Fantasy-Map-Generator/src/modules/coastline.js

import * as d3 from "d3";

import {ERROR, TIME} from "config/logging";
import {clipPoly} from "utils/lineUtils";
import {round} from "utils/stringUtils";
import {Ruler} from "modules/measurers";

// Detect and draw the coastline
export function drawCoastline() {
  TIME && console.time("drawCoastline");

  const {cells, vertices, features} = pack;
  const n = cells.i.length;

  const used = new Uint8Array(features.length); // store connected features
  const largestLand = d3.scan(
    features.map(f => (f.land ? f.cells : 0)),
    (a, b) => b - a
  );

  const landMask = defs.select("#land");
  const waterMask = defs.select("#water");
  const lineGen = d3.line().curve(d3.curveBasisClosed);

  for (const i of cells.i) {
    const startFromEdge = !i && cells.h[i] >= 20;
    if (!startFromEdge && cells.t[i] !== -1 && cells.t[i] !== 1) continue; // non-edge cell
    const f = cells.f[i];
    if (used[f]) continue; // already connected
    if (features[f].type === "ocean") continue; // ocean cell

    const type = features[f].type === "lake" ? 1 : -1; // type value to search for
    const start = findStart(i, type);
    if (start === -1) continue; // cannot start here
    let vchain = connectVertices(start, type);
    if (features[f].type === "lake") relax(vchain, 1.2);
    used[f] = 1;
    let points = clipPoly(vchain.map(v => vertices.p[v]));
    const area = d3.polygonArea(points); // area with lakes/islands
    if (area > 0 && features[f].type === "lake") {
      points = points.reverse();
      vchain = vchain.reverse();
    }

    features[f].area = Math.abs(area);
    features[f].vertices = vchain;

    const path = round(lineGen(points));
    if (features[f].type === "lake") {
      landMask
        .append("path")
        .attr("d", path)
        .attr("fill", "black")
        .attr("id", "land_" + f);
      // waterMask.append("path").attr("d", path).attr("fill", "white").attr("id", "water_"+id); // uncomment to show over lakes
      lakes
        .select("#freshwater")
        .append("path")
        .attr("d", path)
        .attr("id", "lake_" + f)
        .attr("data-f", f); // draw the lake
    } else {
      landMask
        .append("path")
        .attr("d", path)
        .attr("fill", "white")
        .attr("id", "land_" + f);
      waterMask
        .append("path")
        .attr("d", path)
        .attr("fill", "black")
        .attr("id", "water_" + f);
      const g = features[f].group === "lake_island" ? "lake_island" : "sea_island";
      coastline
        .select("#" + g)
        .append("path")
        .attr("d", path)
        .attr("id", "island_" + f)
        .attr("data-f", f); // draw the coastline
    }

    // draw ruler to cover the biggest land piece
    if (f === largestLand) {
      const from = points[d3.scan(points, (a, b) => a[0] - b[0])];
      const to = points[d3.scan(points, (a, b) => b[0] - a[0])];
      rulers.create(Ruler, [from, to]);
    }
  }

  // find cell vertex to start path detection
  function findStart(i, t) {
    if (t === -1 && cells.b[i]) return cells.v[i].find(v => vertices.c[v].some(c => c >= n)); // map border cell
    const filtered = cells.c[i].filter(c => cells.t[c] === t);
    const index = cells.c[i].indexOf(d3.min(filtered));
    return index === -1 ? index : cells.v[i][index];
  }

  // connect vertices to chain
  function connectVertices(start, t) {
    const chain = []; // vertices chain to form a path
    for (let i = 0, current = start; i === 0 || (current !== start && i < 50000); i++) {
      const prev = chain[chain.length - 1]; // previous vertex in chain
      chain.push(current); // add current vertex to sequence
      const c = vertices.c[current]; // cells adjacent to vertex
      const v = vertices.v[current]; // neighboring vertices
      const c0 = c[0] >= n || cells.t[c[0]] === t;
      const c1 = c[1] >= n || cells.t[c[1]] === t;
      const c2 = c[2] >= n || cells.t[c[2]] === t;
      if (v[0] !== prev && c0 !== c1) current = v[0];
      else if (v[1] !== prev && c1 !== c2) current = v[1];
      else if (v[2] !== prev && c0 !== c2) current = v[2];
      if (current === chain[chain.length - 1]) {
        ERROR && console.error("Next vertex is not found");
        break;
      }
    }
    return chain;
  }

  // move vertices that are too close to already added ones
  function relax(vchain, r) {
    const p = vertices.p,
      tree = d3.quadtree();

    for (let i = 0; i < vchain.length; i++) {
      const v = vchain[i];
      let [x, y] = [p[v][0], p[v][1]];
      if (i && vchain[i + 1] && tree.find(x, y, r) !== undefined) {
        const v1 = vchain[i - 1];
        const v2 = vchain[i + 1];
        const [x1, y1] = [p[v1][0], p[v1][1]];
        const [x2, y2] = [p[v2][0], p[v2][1]];
        [x, y] = [(x1 + x2) / 2, (y1 + y2) / 2];
        p[v] = [x, y];
      }
      tree.add([x, y]);
    }
  }

  TIME && console.timeEnd("drawCoastline");
}