It wasn't really "ported", is was developed on NeXTStep, but the target was X86/VGA/DOS"
Apparently they just cross-compiled it. Also, the NeXTStep version of Doom didn't have sound.
"We wrote all of DOOM and Quake's code on NeXTSTEP. We debugged the code in NeXTSTEP with DOOM and Quake's 320x200 VGA screen drawing in a little Interceptor window while the rest of the screen was used for debugging code. When all the code ran without bugs we cross-compiled it for the Intel processor on NeXTSTEP then turned over to our Intel DOS computers, copied the EXE and just ran the game. The DOS4GW DOS-Extender loaded up and the game ran. It was that easy."
In case, like me, you wondered what an "Interceptor window" was:
"NeXT also have an internal kit called Interceptor Kit, which allows a privileged application to punch a hole through the Postscript windowserver directly to the display card."
Apparently they just cross-compiled it. Also, the NeXTStep version of Doom didn't have sound.
"We wrote all of DOOM and Quake's code on NeXTSTEP. We debugged the code in NeXTSTEP with DOOM and Quake's 320x200 VGA screen drawing in a little Interceptor window while the rest of the screen was used for debugging code. When all the code ran without bugs we cross-compiled it for the Intel processor on NeXTSTEP then turned over to our Intel DOS computers, copied the EXE and just ran the game. The DOS4GW DOS-Extender loaded up and the game ran. It was that easy."
http://web.archive.org/web/20140310124554/http://rome.ro/200...