELL_HEIGHT = 4;
const CORNERS = CHUNK_SIZE / CELL_WIDTH + 1;
const TERRAIN_LEVELS = CHUNK_HEIGHT / CELL_HEIGHT + 1;
const CAVE_LEVELS = CHUNK_HEIGHT / CAVE_CELL_HEIGHT + 1;

// surface blocks only go this far below the ground's height, so cave floors stay stone
const SURFACE_REACH = 20;
// a column is a cliff when its ground is this much higher or lower than a neighbor's
const STEEP = 3.5;
// snow covers the tops of everything above this, give or take
const SNOW_LINE = SEA_LEVEL + 112;

// the blocks the overworld is made of, as numeric ids
export interface OverworldBlocks {
	stone: number;
	dirt: number;
	grass: number;
	sand: number;
	snow: number;
	water: number;
}

type Palette = "stone" | "dirt" | "grass" | "sand" | "snow";

// how a biome covers its ground, like minecraft's surface rules
interface Surface {
	top: Palette;
	filler: Palette;
	filler_depth: number;
	// the ground's cover under water
	underwater_top: Palette;
	underwater_filler: Palette;
	// cliffs show bare stone instead of top
	bare_cliffs: boolean;
	// stripes of sand, stone and dirt down the cliffs, like badlands
	strata?: boolean;
}

const GRASSY: Surface = {
	top: "grass",
	filler: "dirt",
	filler_depth: 3,
	underwater_top: "dirt",
	underwater_filler: "dirt",
	bare_cliffs: true,
};
const SANDY: Surface = {
	top: "sand",
	filler: "sand",
	filler_depth: 4,
	underwater_top: "sand",
	underwater_filler: "sand",
	bare_cliffs: false,
};
const SNOWY: Surface = { ...GRASSY, top: "snow" };
const STONY: Surface = {
	...GRASSY,
	top: "stone",
	filler: "stone",
	underwater_top: "stone",
	underwater_filler: "stone",
};
const SEA_FLOOR: Surface = { ...SANDY, filler_depth: 3 };

// every biome the overworld has, and its surface. names follow minecraft's and terralith's
export const BIOMES: Record<string, Surface> = {
	"bworld:deep_ocean": SEA_FLOOR,
	"bworld:deep_frozen_ocean": SEA_FLOOR,
	"bworld:deep_lukewarm_ocean": SEA_FLOOR,
	"bworld:ocean": SEA_FLOOR,
	"bworld:frozen_ocean": SEA_FLOOR,
	"bworld:warm_ocean": SEA_FLOOR,
	"bworld:river": { ...GRASSY, underwater_top: "sand", underwater_filler: "sand" },
	"bworld:frozen_river": { ...SNOWY, underwater_top: "sand", underwater_filler: "sand" },
	"bworld:beach": SANDY,
	"bworld:snowy_beach": { ...SANDY, top: "snow" },
	"bworld:stony_shore": STONY,
	"bworld:plains": GRASSY,
	"bworld:meadow": GRASSY,
	"bworld:forest": GRASSY,
	"bworld:dark_forest": GRASSY,
	"bworld:swamp": { ...GRASSY, bare_cliffs: false },
	"bworld:taiga": GRASSY,
	"bworld:snowy_plains": SNOWY,
	"bworld:snowy_taiga": SNOWY,
	"bworld:savanna": GRASSY,
	"bworld:jungle": GRASSY,
	"bworld:desert": SANDY,
	"bworld:alpine_highlands": GRASSY,
	"bworld:snowy_slopes": SNOWY,
	"bworld:stony_peaks": STONY,
	"bworld:jagged_peaks": { ...STONY, top: "snow" },
	"bworld:frozen_peaks": { ...SNOWY, filler: "stone" },
	"bworld:yosemite_cliffs": GRASSY,
	"bworld:snowy_cliffs": SNOWY,
	"bworld:painted_mountains": { ...SANDY, filler_depth: 2, bare_cliffs: true, strata: true },
	"bworld:stony_spires": GRASSY,
	"bworld:shattered_savanna": GRASSY,
	"bworld:skylands": GRASSY,
};

// picks a column's biome from its climate and shape, like minecraft's multi noise biome source
export function pick_biome(column: TerrainColumn, surface_y: number, steep: boolean): string {
	const { continentalness: c, erosion: e, pv, temperature: t, humidity: h } = column.climate;
	const frozen = t < -0.65;
	const cold = t < -0.3;
	const warm = t > 0.2;
	const hot = t > 0.55;

	if (column.island && surface_y >= column.island.bottom) {
		return "bworld:skylands";
	}

	if (surface_y < SEA_LEVEL - 1) {
		if (pv < -0.7 && c > -0.12) return frozen ? "bworld:frozen_river" : "bworld:river";
		if (c < -0.45) {
			return frozen ? "bworld:deep_frozen_ocean" : hot ? "bworld:deep_lukewarm_ocean" : "bworld:deep_ocean";
		}
		return frozen ? "bworld:frozen_ocean" : hot ? "bworld:warm_ocean" : "bworld:ocean";
	}
	if (c < -0.04 && surface_y <= SEA_LEVEL + 4) {
		return steep ? "bworld:stony_shore" : cold ? "bworld:snowy_beach" : "bworld:beach";
	}
	if (pv < -0.8 && c > -0.12 && surface_y <= SEA_LEVEL + 1) {
		return frozen ? "bworld:frozen_river" : "bworld:river";
	}

	const above = surface_y - SEA_LEVEL;
	if (above > 105) {
		if (cold) return "bworld:frozen_peaks";
		return column.jaggedness > 0.35 ? "bworld:jagged_peaks" : "bworld:stony_peaks";
	}
	if (column.plateau > 0.5) {
		if (hot && h < 0.1) return "bworld:painted_mountains";
		return cold ? "bworld:snowy_cliffs" : "bworld:yosemite_cliffs";
	}
	if (column.shattered > 0.5) {
		return warm ? "bworld:shattered_savanna" : "bworld:stony_spires";
	}
	if (above > 60) {
		return cold ? "bworld:snowy_slopes" : "bworld:alpine_highlands";
	}
	if (above > 30 && e > -0.2 && !cold && h > -0.3) {
		return "bworld:meadow";
	}

	if (frozen) return h > 0 ? "bworld:snowy_taiga" : "bworld:snowy_plains";
	if (cold) return h > 0 ? "bworld:taiga" : "bworld:plains";
	if (hot) return h < -0.2 ? "bworld:desert" : h < 0.4 ? "bworld:savanna" : "bworld:jungle";
	if (warm) return h < -0.3 ? "bworld:savanna" : h > 0.6 ? "bworld:jungle" : "bworld:forest";
	if (h > 0.5 && e > 0.4) return "bworld:swamp";
	return h < -0.35 ? "bworld:plains" : h < 0.45 ? "bworld:forest" : "bworld:dark_forest";
}

interface SeedGenerators {
	terrain: OverworldTerrain;
	snow_line: OctaveNoise2D;
	strata: OctaveNoise2D;
}

const generators = new Map<string, SeedGenerators>();

function generators_for(seed: string): SeedGenerators {
	let found = generators.get(seed);
	if (!found) {
		found = {
			terrain: new OverworldTerrain(seed),
			snow_line: new OctaveNoise2D(seed, "snow_line", 96, [1, 1]),
			strata: new OctaveNoise2D(seed, "strata", 128, [1]),
		};
		generators.set(seed, found);
	}
	return found;
}

// fills blocks (indexed y * CHUNK_AREA + z * CHUNK_SIZE + x) and each column's surface height and biome
export function generate_overworld(
	blocks: Uint32Array,
	heights: Int32Array,
	biomes: string[],
	chunk_x: number,
	chunk_z: number,
	seed: string,
	ids: OverworldBlocks,
) {
	const { terrain, snow_line, strata } = generators_for(seed);
	const x0 = chunk_x * CHUNK_SIZE;
	const z0 = chunk_z * CHUNK_SIZE;

	// density at the corners of every cell
	const corner_columns: TerrainColumn[] = [];
	for (let cz = 0; cz < CORNERS; cz++) {
		for (let cx = 0; cx < CORNERS; cx++) {
			corner_columns.push(terrain.column(x0 + cx * CELL_WIDTH, z0 + cz * CELL_WIDTH));
		}
	}
	const solid = new Float32Array(CORNERS * CORNERS * TERRAIN_LEVELS);
	const caves = new Float32Array(CORNERS * CORNERS * CAVE_LEVELS);
	for (let i = 0; i < corner_columns.length; i++) {
		const column = corner_columns[i];
		const x = x0 + (i % CORNERS) * CELL_WIDTH;
		const z = z0 + Math.floor(i / CORNERS) * CELL_WIDTH;
		for (let level = 0; level < TERRAIN_LEVELS; level++) {
			solid[i * TERRAIN_LEVELS + level] = terrain.density(column, x, level * CELL_HEIGHT, z);
		}
		// caves only matter below the ground, skip the sky above it
		const cave_top = column.height + CAVE_CELL_HEIGHT;
		for (let level = 0; level < CAVE_LEVELS; level++) {
			const y = level * CAVE_CELL_HEIGHT;
			caves[i * CAVE_LEVELS + level] = y > cave_top ? 1 : terrain.cave(column, x, y, z);
		}
	}

	// every column of the chunk plus a ring around it, for how steep the ground is
	const columns: TerrainColumn[] = [];
	const ring = CHUNK_SIZE + 2;
	for (let z = -1; z <= CHUNK_SIZE; z++) {
		for (let x = -1; x <= CHUNK_SIZE; x++) {
			columns.push(terrain.column(x0 + x, z0 + z));
		}
	}
	const column_at = (x: number, z: number) => columns[(z + 1) * ring + x + 1];

	for (let z = 0; z < CHUNK_SIZE; z++) {
		for (let x = 0; x < CHUNK_SIZE; x++) {
			fill_column(x, z);
		}
	}

	function fill_column(x: number, z: number) {
		const cell_x = Math.min(Math.floor(x / CELL_WIDTH), CORNERS - 2);
		const cell_z = Math.min(Math.floor(z / CELL_WIDTH), CORNERS - 2);
		const tx = (x - cell_x * CELL_WIDTH) / CELL_WIDTH;
		const tz = (z - cell_z * CELL_WIDTH) / CELL_WIDTH;
		const c00 = cell_z * CORNERS + cell_x;
		const c10 = c00 + 1;
		const c01 = c00 + CORNERS;
		const c11 = c01 + 1;
		const w00 = (1 - tx) * (1 - tz);
		const w10 = tx * (1 - tz);
		const w01 = (1 - tx) * tz;
		const w11 = tx * tz;
		// one column through the corner grid, blended between its four corners
		const blend = (grid: Float32Array, levels: number, level: number) =>
			grid[c00 * levels + level] * w00 + grid[c10 * levels + level] * w10 +
			grid[c01 * levels + level] * w01 + grid[c11 * levels + level] * w11;

		const is_solid = new Uint8Array(CHUNK_HEIGHT);
		for (let y = 0; y < CHUNK_HEIGHT; y++) {
			const level = Math.min(Math.floor(y / CELL_HEIGHT), TERRAIN_LEVELS - 2);
			const t = (y - level * CELL_HEIGHT) / CELL_HEIGHT;
			let density = blend(solid, TERRAIN_LEVELS, level) * (1 - t) + blend(solid, TERRAIN_LEVELS, level + 1) * t;
			if (density > 0) {
				const cave_level = Math.min(Math.floor(y / CAVE_CELL_HEIGHT), CAVE_LEVELS - 2);
				const ct = (y - cave_level * CAVE_CELL_HEIGHT) / CAVE_CELL_HEIGHT;
				const cave = blend(caves, CAVE_LEVELS, cave_level) * (1 - ct) +
					blend(caves, CAVE_LEVELS, cave_level + 1) * ct;
				density = Math.min(density, cave);
			}
			is_solid[y] = density > 0 ? 1 : 0;
		}

		const column = column_at(x, z);
		let surface_y = CHUNK_HEIGHT - 1;
		while (surface_y > 0 && !is_solid[surface_y]) surface_y--;

		const ground = column.height;
		const neighbors = [column_at(x - 1, z), column_at(x + 1, z), column_at(x, z - 1), column_at(x, z + 1)];
		const steep = neighbors.some((neighbor) => Math.abs(neighbor.height - ground) >= STEEP);
		const biome = pick_biome(column, surface_y, steep);
		const surface = BIOMES[biome];
		const snow_y = SNOW_LINE + snow_line.sample(x0 + x, z0 + z) * 10;
		const strata_offset = strata.sample(x0 + x, z0 + z) * 4;
		const island_bottom = column.island ? column.island.bottom - 2 : Infinity;

		heights[z * CHUNK_SIZE + x] = surface_y;
		biomes[z * CHUNK_SIZE + x] = biome;

		const index = (y: number) => y * CHUNK_AREA + z * CHUNK_SIZE + x;
		// solid blocks since the last air going down, 0 is a block with air on top
		let depth = -1;
		// nothing but air (and sky islands) above so far: water fills it up to sea level
		let open_sky = true;
		// whether the ground's surface is under water, for its cover
		let underwater = false;
		for (let y = CHUNK_HEIGHT - 1; y >= 0; y--) {
			if (!is_solid[y]) {
				depth = -1;
				if (open_sky && y < SEA_LEVEL) {
					blocks[index(y)] = ids.water;
				}
				continue;
			}
			depth += 1;
			const in_island = y >= island_bottom;
			if (open_sky && !in_island) {
				open_sky = false;
				underwater = y < SEA_LEVEL - 1;
			}

			// surface rules reach the ground and anything above it, not cave floors
			let block: Palette = "stone";
			if (y >= ground - SURFACE_REACH || in_island) {
				const wet = underwater && !in_island;
				if (surface.strata && depth > 0 && y > SEA_LEVEL) {
					block = strata_block(y + strata_offset);
				} else if (depth === 0) {
					if (wet) block = surface.underwater_top;
					else if (y >= snow_y && !in_island) block = steep ? "stone" : "snow";
					else block = steep && surface.bare_cliffs ? "stone" : surface.top;
				} else if (depth <= surface.filler_depth) {
					block = wet ? surface.underwater_filler : surface.filler;
				}
			}
			blocks[index(y)] = ids[block];
		}
	}
}

// the bands down a painted mountain's cliffs
function strata_block(y: number): Palette {
	const band = ((Math.floor(y / 3) % 6) + 6) % 6;
	return band === 1 || band === 4 ? "stone" : band === 3 ? "dirt" : "sand";
}