Method IntersectWithLine

Common/DataModel/vtkBox.cxx:432–525

------------------------------------------------------------------------------ Bounding box intersection code from David Gobbi. Go through the bounding planes one at a time and compute the parametric coordinate of each intersection.

// bounding planes one at a time and compute the parametric coordinate
// of each intersection.
int vtkBox::IntersectWithLine(const double bounds[6], const double p1[3], const double p2[3],
  double& t1, double& t2, double x1[3], double x2[3], int& plane1, int& plane2)
{
  plane1 = -1;
  plane2 = -1;
  t1 = 0.0;
  t2 = 1.0;

  for (int j = 0; j < 3; j++)
  {
    for (int k = 0; k < 2; k++)
    {
      // Compute distances of p1 and p2 from the plane along the plane normal
      int i = 2 * j + k;
      double d1 = (bounds[i] - p1[j]) * (1 - 2 * k);
      double d2 = (bounds[i] - p2[j]) * (1 - 2 * k);

      // If both distances are positive, both points are outside
      if (d1 > 0 && d2 > 0)
      {
        return 0;
      }
      // If one of the distances is positive, the line crosses the plane
      else if (d1 > 0 || d2 > 0)
      {
        // Compute fractional distance "t" of the crossing between p1 & p2
        double t = 0.0;
        if (d1 != 0)
        {
          t = d1 / (d1 - d2);
        }

        // If point p1 was clipped, adjust t1
        if (d1 > 0)
        {
          if (t >= t1)
          {
            t1 = t;
            plane1 = i;
          }
        }
        // else point p2 was clipped, so adjust t2
        else
        {
          if (t <= t2)
          {
            t2 = t;
            plane2 = i;
          }
        }

        // If this happens, there's no line left
        if (t1 > t2)
        {
          // Allow for planes that are coincident or slightly inverted
          if (plane1 < 0 || plane2 < 0 || (plane1 >> 1) != (plane2 >> 1))
          {
            return 0;