code: private boolean addTangents(Grid grid, int rowA, int colA, int rowB, int colB) {
  		EllipseRotated_F64 a = grid.get(rowA,colA);
  		EllipseRotated_F64 b = grid.get(rowB,colB);
  
  		if( a == null || b == null ) {
  			return false;
  		}
  
  		if( !tangentFinder.process(a,b, A0, A1, A2, A3, B0, B1, B2, B3) ) {
  			return false;
  		}
  		Tangents ta = tangents.get(grid.getIndexOfHexEllipse(rowA,colA));
  		Tangents tb = tangents.get(grid.getIndexOfHexEllipse(rowB,colB));
  
  		// add tangent points from the two lines which do not cross the center line
  		ta.grow().set(A0);
  		ta.grow().set(A3);
  
  		tb.grow().set(B0);
  		tb.grow().set(B3);
  		return true;
  	}
docs: Computes tangent points to the two ellipses specified by the grid coordinates