Typescript implementation of the Bresenham Line-Drawing Algorithm using generators

bresenham-line-algorithm.ts

/* Iterate integer points on a line where dx >= dy and x0 <= x1. */
function *iter_line_low(
  [x0, y0]: [number, number],
  [x1, y1]: [number, number]
): Generator<[number, number], void, unknown> {
  const dx = x1 - x0;
  const dy = y1 - y0;

  let y = y0;
  let e = 0;

  if (dy === 0) {
    for (let x = x0; x <= x1; x++) {
      yield [x, y];
    }
  }
  else if (dy > 0) {
    for (let x = x0; x <= x1; x++) {
      yield [x, y];
      e += dy;
      if ((e << 1) >= dx) {
        y += 1;
        e -= dx;
      }
    }
  }
  else {
    for (let x = x0; x <= x1; x++) {
      yield [x, y];
      e += dy;
      if ((e << 1) <= -dx) {
        y -= 1;
        e += dx;
      }
    }
  }
}

/* Iterate integer points on a line where dy >= dx and y0 <= y1. */
function *iter_line_high(
  [x0, y0]: [number, number],
  [x1, y1]: [number, number]
): Generator<[number, number], void, unknown> {
  const dx = x1 - x0;
  const dy = y1 - y0;

  let x = x0;
  let e = 0;

  if (dx === 0) {
    for (let y = y0; y <= y1; y++) {
      yield [x, y];
    }
  }
  else if (dx > 0) {
    for (let y = y0; y <= y1; y++) {
      yield [x, y];
      e += dx;
      if ((e << 1) >= dy) {
        x += 1;
        e -= dy;
      }
    }
  }
  else {
    for (let y = y0; y <= y1; y++) {
      yield [x, y];
      e += dx;
      if ((e << 1) <= -dy) {
        x -= 1;
        e += dy;
      }
    }
  }
}

/* Iterate integer points on a line. Input points *must* be comprised of integers. */
function iter_line(
  p0: [number, number],
  p1: [number, number]
): Generator<[number, number], void, unknown> {
  if (Math.abs(p0[0] - p1[0]) >= Math.abs(p0[1] - p1[1])) {
    return p0[0] <= p1[0]
      ? iter_line_low(p0, p1)
      : iter_line_low(p1, p0);
  } else {
    return p0[1] <= p1[1]
      ? iter_line_high(p0, p1)
      : iter_line_high(p1, p0);
  }
}