Duken Nukem Code Review: Fully unrolled loop by Fabien Sanglard

Note: Because the code base is not using method/function is it not easy to
"unroll" the game loop the way I did it in idSoftware engines.

int main(int argc,char **argv)
{

  //Detect GRP files. check the magic number.
  load_duke3d_groupfile 

  //Detect GRP version. cache1d.c
  grpVersion = DUKEITOUTINDC_GRP
 
  //Check GRP is not corrupted.

  //CRC engine CRC, check that it has not been altered (copy protection ?).

  checkcommandline();

  copyprotect();    //Detect if CD is in CD-ROM drive (DOS only).
 
  setvmode(0x03);   //SDL call

  setmmxoverlay();

  RegisterShutdownFunction( ShutDown );

  Startup()
  {
      CONSOLE_Init
      KB_Startup
      CONFIG_GetSetupFilename
      CONFIG_ReadSetup
      compilecons
      CONTROL_Startup
      
      initengine()
      {
         loadtables
         clearbuf
         loadpalette   //Open palette.dat in the GRP file.
         {
             setpalookupaddress
             fixtransluscence
             initfastcolorlookup
         }
      }
      
      inittimer
      readsavenames
      initmultiplayers
      SetupGameButtons
      SoundStartup
      MusicStartup
      
      loadtmb
  }


  getnames

  RTS_Init(ud.rtsname);

  genspriteremaps();

  setbrightness(...);

  FX_StopAllSounds

  clearsoundlocks

  MAIN_LOOP_RESTART:

  if()
  else if(ud.warp_on == 1)
  {
     newgame()   
     enterlevel(MODE_GAME);
  }
  else 
    vscrn();


  //Finally we reach the main loop....
  while ( !(ps[myconnectindex].gm&MODE_END) ) //The whole loop!!!!!!!!!!!!!!!!!!
  {
     sampletimer();
     ...
     ...
     ...
     cheats();
     displayrooms(screenpeek,i)
     {
          dointerpolations();
          animatecamsprite();
          se40code();
          drawrooms();          //JUMP TO KEN's BUILD ENGINE
          animatesprites();     //JUMP BACK TO GAME MODULE
          drawmasks();          //JUMP TO KEN's BUILD ENGINE
     }
     displayrest(i);
     checksync();
     nextpage();                      // JUMP TO KEN's BUILD ENGINE
     {                                // It seems that "nextpage was the way to blit the new frame and pump the events from 
        _nextpage                     // the operating system.
        {
           _handle_events
        }
     }
  }
}


It seems the engine starts by drawing in the sector the player is. (pp->cursectnum).
Now the questions are:

Q: How is cursectnum set ?

Q: How does the engine finds out where the player sector is in ?

Q: How does the engine knows when to stop ?

Q: How does the engine knows how to sort walls ?