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Path: utzoo!utgpu!utcsri!uthub!ecf!drascic
From: drascic@ecf.UUCP
Newsgroups: comp.sys.amiga
Subject: Swapping graphics pages at 60Hz
Message-ID: <187@mv05.ecf.toronto.edu>
Date: Fri, 3-Jul-87 14:28:44 EDT
Article-I.D.: mv05.187
Posted: Fri Jul  3 14:28:44 1987
Date-Received: Sat, 4-Jul-87 16:58:26 EDT
Organization: Engineering Computing Facility, University of Toronto
Lines: 46
Keywords: stereographics, video signals, graphics buffers

SUMMARY: (question from a novice)
    Does the Amiga have the capability of creating separate graphics
    pages which can be swapped at a rate of 60 Hz, in sync with the
    video display?

I am considering purchasing an Amiga in order to overlay computer
graphics on a video image.  But I'm not working with just ordinary
video and graphics: I'm working in 3D stereoscopic video.

The method I'm using involves alternating views.  I have liquid
crystal shutters that block of the view of first the right, and then
the left, eye.  By presenting left and right eye views on the screen
at a fast enough rate, the illusion of depth is given.

The standard 30 Hz interlaced NTSC video signal presents 30 frames per
second. But if the frames were drawn in the obvious way, all the lines
from top to bottom, 30 times per second, the resultant image would
flicker in an annoying way.  Instead, each frame is split into EVEN
lines (2,4,6,etc.) and ODD lines, thus creating two slightly
different pictures with half the resolution.  All of the even lines
are drawn first, from top to bottom, followed by all of the odd
lines.  This results in a 60 Hz flicker, which is much less noticeable.

In order to generate our stereo display, we use the EVEN lines for the
left view, and the ODD lines for the light view.  These two views
come from different cameras.  What we want to do is use the Amiga to
draw dynamic three dimensional, "stereo" images in the same way.  We will
thus need two graphics buffers, and we will need to be able to switch
between these 60 times a second, in sync with the screen refresh.  Is
this possible?  Is it amazingly difficult?  I know the Atari can
do it, since they are marketing similar glasses with software.  But
we need to overlay the graphics on a video signal, and thus can
use the Amiga's genlock board.  This makes the Amiga more suitable for
our needs, provided that it can do stereoscopic animation.

Since we want to do simple animation, it seems to me that we will need
4 graphics buffers:  two for the current left and right views, and
two in which to draw the new left and right views.  This will prevent
the drawing of the new image from being seen.  If we were only drawing
a simple, 3D wireframe cube, would this be necessary?  If so, can it
be done?

Thanks.

	David Drascic.
	  drascic@utecfb    OR    drascic@ecf.toronto.edu