Shape tables are a feature of the
Apple II
The Apple II (stylized as ) is an 8-bit home computer and one of the world's first highly successful mass-produced microcomputer products. It was designed primarily by Steve Wozniak; Jerry Manock developed the design of Apple II's foam-m ...
ROMs which allows for manipulation of small images encoded as a series of vectors. An image (or ''shape'') can be drawn in the high-resolution graphics mode—with scaling and rotation—via software routines in the ROM. Shape tables were supported via
Applesoft BASIC and from machine code in the "Programmer's Aid" package that was bundled with the original
Integer BASIC
Integer BASIC is a BASIC interpreter written by Steve Wozniak for the Apple I and Apple II computers. Originally available on cassette for the Apple I in 1976, then included in ROM on the Apple II from its release in 1977, it was the first version ...
ROMs for that computer.
Applesoft's high-resolution graphics routines were not optimized for speed,
so shape tables were not typically used for performance-critical software such as games, which were typically written in assembly language and used pre-shifted bitmap shapes. Shape tables were used primarily for static shapes and sometimes for fancy text; Beagle Bros offered a number of fonts in ''Font Mechanic'' as Applesoft shape tables.
Technical details
The
vectors of a two-dimensional graphic, each encoding a direction from the previous pixel along with a flag indicating whether the new pixel should be illuminated or not, were encoded up to three in a byte. These were stored in a table via the Monitor or the
POKE command. From there, the graphic could be referenced by number (a table could contain up to 255 shapes), and built-in Applesoft routines permitted scaling, rotating, and drawing or erasing the shape. An
XOR
Exclusive or or exclusive disjunction is a logical operation that is true if and only if its arguments differ (one is true, the other is false).
It is symbolized by the prefix operator J and by the infix operators XOR ( or ), EOR, EXOR, , ...
mode was also available to allow the shape to be visible on any color background; this had the advantage, also, of allowing the shape to be easily erased by redrawing it.
Apple did not provide any utilities for creating shape tables; they had to be created by hand, usually by plotting on graph paper, then calculating the hexadecimal values and entering them into the computer.
Beagle Bros
Beagle Bros was an American software company that specialized in creating personal computing products. Their primary focus was on the Apple II family of computers. Although they ceased business in 1991, owner Mark Simonsen permitted the Beagle Bro ...
created a shape table editing program, which eliminated the "number crunching", called ''
Apple Mechanic'', and a related program, ''
Font Mechanic''.
See also
*
Sprite
References
{{reflist
External links
Atariarchives.org example detailed instructions on assembling shape tables by hand
Computer graphics