MacPaint’s Downloadable Source Shows How Bill Atkinson Hid the Flicker

The picture was finished before the screen saw it. Atkinson composed graphics in a hidden memory buffer, then copied the completed result to the display. That avoided the visible erase-and-redraw sequence as objects moved.

The museum’s release page lets readers go beyond the anecdote: MacPaint 1.3 has 5,822 lines of Pascal and another 3,583 lines of assembly. QuickDraw, the underlying graphics library, has its own source download.

The museum labels the material “only for non-commercial use.” Downloadable history comes with conditions; a source-code archive is not automatically an open-source license.

The same attention to what people saw could become a little controlling. In “Desk Ornaments,” Andy Hertzfeld recalls adding a desktop pattern editor that let owners make their own backgrounds. Atkinson objected: the patterns could be ugly, and he did not want them visible around MacPaint. His solution was to have the application cover the desktop with its own standard gray background. You could customize the room; MacPaint would bring a curtain.

Hertzfeld favored letting owners do what they wanted, since they could return to a built-in pattern. In one case, Atkinson concealed an unfinished drawing operation. In the other, he concealed a finished choice the owner had deliberately made. A smooth experience and control over that experience can pull in different directions, even inside a drawing program.

MacPaint also helped shape tools beyond its own window. Hertzfeld’s “Steve Icon” account says its Fat Bits mode inspired the icon editor he made for Susan Kare. That editor enlarged a 32-by-32 grid while keeping a small actual-size view alongside it. A designer could work on individual dots without losing sight of the face those dots had to become.

Kare made a recognizable Steve Jobs portrait inside that tiny grid. Atkinson then sat with her while she made his portrait, which went into MacPaint’s About box. The man hiding intermediate pixels still wanted his own finished pixels in the program. Hertzfeld recalls other teammates requesting portraits too, until being drawn by Kare became a status symbol. Hertzfeld calls it “a Mac team status symbol.”

The museum also describes a character-recognition feature Atkinson removed because he wanted a good drawing program, rather than an inadequate word processor. Even the feature that never shipped has something to contribute to today’s overloaded app menu.

A historical source release can make design decisions available for examination long after the machine leaves the desk. The interesting next step is tracing one familiar interaction through the code and seeing which compromises still sound familiar.