Battle-for-Tismo/client/js/map_view/utils.js

// Pure helpers for the map view: geometry, path timing and colour blending.
// Nothing here touches the DOM or the MapView instance, so it is all trivially
// testable.

import { HEX_W, HEX_H } from "../../../shared/hex.js";
import { OVERVIEW_COLOURS, OVERVIEW_SEA } from "./constants.js";

export function parity(x) {
  return x & 1;
}

// Order-independent FNV-style hash of an [x, y, ...] entry array, used to skip
// rebuilding a layer when the snapshot did not actually change it.
export function hashEntries(entries) {
  let hash = 2166136261;
  for (const entry of entries) {
    hash = Math.imul(hash ^ (entry[0] + 4096), 16777619);
    hash = Math.imul(hash ^ (entry[1] + 4096), 16777619);
    hash = Math.imul(hash ^ (entry.length > 2 ? entry[2] + 8 : 0), 16777619);
  }
  return `${entries.length}:${(hash >>> 0).toString(36)}`;
}

// How far along its path a unit is, in segment-hours, from a snapshot.
export function hoursAlong(data, segmentHours) {
  const index = Math.min(data.pathIndex || 0, segmentHours.length);
  let total = 0;
  for (let i = 0; i < index; i++) total += segmentHours[i];
  return total + (data.progressHours || 0);
}

export function samePath(a, b) {
  if (a.length !== b.length) return false;
  for (let i = 0; i < a.length; i++) {
    if (a[i].x !== b[i].x || a[i].y !== b[i].y) return false;
  }
  return true;
}

// The segment index a motion is currently on and how far into it it is.
export function pathProgress(motion) {
  let remaining = motion.pathHours;
  let index = 0;
  while (index < motion.segmentHours.length) {
    const step = motion.segmentHours[index];
    if (step <= 0) {
      index += 1;
      continue;
    }
    if (remaining < step) break;
    remaining -= step;
    index += 1;
  }
  return { index, remaining };
}

export function nearestCorners(center, target) {
  const half = { x: HEX_W / 2, y: HEX_H / 2 };
  const corners = [
    { x: half.x, y: 0 },
    { x: half.x * 0.5, y: -half.y },
    { x: -half.x * 0.5, y: -half.y },
    { x: -half.x, y: 0 },
    { x: -half.x * 0.5, y: half.y },
    { x: half.x * 0.5, y: half.y },
  ];
  let first = 0;
  let second = 1;
  let firstDistance = Infinity;
  let secondDistance = Infinity;
  for (let i = 0; i < corners.length; i++) {
    const point = { x: center.x + corners[i].x, y: center.y + corners[i].y };
    const distance = (point.x - target.x) ** 2 + (point.y - target.y) ** 2;
    if (distance < firstDistance) {
      secondDistance = firstDistance;
      second = first;
      firstDistance = distance;
      first = i;
    } else if (distance < secondDistance) {
      secondDistance = distance;
      second = i;
    }
  }
  return [
    { x: center.x + corners[first].x, y: center.y + corners[first].y },
    { x: center.x + corners[second].x, y: center.y + corners[second].y },
  ];
}

// Signed distance to nudge an edge segment along its normal so it moves towards
// `center` (the owning tile). Used to keep neighbours' borders side by side
// instead of overlapping on the shared edge.
export function inwardOffset(a, b, center, distance) {
  const dx = b.x - a.x;
  const dy = b.y - a.y;
  const length = Math.hypot(dx, dy) || 1;
  const nx = -dy / length;
  const ny = dx / length;
  const midX = (a.x + b.x) / 2;
  const midY = (a.y + b.y) / 2;
  const dot = (center.x - midX) * nx + (center.y - midY) * ny;
  return dot >= 0 ? distance : -distance;
}

export function makeSegment(a, b, colour, width, offset = 0) {
  const div = document.createElement("div");
  div.className = "border-seg";
  const dx = b.x - a.x;
  const dy = b.y - a.y;
  const length = Math.hypot(dx, dy);
  const angle = Math.atan2(dy, dx);
  div.style.left = `${a.x}px`;
  div.style.top = `${a.y - width / 2}px`;
  div.style.width = `${length}px`;
  div.style.height = `${width}px`;
  div.style.background = colour;
  div.style.transform = offset === 0
    ? `rotate(${angle}rad)`
    : `rotate(${angle}rad) translateY(${offset}px)`;
  div.style.borderRadius = `${width / 2}px`;
  return div;
}

export function overviewColour(tile) {
  if (tile.terrainType && OVERVIEW_COLOURS[tile.terrainType]) {
    return OVERVIEW_COLOURS[tile.terrainType];
  }
  return tile.terrainClass === "Sea" ? OVERVIEW_SEA : OVERVIEW_COLOURS.Land;
}

// Mixes two #rrggbb colours, `t` being how much of `b` to use.
export function blendColours(a, b, t) {
  const ca = parseColour(a);
  const cb = parseColour(b);
  const mix = (i) => Math.round(ca[i] + (cb[i] - ca[i]) * t);
  return `rgb(${mix(0)}, ${mix(1)}, ${mix(2)})`;
}

function parseColour(value) {
  const hex = value.charAt(0) === "#" ? value.slice(1) : value;
  return [
    parseInt(hex.slice(0, 2), 16),
    parseInt(hex.slice(2, 4), 16),
    parseInt(hex.slice(4, 6), 16),
  ];
}

export function clamp(value, min, max) {
  if (min > max) return (min + max) / 2;
  return Math.max(min, Math.min(max, value));
}