hile Bill Atkinson was developing LisaGraf, the crucial, lightning fast graphics package that was the foundation of both the Lisa and Macintosh user interface (it was renamed QuickDraw for the Mac), he also worked sporadically on a simple bitmap-based drawing program for the Lisa called SketchPad. SketchPad enabled mouse-based drawing with a selection of paintbrushes and patterns, and gave Bill a quick way to test out and show off new features or improvements as they were added to LisaGraf.In early 1983, soon after the Lisa was announced at the 1983 annual shareholders meeting, Bill switched from working on Lisa system software to writing a killer graphics application for the Macintosh. Steve Jobs thought that he should work on a structured drawing program, something like Mark Cutter’s LisaDraw, but Bill thought that structured drawing was too complex, and wanted to create something that was simple, elegant and fun to use.le Bill Atkinson was developing LisaGraf, the crucial, lightning fast graphics package that was the foundation of both the Lisa and Macintosh user interface (it was renamed QuickDraw for the Mac), he also worked sporadically on a simple bitmap-based drawing program for the Lisa called SketchPad. SketchPad enabled mouse-based drawing with a selection of paintbrushes and patterns, and gave Bill a quick way to test out and show off new features or improvements as they were added to LisaGraf.
He began by dusting off his old SketchPad code, and getting it running on the Mac as MacSketch. SketchPad used menus to select patterns and styles to draw with, but Bill replaced them with permanent palettes at the bottom of the screen and added another large, prominent palette on the left, containing a variety of drawing tools. More tools would be added over time, but the basic structure of MacPaint was there from its earliest stages.
The first big advance that Bill worked on was eliminating flicker. As you dragged a shape or image across the screen, it had to be erased from its old position before being drawn in the new one, which caused a distracting flicker as the video sometimes displayed interim, partially rendered states. Bill completely eliminated flicker by composing everything in an offscreen memory buffer, which was transferred to the screen in one fell swoop, so the interim states were never visible.
In fact, despite the Macintosh’s limited memory, he used two offscreen buffers, each the size of the document window, with one containing the current pixels of the document, and the other containing the pixels of its previous state, before the most recent operation. This made it very easy to implement undo, by just copying the old buffer to the new. It also enabled fast drawing, because it was very easy to access the original state of the document in the second buffer as an object was being modified.
