Bresenham Line Algorithm

 BBS: Inland Empire Archive
Date: 07-29-92 (05:27)             Number: 184
From: RICHARD VANHOUTEN            Refer#: NONE
  To: BRIAN DESSENT                 Recvd: NO  
Subj: Bresenham Line Algorithm       Conf: (1) 80xxx

 >  BD> I also have source for an all-integer math circle drawing routine...

 > YES!  I want it too!  I have sort of made my own, except I can't
 > seem to make it work the proper dots per size etc..  THANKS!

 BD> Okay, again, this isn't asm, so I apologize for being off topic, but
 BD> maybe someone can translate this into ASM and post it :-)
 BD> circle (int xc, yc, radius)   ; center coordinates, radius

 BD> int x, y, d

 BD> x = 0
 BD> y = radius
 BD> d = 2 * (1 - radius)
 BD> while y > x
 BD> plot dot at (xc + x, yc + y)  ; I think there's only 4, but
 BD> plot dot at (xc - x, yc + y)  ; there may be 8 plotdot routines
 BD> plot dot at (xc + x, yc - y)
 BD> plot dot at (xc - x, yc - y)
plot dot at (xc + y, yc + x)
plot dot at (xc - y, yc + x)
plot dot at (xc + y, yc - x)
plot dot at (xc - y, yc - x)
 BD> if d + y > 0 then
 BD> y = y + 1
 BD> d = d - 2 * y + 1
 BD> endif
 BD> if x > d then
 BD> x = x + 1
 BD> d = d + 2 * x + 1
 BD> endif
 BD> endwhile
 BD> done

I believe the above algorithm is also credited to Bresenham.  It works with
square pixels.  If your pixels aren't square, you'll need to use a different
algorithm.



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