Tools

Mark's own 6502, written once for both machines: a run-length packer and unpacker, line drawing, circle drawing, and LZW compression, which he wrote from the pseudocode in an article in Dr. Dobb's Journal. Goldfields' title screen is a packed picture, drawn by its unpacker.

I wrote my tools and graphics library once, and used them on two machines that looked nothing alike. Their disks, memory and screens were all different, but the lines and fills, and the compression, packed and LZW, ran the same on both.Mark Wharton, 2026

Mark's work alone: he designed the engine and wrote all of it in 6502, and he wrote the vector editor the pictures were drawn in, which is not on the disks.

A picture is a named list of shapes, each a fill colour, an outline colour and its points, on the 140 by 192 double hi-res screen. The engine fills each shape by counting where its edges cross each row and filling between the crossings in pairs, then outlines it.

A driver, in 6502, for the Concept Keyboard, the flat overlay tablet used in special education. It finds the keyboard's interface card by its slot, on the IIe and the IIgs, by watching its status tick and its data hold still.

Through Applesoft's ampersand it takes a key from the keyboard or a press from the tablet, read as a cell of 128 and turned into the key the program expects by a table that is the overlay itself.