AGI, which Sierra used up until around the release of King’s Quest IV – The Perils of Rosella, was a strictly linear scripting language with a fairly simple bytecode. Much simpler than SCI’s object-oriented virtual machine. But how do they compare?

Inspired by this one particular book that’s ostensibly about SCI but contains only AGI snippets from what I’ve seen, here’s the first playable room in King’s Quest IV, and how it’s initialized. I’ve left out a bunch of stuff for clarity. Because it’s so simple, AGI bytecode is pretty easy to decompile:

if (justEntered)
{
  set.horizon(84);
 
  if (!nightTime) { v152 = 1; }
  else { v152 = 101; }
  load.pic(v152);
  draw.pic(v152);
  discard.pic(v152);
 
  //Place Ego according to the previous room
  if (lastRoom == 1) { position(ego, 141, 82); }
  if (lastRoom == 2) { position(ego, 107, 82); }
  if (lastRoom == 9) { position(ego, 96, 82); }
  if (lastRoom == 10) { position(ego, 80, 82); }
  if ((lastRoom == 11 || lastRoom == 15)) { position(ego, 70, 82); }
  if ((lastRoom == 12 || lastRoom == 14)) { position(ego, 60, 82); }
 
  //Add some waves in the water.
  animate.obj(o3);
  load.view(55);
  set.view(o3, 55);
  set.loop(o3, 4);
  set.priority(o3, 5);
  ignore.objs(o3);
  cycle.time(o3, 3);
  position(o3, 64, 152);
  draw(o3);
 
  draw(ego);
  show.pic();
}

Hmm. Compare that to its SCI equivalent. SCI bytecode is much harder to decompile. You can disassemble it, but until SCI Companion came out it wasn’t possible to decompile it. Still here we are:

(instance Room1 of Room
  (properties
    picture 1
    north 25
    south 7
    west 31
    east 2
    horizon 100
  )
 
  (method (init)
    (if gNightTime (= picture 101))
    (super init:)
    (self setRegions: 503 501 504 506)
    (wave1
      isExtra: 1
      view: 665
      loop: 0
      cel: 0
      posn: 203 76
      setPri: 0
      ignoreActors:
      cycleSpeed: 3
      init:
    )
    ; Other waves left out for clarity
    (waves add: wave1 wave2 wave3)
    (wave1 setScript: waveActions)
 
    ; This part is simplified significantly.
    (switch gPreviousRoom
      (south (gEgo posn: 225 188))
      (north (gEgo x: 225 y: (+ horizon 1)))
      (0 (gEgo x: 220 y: 135))
      (east (gEgo x: 318)) ; Y stays the same.
    )
    (gEgo init:)
  )
)

You might notice that there’s no equivalent to draw.pic and discard.pic and such. The Room class handles that by itself the moment Room1 calls (super init:).