by Darius Kazemi, July 9 2019
Even more graphics description
The technical content
This RFC describes how a DEC PDP-10 is connected to a remote IMLAC PDS-1 vector display. It's a display system that operates in a few modes: it can support the display of text strings at any position on the screen, it can simuate a teletype by doing line feeds and carriage return type layout (like a terminal screen), and it can move back and forth between these modes.
The system uses a mouse for control. The computer mouse is still pretty rare at this point (light pens and tablets are more common at ARPANET host sites) but if anyone is going to have a mouse, it's Xerox PARC, as they were a relatively early and enthusiastic adopter of the device. (Their Xerox Alto would go on to be the first personal computer designed around mouse input.)
The various system calls are documented in a really interesting prosaic format. For instance:
If first byte pointer is zero then if a new string is being written then an error code illstr is returned. Otherwise, the string already exists so delete the string from the display area. If the first byte pointer is -1 then if a new string is being written then an error code illstr is returned. Otherwise, use the old string. If the first character of the string is a zero character, the string to be displayed is null, but the string is not deleted.
I love that each system call not only has its basic functionality described, but use cases and notes for each system call are also listed.
The system calls are somewhat similar to previous graphical display languages we've seen, wherein display areas are defined, cursors are positioned, etc.
L Peter Deutsch had a long programming career and among other things is the primary author of GhostScript, but is now primarily a composer. He's interviewed in the popular book Coders at Work by Peter Seibel.
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I'm Darius Kazemi. I'm an independent technologist and artist. I do a lot of work on the decentralized web with ActivityPub, including a Node.js reference implementation, an RSS-to-ActivityPub converter, and a fork of Mastodon, called Hometown. You can support my work via my Patreon.