Atkinsonpoint – LISA Slide Show 1.0
A native slideshow tool for the Apple Lisa Office System. It appears on the LOS desktop
as its own icon, opens into a full-window carousel, and displays 680 x 300 one-bit
pictures – photographs dithered on a modern computer and delivered to the Lisa over a
serial line. Click or press a key to advance, or let it run itself at one of three speeds.
Written in Lisa Pascal with the Workshop 3.0 toolchain; runs under Lisa Office System
3.1 on real hardware.
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Why "Atkinsonpoint"
The name honors Bill Atkinson twice over, because this program depends on him twice
over.
Atkinson wrote QuickDraw, the graphics library at the heart of the Lisa and, later, the
Macintosh. Every pixel this tool puts on the screen – the window, the menus, and the
single CopyBits call that blits each slide – is drawn by his code, running where he wrote
it. QuickDraw on this machine is not a tribute or an emulation.
Atkinson also devised the dithering algorithm that bears his name: a technique for
turning grayscale photographs into pure black-and-white images that still read as
photographs. Like Floyd-Steinberg dithering, it diffuses each pixel's quantization error
to its neighbors – but Atkinson's version deliberately spreads only three quarters of the
error (one eighth to each of six neighbors, discarding the rest). Throwing part of the
error away costs some shadow and highlight detail but keeps the midtones crisp and
airy, which is exactly right for a 1-bit screen viewed at arm's length. It became the
signature look of early Macintosh imaging (MacPaint, HyperCard).
And the name is a small pun on "PowerPoint," by way of Teslerpoint (see Thanks): the
Lisa was always meant to give presentations ;)
Tom Stepleton – his Teslerpoint proved that a Lisa makes a fine slide carousel and
inspired this program. No Teslerpoint code is used here (that program is bare-metal
68000 assembly; this one is Pascal on the Office System), but the idea is his. His
lisabbs and documentation work also underpin LISACom, this tool's companion.
Alex Anderson-McLeod (alexthecat123) – his LOS Minesweeper is the template every
LOS desktop tool in this family is built from, and his LOS Compilation Base image
supplies the Workshop environment and Apple's own ICONEDIT. His LisaFPGA made
nightly testing practical.