Yes the rendering code is in Delphi too. It uses an OpenGL control i wrote some years ago[0] which include OpenGL bindings for Delphi 2 (i haven't tested later versions). The control is actually a conversion of one i made for Borland C++ Builder [1].

It is not QuArK, though AFAIK QuArK was made in Delphi too. There have been a few other Quake editors made in Delphi, like the qED Quake Editor which was one of the earlier Quake editors (the author wrote a book about quake mapping too[2]).

[0] http://runtimeterror.com/tech/dglvp/

[1] http://runtimeterror.com/tech/bcbgl/

[2] https://archive.org/details/unofficial-quake-level-design-ha...