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+Subj:  Re:  some notes
Date:  94-01-05 01:01:51 EST
From:  nathan@cco.caltech.edu
To:    AFC DYAJim
Posted on: System

Jim-
   Well, I dunno about the Softdisk problem... That's probably Zak's code; I
shared an office with him for 6 weeks this summer, so although I have a lot
of respect for his coding, sometimes he can make stupid mistakes... :)
   Well, I don't quite have my IIGS hooked up to anything but 120 vAC, and my
stereo, so the printing isn't a problem. :)
   Any thoughts on my idea of hardwiring the branches in the interrupts?
   As to the 6-sided things, well, I'll tell you my secret. It's not matrices
in the least. With my algorithm, I have one pair on the Y axis. (The first point
is always just to the right of the positive y-axis). Therefore, it's pair is
the same thing, but on the negative-y axis.
   That leaves us 4 points (they're symmetric, think about it), so what we
need to do is rotate the given (x,y) + 60 degrees clockwise. If you remember
your formulas from geometry (sin(x+y)=blah...), you'll see that:

NX=cos(30)*y+sin(30)*x
NY=sin(30)*y-cos(30)*x

   And since sin(30)=0.5, that's merely a lsr instruction. I have the hex
equivalent of cos (30) ($DDB3-- I wrote a neat HP48 program that translates
numbers <1 to hex equivalents... Want it?), and so that's merely a _Multiply.
Once I have the first point, (everything's in dx & dy from the center), I can
generate the other 4 by negating the deltas, and all. Just draw it out, it's
really simple.

   You mentioned a bit ago that you didn't get the C flame source that I sent.
Is that so, or what?

Nathan


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From: nathan@cco.caltech.edu (Nathan Mates)
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To: afcdyajim@aol.com
Subject: Re:  some notes
AOL-Member: afcdyajim