Display PostScript

~ the obit ~

Display PostScript shipped in 1987 onto machines that cost about as much as a car. The installed base was university computer labs and the kind of finance desk that bought a workstation per seat, so my distance from this one is just arithmetic. It was already being replaced by the time I got a 14.4k modem, and no screen I had ever sat in front of had been drawn by it.

The problem it solved is worth stating precisely, because it sounds trivial now and was not. PostScript was written for printers. Its model was one document at a time, broken into pages, with instructions piling up until a showpage command arrived and the whole lot was executed and then thrown away. A screen works nothing like that. There is no final page and drawing has to happen immediately, and several windows may be drawing at the same moment with completely different settings. So Adobe and NeXT added multiple execution contexts: each window got its own PostScript interpreter state and its own stack, independent or shared as the programmer liked, plus a tool called pswrap that generated C functions from PostScript fragments so ordinary application code could call them.

What you got for that was one imaging model from the screen to the paper. The same language that described the printed page described the window, which meant a document on screen was the document that would come out of the printer, down to the curves. NeXT licensed it in September 1987, the first company to do so, and wrote an entire new windowing engine around it. Digital Equipment licensed it in early 1988 for DECwindows. In January 1988 Adobe was publicly pressing Apple and IBM to adopt it too, with OS/2's Presentation Manager named as the target.

NeXTSTEP is where it went deepest. The titlebars and the scrollers were drawn in PostScript, wrapped in objects and handed to the programmer as objects, so the whole interface was made of the same stuff as the content inside it. Sun held out with its own PostScript-based window system, NeWS, until OpenWindows 3.3 in November 1993, which dropped NeWS and its nonstandard extensions and switched to DPS.

~ the rap sheet ~

~ why apple dropped it ~

Apple bought NeXT in 1997 and inherited an operating system whose entire display layer was licensed from Adobe. The NeXT-derived releases kept it, and then Mac OS X did not. Apple wrote its own window server, which caches window contents as bitmaps rather than storing and re-executing drawing code, and built a graphics library called Quartz 2D on the PDF imaging model, which is most of PostScript's model minus the programming language around it.

Two reasons are usually given and both hold. There was no licensing fee to Adobe for an imaging model Apple implemented itself. And Mac OS X had to run a decade of existing Macintosh software whose drawing was all QuickDraw bitmaps, which fits a compositing bitmap server far better than it fits a PostScript interpreter. By the time 10.0 shipped in March 2001 there was no PostScript anywhere near the screen.

~ what got buried with it ~

Applications written against DPS lost their foundation, which in practice meant the NeXT-era creative tools and the one-off visual experiments that had drawn straight into a PostScript context. Interface Builder layouts from that era describe windows in terms of a rendering system that no longer exists under them. None of it was dramatic, because the installed base was small and had already been migrating for years, but it is the reason a certain class of early nineties workstation software cannot simply be recompiled.

~ the rise, inverted ~

The strange part of the story is that DPS lost while its idea won. Every mainstream desktop now composites resolution-independent vector graphics with the same drawing model from screen to print, which is precisely what Display PostScript was built to do in 1987. What did not survive was the decision to make that model a full programming language with an interpreter in the window server. PDF, which is PostScript with the loops and the variables taken out, turned out to be the version everyone wanted, and Adobe won anyway on the format while losing the engine.

@}-->--

              )
             (_)
            .-'-.
            |   |
            |   |
            |   |
            |   |
          __|   |__   .-.
       .-'  |   |  `-:   :
      :     `---'     :-'
       `-._       _.-'
           '""""""

« previous  ·  random  ·  next »