Investigating MacPaint’s Source Code
Jeffrey Starr (via Stephen Hackett):
One of two launch applications for the Apple Macintosh in 1984, MacPaint is emblematic of the Macintosh’s early quirky revolutionary branding, focus on ease of use, and appeal to artistic customers. Using the source code, we examine the design and implementation of the application. We find that the buffer management and bucket filling algorithms demonstrate mechanical empathy with the 68k platform and leverage the limitations of the domain as a means to improve performance. We also find positive and negative aspects in the code style and architecture and its pliability for change. Finally, we dispute some claimed novel aspects of the program while also arguing for its significance and impact on the development of digital graphic systems.
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Atkinson took Polaroids of the user interface as it evolved and drove into work to share them with the team. Fortunately for posterity, Atkinson saved the Polaroids and we have a detailed visual history of the evolution of the Lisa interface and QuickDraw capabilities as shown in the 2022 CHM interview below.
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The Macintosh team used the ‘Monkey’ as a durability and robustness test mechanism. Developed by Steve Capps, the Monkey would randomly type keys, move objects, and interact with menus (Atkinson 2010, pg 14-15). The team used a computer running in Monkey mode to effectively stress-test an application. MacPaint was able to survive two weeks without crashing.
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Performance-critical code, such as that which manipulates the buffers directly, is in assembly. User interface control logic is in Pascal, as well as code that handles initial setup or rare operations. Operating system calls, such as checking the amount of spare space in the disk drive or invoking the system beep, are in assembly.
I am asking friends and well-wishers to pray for me. I believe that group intention can actually make a difference.
On October first, I was diagnosed with pancreatic cancer. Because of vascular involvement, surgery is not possible. I am taking weekly chemo treatments to shrink the tumor before surgical resection.
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