Function SimpleTriangulation

Common/DataModel/vtkPolygon.cxx:1385–1602

------------------------------------------------------------------------------ Handles some trivial triangulation cases. Returns 0 if cannot triangulate the current polygon. 3 and 4 points are handled with special care for concave quad.

// Handles some trivial triangulation cases. Returns 0 if cannot triangulate
// the current polygon. 3 and 4 points are handled with special care for concave quad.
int SimpleTriangulation(vtkIdList* ptIds, vtkPoints* pts, double tol2, vtkIdList* tris)
{
  int number_of_verts = ptIds->GetNumberOfIds();
  // Just output the single triangle
  if (number_of_verts == 3)
  {
    double x0[3], x1[3], x2[3];
    bool valid = true;
    pts->GetPoint(0, x0);
    pts->GetPoint(1, x1);
    pts->GetPoint(2, x2);
    if (vtkMath::Distance2BetweenPoints(x0, x1) < tol2 ||
      vtkMath::Distance2BetweenPoints(x1, x2) < tol2 ||
      vtkMath::Distance2BetweenPoints(x0, x2) < tol2)
    {
      valid = false;
    }
    if (valid)
    {
      tris->SetNumberOfIds(3);
      std::iota(tris->begin(), tris->end(), 0);
      return 1;
    }
  }

  // Four points are split into two triangles. Watch out for the
  // concave case (i.e., quad looks like a arrowhead).
  else if (number_of_verts == 4)
  {
    // There are only two ear cutting possibility.
    // This boolean
    bool use_d1 = true;
    bool concave = false;
    // Temporary storage of the four points
    double x0[3], x1[3], x2[3], x3[3];
    // Quad possible diagonals with d1 and d2
    double d1[3], d2[3];
    // complementary vector to analyse fan
    double v1[3], v3[3];
    // face normal
    double normal[3];
    // local tri normal
    double n1[3], n2[3];
    double area;

    pts->GetPoint(0, x0);
    pts->GetPoint(1, x1);
    pts->GetPoint(2, x2);
    pts->GetPoint(3, x3);
    // Build diagonals for ear cutting
    d1[0] = x2[0] - x0[0];
    d1[1] = x2[1] - x0[1];
    d1[2] = x2[2] - x0[2];
    //
    d2[0] = x3[0] - x1[0];
    d2[1] = x3[1] - x1[1];
    d2[2] = x3[2] - x1[2];