@antv/g2/src/transform/pack.ts

the Grammar of Graphics in Javascript

import { deepMix } from '@antv/util';
import { TransformComponent as TC } from '../runtime';
import { calcBBox } from '../utils/vector';

export type PackOptions = Record<string, unknown>;

function modifier(P, count, layout) {
  const pcount = P.length;
  if (pcount === 0) return [];

  // col * row >= count
  // row is close to col * aspect, so
  // col * (col * aspect) >= count
  const { innerWidth, innerHeight } = layout;
  const aspect = innerHeight / innerWidth;
  let col = Math.ceil(Math.sqrt(count / aspect));

  // Increase col to avoid total height of packed shape
  // being large than height of bbox.
  let size = innerWidth / col;
  let row = Math.ceil(count / col);
  let h0 = row * size;
  while (h0 > innerHeight) {
    col = col + 1;
    size = innerWidth / col;
    row = Math.ceil(count / col);
    h0 = row * size;
  }

  // Some offset to increase the space usage.
  const space = innerHeight - row * size;
  const intervalY = row <= 1 ? 0 : space / (row - 1);
  const [offsetX, offsetY] =
    row <= 1
      ? [(innerWidth - pcount * size) / (pcount - 1), (innerHeight - size) / 2]
      : [0, 0];

  return P.map((points, m) => {
    const [x, y, width, height] = calcBBox(points);

    const i = m % col;
    const j = Math.floor(m / col);

    const newX = i * size;
    const newY = (row - j - 1) * size + space;

    const sx = size / width;
    const sy = size / height;

    // Translate the shape and mark to make sure the center of
    // shape is overlap before and after scale transformation.
    const tx = newX - x + offsetX * i;
    const ty = newY - y - intervalY * j - offsetY;
    return `translate(${tx}, ${ty}) scale(${sx}, ${sy})`;
  });
}

/**
 * Uniform pack to avid overlap.
 * @todo Improve or change algorithm to increase space usage.
 * @todo Take some special case into account.
 */
export const Pack: TC<PackOptions> = () => {
  return (I, mark) => {
    return [I, deepMix({}, mark, { modifier, axis: false })];
  };
};

Pack.props = {};