Find the point at which one line segment intersects another.

getSegmentSegmentIntersection.ts

function getSegmentSegmentIntersection(
  x0: number,
  y0: number,
  x1: number,
  y1: number,
  x2: number,
  y2: number,
  x3: number,
  y3: number
) {
  const denom = (y3 - y2) * (x1 - x0) - (x3 - x2) * (y1 - y0);
  const numeA = (x3 - x2) * (y0 - y2) - (y3 - y2) * (x0 - x2);
  const numeB = (x1 - x0) * (y0 - y2) - (y1 - y0) * (x0 - x2);

  if (denom === 0) {
    if (numeA === 0 && numeB === 0) {
      return undefined; // Colinear
    }
    return undefined; // Parallel
  }

  const uA = numeA / denom;
  const uB = numeB / denom;

  if (uA >= 0 && uA <= 1 && uB >= 0 && uB <= 1) {
    return [x0 + uA * (x1 - x0), y0 + uA * (y1 - y0)];
  }

  return undefined; // No intersection
}