WHATIF and Linux

Simon Andrews simon.andrews at bbsrc.ac.uk
Tue Sep 4 03:28:40 EST 2001

Michael Pachta-Nick wrote:
> Hello everybody,
> has anybody ever made it to let WhatIf run under Linux and get the 3D
> stereo mode working using stereographics hardware (emitter connected to
> 3 pin Mini DIN socket on the graphics card and Crystal Eyes Shutter
> Glasses)?
> We desperatly tried to get it work with an Elsa Gloria XXL (3DLabs Glint
> MX chipset), but no way. Linux (resp. XFree86) doesn't support this card
> very well.
> The WhatIf manual says, that you "only" have to add a modeline to your
> XF86Config which defines an interlace-mode. Unfortunatly the 3DLabs
> accelerated server doesn't support interlace.
> If anybody ever got stereoscopic view work under Linux/XFree86, what
> kind of graphics card do you have? I would be very happy to get a hint.

This is a slightly more general reply than your question about Whatif,
but I have had some experience with trying to get stereo hardware woking
under Linux.

The main thing to consider is what kind of stereo you're trying to get,
there are two kinds above-below (also called interlaced), and frame
sequential stereo.

The short story is that you should be able to get above-below stereo to
work fine under Linux, but frame sequential stereo isn't available yet
(or at least it wasn't when I tried about 6 months ago with an Elsa
Gloria II !).

Above-below stereo should work on pretty much any hardware, it doesn't
require a fancy graphics card, but it does require an external box
called a sync-doubler.  This should have been provided along with your
shutter glasses.  In your case you say you are plugging the glasses
straight into the card - this would be right for frame sequential
stereo, but you may need to buy an external sync doubler to go between
the glasses and the card for use under Linux.  All the fancy hardware
stereo capabilities of your card will probably only work under Windows
(but you'll still get a boost in render speed under Linux).

Basically what happens in above-below stereo is that the computer draws
the two stereo images on top of each other on the screen.  The sync
doubler then doubles the sync rate of the monitor so that it refreshes
twice as fast as it should.  This means that the top half of the screen
is drawn so that it fills the whole screen, then the beam returns to the
top and the bottom half of the screen is drawn to fill the whole
screen.  This continues so that the two stretched images flick back and
forth on screen (which gives you the stereo effect when viewed through
shutter glasses).

For this to work you need to check two things;

1) That your monitor can handle a refresh rate of at least 120Hz at the
resolution you are using (many monitors can't - so don't just use a
normal monitor without checking).

2) You then need to alter your XF86Config to create a display mode with
the appropriate resolution, and a refresh rate of ** 60Hz **.  This is
probably what the manual was referring to.  Since the refresh rate is
doubled when working in stereo it is important that you don't set this
any higher than 60Hz or your monitor won't handle the doubled refresh

You should just then be able to switch to stereo mode (the screen will
show two flattened images on top of each other), then turn on the sync
doubler and put on your glasses.  Bingo - stereo!

I was disheartened at the lack of Linux support for frame sequential
stereo (which is *much* better than above-below once you get it
working), but I did find several messages on developers forums
suggesting that OpenGL (emulated) stereo was in the pipeline.  Then we
just have to convince manufacturers to start writing decent Linux
drivers for their cards and everyone will be happy!

I hope that some of this helps.....



PS Seeing as you already have the card, have you tried running Swiss PDB
Viewer under windows in frame sequential stereo?  That should work like
a charm.

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