I actually have Doom3 like surfaces in the game (at least a very basic variant of it - I wanted to make whole minigames with it- but in the end it only got used for the screen on the E4 boss .. btw do you plan on a full playthrough? I'm starting to wonder if I actually included episode 3 onward - everyone seems reluctant to go beyond 2 🤔)
HL is strange like that.. as I recall they bought both the Q1 and Q2 engine then mushed the source codes together
and replaced an excellent OpenGL renderer with some DirectX bullshit (cuz' they were still microsoft at heart I guess 🫠)