Method ProjectTo2D

Common/DataModel/vtkTriangle.cxx:922–954

------------------------------------------------------------------------------ Project triangle defined in 3D to 2D coordinates. Returns 0 if degenerate triangle; non-zero value otherwise. Input points are x1->x3; output 2D points are v1->v3.

// triangle; non-zero value otherwise. Input points are x1->x3; output 2D
// points are v1->v3.
int vtkTriangle::ProjectTo2D(const double x1[3], const double x2[3], const double x3[3],
  double v1[2], double v2[2], double v3[2])
{
  double n[3], v21[3], v31[3], v[3];

  // Get normal for triangle
  vtkTriangle::ComputeNormal(x1, x2, x3, n);

  for (int i = 0; i < 3; i++)
  {
    v21[i] = x2[i] - x1[i];
    v31[i] = x3[i] - x1[i];
  }

  double xLen = vtkMath::Normalize(v21);
  if (xLen <= 0.0)
  {
    return 0;
  }

  // The first point is at (0,0); the next at (xLen,0); compute the other
  // point relative to the first two.
  v1[0] = v1[1] = 0.0;
  v2[0] = xLen;
  v2[1] = 0.0;

  vtkMath::Cross(n, v21, v);

  v3[0] = vtkMath::Dot(v31, v21);
  v3[1] = vtkMath::Dot(v31, v);

  return 1;
}

//------------------------------------------------------------------------------
// Support triangle clipping. Note that the table defines triangles (three ids