Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!cbmehq!cbmger!peterk
From: peterk@cbmger.UUCP (Peter Kittel GERMANY)
Newsgroups: comp.sys.amiga.tech
Subject: Fast circles?
Keywords: Circles, fast, Blitter
Message-ID: <656@cbmger.UUCP>
Date: 20 Dec 90 12:03:10 GMT
Organization: Commodore Bueromaschinen GmbH, West Germany
Lines: 61


Here a question for a little project I perhaps would like to
continue during the holidays:

I want to draw FAST, filled circles in arbitrary size and in
arbitrary (but solid) color on a 4-bitplane hires screen.
You see, I still love these first-day Caleidoscope demos and
want to do similar things on my own.

BTW: These Caleidoscope demos had an announcement in their
opening screen that this was only a demo for a real, coming
product by Electronic Arts with which you were said to be able
to create all such effects on your own. But this product never
made it to the public. I already wrote to EA whether they could
let me the source for it but got no answer. Anyone existing
with better connections to them?

So I was left on my own. I already achieved some
nice line art effects, also solid area things, but my current
attempts with circles are not very satisfying.
So: what strategy is optimal?

1. Is AreaEllipse() simply the best? (I tried it, see above.)
2. I already tried to make up my own 32-edge polygon and draw
   it with AreaDraw()/AreaEnd. I would prefer to find a faster
   solution.
3. Would it be better to manage the 4 bitplanes separately by
   hand in an own loop? Which Blitter commands would be 
   appropriate for this from C?
   One advantage in this special situation is that the objects
   have solid color. Thus the mask for any cookie-cutting has
   the same shape in every bitplane as the object itself, it
   only has to be inverted for some (or null) of the bitplanes.
   I imagine a single bitmap set aside which holds a one-bitplane
   circle and its inverted image and using this as sources for
   all the Blitter operations. Perhaps I can make this bitplane
   a little bigger providing space for circles and masks of
   many different sizes so that they only need to be computed
   one single time at start.
   Hmm, do I really need that inverted circle image? Isn't this
   inversion already done by simply using the proper minterms
   for the Blitter? (You see, I'm no expert in this, ... yet :-)
4. To avoid flickering, I think about syncing the drawing with
   WaitTOF(). If one circle is too big to get drawn fully during
   one vertical scan (I assume this program runs alone on the
   machine, NO multitasking, pure demo as fast as possible),
   then I think about cutting the circle in two halfs (or even
   more parts) so that the eye perhaps may follow the drawing
   process but sees no color flickering resulting from incomplete
   bitmaps.
5. Would it be necessary to turn to assembler to gain further
   performance?

Well, if some kind soul may enlighten me or simply point me to
the proper place in the RKMs...

Have a nice Christmas and a happy plus successfull new year!

-- 
Best regards, Dr. Peter Kittel  // E-Mail to  \\  Only my personal opinions... 
Commodore Frankfurt, Germany  \X/ {uunet|pyramid|rutgers}!cbmvax!cbmger!peterk