Generate a nice dithered circle

dither.ts

// for any integer coordinates x, y, returns a float in [0,1] which is
// interpreted as threshold a float-valued function should have to
// reach in order to make a bitmap pixel.
function dither(x: number, y: number): number {
  return (x == 0 && y == 0
    ? 0
    : ([0, 2, 3, 1][(y % 2) * 2 + (x % 2)] + dither(x >> 1, y >> 1)) / 4);
}

function tableau(edge: number, f: (x: number, y: number) => number): number[][] {
  const table: number[][] = [...Array(edge).keys()].map(k => []);
  for (let ii = 0; ii < edge; ii++) {
    for (let jj = 0; jj < edge; jj++) {
      if (f(ii / edge, jj / edge) > dither(ii, jj))
        table[ii][jj] = 1;
    }
  }
  return table;
}

function func(x: number, y: number): number {
  return 5 * (Math.pow(x - 0.5, 2) + Math.pow(y - 0.5, 2));
}

function bitmap(edge: number): string {
  const tab = tableau(edge, func);
  let str = `P1 ${tab.length} ${tab.length}\n`;
  for (let i = 0; i < tab.length; i++) {
    for (let j = 0; j < tab.length; j++) {
      str += (tab[i][j] ? 1 : 0) + ' ';
    }
    str += '\n';
  }
  return str;
}

import * as fs from 'fs';

fs.writeFileSync('/tmp/a.pbm', bitmap(256), 'utf8');