docs: function lineIntersects(line1StartX, line1StartY, line1EndX, line1EndY, line2StartX, line2StartY, line2EndX, line2EndY) {
    // if the lines intersect, the result contains the x and y of the intersection (treating the lines as infinite) and booleans for whether line segment 1 or line segment 2 contain the point
    var denominator, a, b, numerator1, numerator2,
      result = {
        x: null,
        y: null,
        onLine1: false,
        onLine2: false
      };
    denominator = ((line2EndY - line2StartY) * (line1EndX - line1StartX)) - ((line2EndX - line2StartX) * (line1EndY - line1StartY));
    if (denominator === 0) {
      if (result.x !== null && result.y !== null) {
        return result;
      } else {
        return false;
      }
    }
    a = line1StartY - line2StartY;
    b = line1StartX - line2StartX;
    numerator1 = ((line2EndX - line2StartX) * a) - ((line2EndY - line2StartY) * b);
    numerator2 = ((line1EndX - line1StartX) * a) - ((line1EndY - line1StartY) * b);
    a = numerator1 / denominator;
    b = numerator2 / denominator;
  
    // if we cast these lines infinitely in both directions, they intersect here:
    result.x = line1StartX + (a * (line1EndX - line1StartX));
    result.y = line1StartY + (a * (line1EndY - line1StartY));
  
    // if line1 is a segment and line2 is infinite, they intersect if:
    if (a > 0 && a < 1) {
      result.onLine1 = true;
    }
    // if line2 is a segment and line1 is infinite, they intersect if:
    if (b > 0 && b < 1) {
      result.onLine2 = true;
    }
    // if line1 and line2 are segments, they intersect if both of the above are true
    if (result.onLine1 && result.onLine2) {
      return [result.x, result.y];
    } else {
      return false;
    }
  }