Penumbra and HPL2

[Hannibal]

So you can take the HPL1 engine source and make it even better them HPL2 if you want.

Clearly, the developers of HPL thought it was faster/easier to achieve the HPL2 featureset by writing HPL2 from scratch rather than to update the HPL1 engine. Usually when we discuss engines, we're discussing what they can do for us out-of-the-box, now what they could possibly potentially do if everything were re-written or severely modified. Well, except for the special case of engines that do not release the source code.