From: agodwin@acorn.co.uk (Adrian Godwin)
Subject: Re: Low end VR
Date: 7 Oct 91 12:02:12 GMT
Organization: Acorn Computers Ltd, Cambridge, UK



In article <1991Oct4.204147.7584@milton.u.washington.edu> pepke@scri1.scri.
fsu.edu (Eric Pepke) writes:

>Now, how to get the stuff in your eye?  If we use a full video board per 
>eye, we're wasting a lot of dots.  The horizontal dots get downsampled, 
>and only half the lines are shown.  Obviously one way to solve this would 
>be to go directly from bitmap to monitor without going through video, but, 
>failing that, might there be a way to have one eyepiece display only even 
>frames and the other only odd frames and drive both with a single video 
>source?

I don't know how these cheap monitors display 'half the lines', but it might
be possible to control which lines they discard by fiddling with the vertical
timing : by delaying the frame sync pulse to one of the monitors, it would
be made to display a different set of lines to that on the unmodified output.

If LCD monitors display only one of the interlaced frames (rather than 
alternate lines on the same frame) then it should be particularly easy to
generate both the multiplexed video signal and the modified timing signals.

It's rather irritating to have to generate TWO composite video signals which
differ only in their vertical sync positioning : PAL and NTSC encoders still
seem to take an inordinate number of components and board space. I'd very
much prefer to send RGB/sync or something like that straight into the display, 
if it's possible.

-adrian

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Adrian Godwin                                        (agodwin@acorn.co.uk)