Shape table

Shape tables were a powerful yet little-used feature of Applesoft BASIC allowing for simple graphic manipulation on Apple II series computers, using the "hi-res" graphics mode.

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 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 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 did create a shape table editing program which eliminated the "number crunching" called Apple Mechanic.

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 as Applesoft shape tables).

See also

* Sprite

External links

* [http://www.atariarchives.org/cgp/Ch03_Sec05.php Atariarchives.org example] , detailed instructions on assembling shape tables by hand