A Hack on the Wild Slide

Tom Becker

Yes, I was there. The Wednesday Night Hack-Off. They filled the room, munching brownies and quaffing caffeine-laced beverages. No, I can't give you any names. They're OOF hackers. Object Oriented Frameworks. Plenty of class, but no hierarchy. They were there, trying out the latest tools. Cranking code until sunrise. Hacking digital data structures into analog engines of computation: the original GUI calculator. Slide rule with a Daystar accelerator.

The spec. It was hand drawn. Just one sheet hot off the copier. It was crude. It was vague. It was factually incorrect. Yes, I wrote it. You got a problem? We didn't want anything to impede the hacker's raw creativity. Besides, this exercise was supposed to be realistic.

I walked in about 8 or so, after the Alger Memorial Pizza Feed. The hacker's den was already hopping. I already knew what I wanted to try: Get started with AppMaker to draw the GUI and generate TCL code. Finish with the fast turnaround times of THINK C.

Started working in a whirlwind of effort. Wait a minute. Things were missing. We're not in AppMaker any more, Toto. Was this alpha code or what? Ran out into the hallway and grabbed Spec Bowers. (At the Frameworks Conference, support is never far away.) He wanted to know how I liked the prototype. It was great, but there was a slide rule waiting for me.

Quickly dropping down a level of abstraction, I copied the starter project from the TCL demos. Renamed the files. Now I had a working app with a window. Time to draw some things. The copy of THINK Reference installed on the machine didn't include the toolbox reference or TCL. Fortunately, most of the toolbox functions I needed were in QuickDraw.h, and there was a printed TCL reference. Created a pane class for each part of the slide rule. Became very familiar with the TCL reference. Created a mouse task subclass to drag the slide. Found a disabled superview that was keeping clicks from getting to the slider. Enabled it. Dragging the slide worked. Undo worked. Added a mouse task to drag the indicator. Tried to remember how to draw logarithmic scales. At this point, I was half done; ready to work on cosmetic issues. Got smooth dragging of the indicator using XOR. Biggest problem was how to control TCL view focus/clipping. Couldn't drag the slide from within a mouse task without flickering. Got it working sort of OK by 6 AM. It was time. Slapped an icon on and shipped it.

Never used TCL before, but no problemo. Anyone with several years of MacApp experience can get up to speed right away. Another big advantage: the quick turnaround times with THINK C. I could make mistakes a lot faster. Experiment and let the compiler check it. Real interactive programming.

Back home, I dug up my copy of An Easy Introduction to the Slide Rule. Isaac Asimov, 1965. "A slide rule," he says, "doesn't seem as impressive as a giant electronic computer, but it has many advantages. It is small enough to put in your pocket, it need not cost more than a couple of dollars, it can't go out of order, and, best of all, it can solve almost any numerical problem that you meet up with under ordinary circumstances. To add to all that, it is simple to operate." Right on.