Get the intersection of two rays.

readme.md

Demo: https://codesandbox.io/s/intersection-of-two-rays-mcwst

getRaysIntersection.ts

/**
 * Get the intersection of two rays, with origin points p0 and p1, and direction vectors n0 and n1.
 * @param p0 The origin point of the first ray
 * @param n0 The direction vector of the first ray
 * @param p1 The origin point of the second ray
 * @param n1 The direction vector of the second ray
 * @returns
 */
export function getRaysIntersection(
  p0: number[],
  n0: number[],
  p1: number[],
  n1: number[]
): number[] | undefined {
  const dx = p1[0] - p0[0];
  const dy = p1[1] - p0[1];
  const det = n1[0] * n0[1] - n1[1] * n0[0];
  const u = (dy * n1[0] - dx * n1[1]) / det;
  const v = (dy * n0[0] - dx * n0[1]) / det;
  if (u < 0 || v < 0) return undefined; // Might intersect as lines, but not as rays.

  const m0 = n0[1] / n0[0];
  const m1 = n1[1] / n1[0];
  const b0 = p0[1] - m0 * p0[0];
  const b1 = p1[1] - m1 * p1[0];
  const x = (b1 - b0) / (m0 - m1);
  const y = m0 * x + b0;

  return Number.isFinite(x) ? [x, y] : undefined;
}

Probably useful too: a helper to get a normalized direction vector between two points.

function getDirectionVector(x0: number, y0: number, x1: number, y1: number) {
  const dx = x1 - x0
  const dy = y1 - y0
  const l = Math.hypot(dy, dx)
  return [dx / l, dy / l]
}