silphius/app/util/math.js

export const {
  abs,
  acos,
  acosh,
  asin,
  asinh,
  atan,
  atanh,
  atan2,
  ceil,
  cbrt,
  expm1,
  clz32,
  cos,
  cosh,
  exp,
  floor,
  fround,
  hypot,
  imul,
  log,
  log1p,
  log2,
  log10,
  max,
  min,
  round,
  sign,
  sin,
  sinh,
  sqrt,
  tan,
  tanh,
  trunc,
  E,
  LN10,
  LN2,
  LOG10E,
  LOG2E,
  PI,
  SQRT1_2,
  SQRT2,
} = Math;

export const TAU = Math.PI * 2;

export function bresenham({x: x1, y: y1}, {x: x2, y: y2}) {
  const points = [];
  let x; let y; let px; let py; let xe; let ye;
  const dx = x2 - x1;
  const dy = y2 - y1;
  const dx1 = Math.abs(dx);
  const dy1 = Math.abs(dy);
  px = 2 * dy1 - dx1;
  py = 2 * dx1 - dy1;
  if (dy1 <= dx1) {
    if (dx >= 0) {
      x = x1; y = y1; xe = x2;
    }
    else {
      x = x2; y = y2; xe = x1;
    }
    points.push({x, y});
    for (let i = 0; x < xe; i++) {
      x += 1;
      if (px < 0) {
        px += 2 * dy1;
      }
      else {
        if ((dx < 0 && dy < 0) || (dx > 0 && dy > 0)) {
          y += 1;
        }
        else {
          y -= 1;
        }
        px += 2 * (dy1 - dx1);
      }
      points.push({x, y});
    }
  }
  else {
    if (dy >= 0) {
      x = x1; y = y1; ye = y2;
    }
    else {
      x = x2; y = y2; ye = y1;
    }
    points.push({x, y});
    for (let i = 0; y < ye; i++) {
      y += 1;
      if (py <= 0) {
        py += 2 * dx1;
      }
      else {
        if ((dx < 0 && dy < 0) || (dx > 0 && dy > 0)) {
          x += 1;
        }
        else {
          x -= 1;
        }
        py += 2 * (dx1 - dy1);
      }
      points.push({x, y});
    }
  }
  return points;
}

export function clamp(n, min, max) {
  return Math.max(min, Math.min(max, n));
}

export function distance({x: lx, y: ly}, {x: rx, y: ry}) {
  const xd = lx - rx;
  const yd = ly - ry;
  return Math.sqrt(xd * xd + yd * yd);
}

export function floodwalk2D(eligible, data, {x, y, w, h}, {diagonal = false} = {}) {
  const n = data.length;
  let i = x + w * y;
  const points = new Set();
  if (i < 0 || i >= n) {
    return points;
  }
  const seen = [];
  seen[-1] = true;
  seen[i] = true;
  const todo = [i];
  while (todo.length > 0) {
    i = todo.pop();
    const v = data[i];
    if (!eligible.has(v)) {
      continue;
    }
    points.add(i);
    const xx = i % w;
    const yy = Math.floor(i / w);
    const us = yy >= 1;
    const rs = xx + 1 < w;
    const ds = yy + 1 < h;
    const ls = xx >= 1;
    const sel = [
      us ? i - w : -1,
      rs ? i + 1 : -1,
      ds ? i + w : -1,
      ls ? i - 1 : -1,
      ...(
        diagonal
        ? [
          us && rs ? i - w + 1 : -1,
          rs && ds ? i + w + 1 : -1,
          ds && ls ? i + w - 1 : -1,
          ls && us ? i - w - 1 : -1,
        ]
        : []
      )
    ];
    for (let i = 0; i < sel.length; ++i) {
      const j = sel[i];
      if (!seen[j]) {
        todo.push(j);
        seen[j] = true;
      }
    }
  }
  return points;
}

export function intersects(l, r) {
  if (l.x0 > r.x1) return false;
  if (l.y0 > r.y1) return false;
  if (l.x1 < r.x0) return false;
  if (l.y1 < r.y0) return false;
  return true;
}

export function normalizeVector({x, y}) {
  if (0 === y && 0 === x) {
    return {x: 0, y: 0};
  }
  const k = 1 / Math.sqrt(x * x + y * y);
  return {x: x * k, y: y * k};
}

export function random() {
  return Math.random();
}

export function isCollinear({x: ax, y: ay}, {x: bx, y: by}, {x: cx, y: cy}) {
  return (ay - by) * (ax - cx) === (ay - cy) * (ax - bx);
}

export const directionToVector = [
  {x:  0, y: -1},
  {x:  1, y:  0},
  {x:  0, y:  1},
  {x: -1, y:  0},
];

export function ortho(points, k = {x: 1, y: 1}) {
  if (points.length < 4) {
    throw new TypeError('Math.ortho(): points.length < 4');
  }
  const index = Object.create(null);
  for (const i in points) {
    const point = points[i];
    if (!index[point.y]) {
      index[point.y] = Object.create(null);
    }
    index[point.y][point.x] = i;
  }
  const sorted = [points[0]];
  let direction = 0;
  let walk = 0;
  navigate:
  while (true) {
    for (let i = 0; i < 4; i++) {
      // ccw rotation
      const nextDirection = (i + direction + 3) & 3;
      const {x: px, y: py} = points[walk];
      const {x: dx, y: dy} = directionToVector[nextDirection];
      const nextIndex = index[py + k.y * dy]?.[px + k.x * dx];
      const nextPoint = points[nextIndex];
      // loop = done
      if (points[0] === nextPoint) {
        return sorted;
      }
      if (nextPoint) {
        direction = nextDirection;
        sorted.push(nextPoint);
        walk = nextIndex;
        continue navigate;
      }
    }
    return [];
  }
}

export function removeCollinear([...vertices]) {
  if (vertices.length < 3) {
    return vertices;
  }
  vertices.push(vertices[0]);
  vertices.push(vertices[1]);
  const trimmed = [];
  let i = 0;
  while (i < vertices.length - 2) {
    if (isCollinear(vertices[i], vertices[i + 1], vertices[i + 2])) {
      vertices.splice(i + 1, 1);
    }
    else {
      trimmed.push(vertices[i]);
      i += 1;
    }
  }
  return trimmed;
}