Triangle intersection check

doTrianglesIntersect.js

// Triangle format: [[x, y], [x, y], [x, y]]

function doTrianglesIntersect(triangle1, triangle2) {
  function doEdgesIntersect(edge1, edge2) {
    // Check if two line segments (edges) intersect
    const [x1, y1] = edge1[0];
    const [x2, y2] = edge1[1];
    const [x3, y3] = edge2[0];
    const [x4, y4] = edge2[1];

    const den = (x1 - x2) * (y3 - y4) - (y1 - y2) * (x3 - x4);

    if (den === 0) {
      // Edges are parallel, no intersection
      return false;
    }

    const t = ((x1 - x3) * (y3 - y4) - (y1 - y3) * (x3 - x4)) / den;
    const u = -((x1 - x2) * (y1 - y3) - (y1 - y2) * (x1 - x3)) / den;

    return t >= 0 && t <= 1 && u >= 0 && u <= 1;
  }

  // Calculate edges for both triangles
  const edges1 = [
    [triangle1[0], triangle1[1]],
    [triangle1[1], triangle1[2]],
    [triangle1[2], triangle1[0]],
  ];

  const edges2 = [
    [triangle2[0], triangle2[1]],
    [triangle2[1], triangle2[2]],
    [triangle2[2], triangle2[0]],
  ];

  // Check for edge intersections
  for (const edge1 of edges1) {
    for (const edge2 of edges2) {
      if (doEdgesIntersect(edge1, edge2)) {
        return true; // Triangles intersect
      }
    }
  }

  return false; // Triangles do not intersect
}