WHATIF and Linux

Simon Andrews simon.andrews at bbsrc.ac.uk
Tue Sep 4 09:12:00 EST 2001


Michael Pachta-Nick wrote:
> 
> On Tue, 04 Sep 2001 09:28:40 +0100, Simon Andrews wrote:
> 
> Hi Simon, thank you very much for answering.
> 
> >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.
> 
> I thought that there's a difference between above/below and
> interlace, because the WhatIf manual sharply distinguishes between
> the two modes.  The WhatIf manual says concerning interlaced vs.
> above/below (chapter 59.10.2.4):
> 
> <quote>
> Actually we have started first programming this "above/below" format
> for the use of sync doublers, but later we came to the conclusion
> that the solution of stereo in a window was much better, and we
> decided to implement that one [interlace stereo] in our final
> version.
> </quote>


OK - WhatIf do seem to use Interlaced to describe frame sequential
stereo, which is not how I understand this term to be conventionally
used.  This is good in as much as frame sequential stereo is much higher
quality, and doesn't have to be full screen, but bad in terms of
soft/hardware support. 


> That seems to mean that WhatIf does not support above/below stereo
> and thus a sync doubler would be useless. Did I get that right? Or
> can I get the stereo effect without any special support by the
> software I use?

You would have to have software support for above/below stereo.  If the
above statement is the only form of stereo mentioned by Whatif then
you're stuffed I'm afraid.

 
> >Above-below stereo should work on pretty much any hardware,
> 
> But it must be supported by the software, right?

Right.

 
> >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.
> 
> Unfortunatly not. But if it would help, we'll buy it.
> 
> >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.
> 
> Actually the shutter glasses are wireless. An infrared LED emitter is
> connected to the graphics card. But that should be the same as
> attaching a pair of wired glasses to the card.


Yep.  Whether the connection is wire or IR doesn't make any difference
to how they work.

  
> When switching to stereo mode within WhatIf it draws two images of a
> molecule which are slightly shifted against each other. This is not
> what can be considered as above/below, if I got you right. So a sync
> doubler finally won't help, will it?

Really?  That sounds like what you'd expect to see from a frame
sequential display (except that the images would noticibly flicker).  I
don't know what whaif does if it can't do real stereo, but maybe it just
draws both on the same screen.  If you can get them to be different
colours (red-blue for example) then you could get stereo from coloured
glasses :-).

 
> >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.
> 
> No, but I could give it a try.

You would also have the option of above-below stereo, side by side
stereo, and even red-blue stereo.  One of those will work on any system!


Having written the original reply I went back to have a look at the
state of stereo drivers for Linux.  There seems to have been a lot of
hype that stereo support would be introduced with Xfree86 4.0, but I've
since seen a couple of posts from after this was released suggesting
that that functionality wasn't included.

The latest xfree86 (4.1) seems to have support for the hardware
acceleration in the Nvidia chips your card uses, but makes no mention of
stereo support - so I'm afraid it looks like my previous pessimism still
stands.

In fact, having just been to look at the whatif documentation at;

	http://www.cmbi.kun.nl/whatif/stereo/

The line that really seems to finish you off is;

"Because of the need to separate in time the images for each of the two
eyes, a perfect synchronisation of the glasses to the graphics hardware
is needed. This is handled in hardware by most modern graphic cards but
the appropriate software drivers to use it, for example in Linux, are
still missing." 


Try again in a few months (or switch to windows for a bit!)

	TTFN

	Simon.




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