SCI Engine

The Sierra Creative Interpreter (SCI) replaced AGI as the system behind Sierra’s adventures from King’s Quest IV (1988). Sierra described it to its own customers, in the newsletter that became InterAction, as “an object-oriented language similar to LISP; it’s written in Assembler, C, and itself”, and Roberta Williams called it “a virtual machine language which means that it will work on any machine”. Games were built once in SCI and run by a separate interpreter for each machine: MS-DOS first, then Atari ST, Amiga and Macintosh — but never the Apple II or IIGS, which Ken Williams said were too slow for it.

Fast facts

Developer: Sierra On-Line.
First game: King’s Quest IV: The Perils of Rosella (1988) — “Sierra’s first SCI release”, with Police Quest II, Leisure Suit Larry II and Space Quest III “not far behind”.
Resolution: 320×200, “double the graphics resolution of previous Sierra adventures”.
Sound: IBM’s eight-voice music card, AdLib and the Roland MT-32 for King’s Quest IV; ten sound cards by Code-Name: Iceman (1990).
Interface: typed parser at first, with “more ‘point and click’ interaction” added by 1990; then an icon bar in place of the parser, which Roberta Williams says she designed.
Recognition: SPA nomination for technical achievement for SCI, and for sound for King’s Quest IV (1989).

What SCI is

Sierra’s Spring 1989 newsletter walked readers through how room 7 of King’s Quest IV — the fisherman’s shack — was built. The programmer “puts all the rooms and animated characters together to make the game run” in SCI, in which “the programmer established classes of objects. The Actor Class, for example, includes anything that moves such as sea gulls, ogres, and Ego. The Props Class is composed of items that move but don’t go anywhere — like a candle flame or smoke. The Views Class is for things that don’t require any animation.” Scripts “define how the objects come together and interact with one another”; the article prints the nine calls that make the chimney smoke, from animate.obj( smoke) to draw( smoke).

Roberta Williams gave START the origin in 1990: Ken Williams “wanted to write a special language that just did graphic adventure games, one that we could use over and over”. Because SCI was a virtual machine, “each machine format has its own version of SCI”, and the ST’s could use effects like fading that the IBM’s could not.

Rooms, views and priority bands

The same article describes the tools and data. Backgrounds were drawn in a Picture Editor and “not stored as a completed picture; instead, they’re constructed and stored as coordinates and vectors”, because vectors “take less space than would a bit image”. Characters were drawn as pixels in a View Editor, with a designated invisible colour, and animated as cycles of cells: 76 drawings for the fisherman, “more than one thousand” for Ego. Depth came from “16 bands or areas in which things may be placed”, used by the artist “like a horizontal grid”, and control lines set where Ego could walk — placed badly, “Ego will walk right through” a tree. A room averaged 12,000 to 14,000 bytes, and the artist economised where it ran over.

King’s Quest IV and the first wave

Sierra launched SCI as a line of “technologically superior interactive movies, complete with stereo soundtracks, fully animated cartoon sequences and double the graphics resolution”, with a 32-voice MT-32 score by William Goldstein. Ken Williams later called it “a big gamble”. Reviewers picked up the resolution: Computer Gaming World found Police Quest II had “doubled the graphic resolution” and added “zoom shots, split screens and film wipes”, with characters “no longer virtual stick figures”. The other cost was speed — on a PCjr “it takes an animated character almost 23 seconds to move across the screen in King’s Quest IV”.

Ports

SCI moved machine by machine. The ST versions of Space Quest III, King’s Quest IV, Police Quest II, Silpheed and Leisure Suit Larry II were listed in early 1989; the Amiga conversion ran “over six months behind schedule” and shipped Space Quest III in October 1989; Macintosh development delayed Sierra’s helicopter simulator. The Apple IIGS got none of it: SCI was “just too big and too complex for the relatively slow CPU”, so Manhunter: San Francisco, built in AGI, was expected to be the last IIGS adventure.

From parser to icons

SCI began with a parser — START praised Larry II’s “fairly sophisticated parser” — and gained “more ‘point and click’ interaction” by Code-Name: Iceman. Then Sierra removed typing altogether. In the Spring 1992 InterAction, Ken Williams called the change “much discussed” and put it to two designers. Al Lowe “didn’t like the icon interface at first” but came to prefer it: “less verbage = more puzzles”. Roberta Williams: “since I designed the icon interface I would be in favor of it … most people don’t want to take the time to learn either how to type, spell, or figure out just how you talk to a computer via an adventure game! I designed the icon interface with the future in mind … especially as it relates to fancy CD-Rom based entertainment machines.” Computer Gaming World’s hall of fame later credited King’s Quest V (1990) with redefining “the graphic adventure with new parser and VGA graphics”. See point and click for the wider shift.

Sierra's Creative Interpreter