From: Dan Johnston (dan.johnston++at++nrc.ca)
Date: 12/17/2001 09:48:38
brad schwagler wrote:
> When I load large models using the stereo example
> provided by the performer examples, there is a
> dramatic
> FPS drop. Using Perfly the models are displayed at a
> high FPS. What does perfly do differently than the
> stereo example?
Think about what quad-buffered stereo means. In
normal (double bufferd) display mode for Performer
apps, including perfly, the computer is 'drawing' into
the back buffer while the monitor is 'showing' the
front. When (pf)draw is finished, the hardware
does a 'swap buffers'.
In quad-buffered mode, the system maintains a
front and back set of separate right and left
buffers (hence the name). You have to (pf)draw
into the back left, and then draw the same
scene with the eye-to-eye channel offset
into the right back buffer. So drawing time
is ~doubled.
The the computer monitor/projector must render
the both channels. The standard (now) is to
use 'field sequencial' video formats. This means
that you first render the left eye view, then you
pause briefly, and the render the right eye view.
Very fast stereo uses 120Hz. which gives you
60Hz per eye. Many displays require that you
slow the rendering down to fit the limits of
the monitor/projector. Rates of 48 to 57Hz
per eye are common. So your visual may be
slower.
(The above paragraph does not apply to
passive stereo display systems).
Hope this helps. You will expect at least
half the frame rate of an identical non-stereo
software/hardware system. I have software
where I can toggle to/from active stereo
display. No other change in hardware, software
or model viewpoint. The 'half mono rate'
approximation is always close.
> I've tried using DVR, different
> threads, phase runs, etc. Nothing seems to chop down
> the
> draw process.
Unless you can split the draw process, or get faster
hardware to support the draw, then the rate will
not change.
> Also,I've noticed that models slow the
> program down even when they're hidden.
What do you mean ... 'hidden'? If a large part
of a very complex model is deleted or out of
the view frustum then the draw time will be
less. If the geometry is transparent, then it
(draw time) may actually be more. If the
geometry is just behind some other piece
of geometry (and still in the view frustum)
the the draw time will not change because
Performer will STILL DRAW THE
HIDDEN GEOMETRY. It will not be
'hidden' until the z-buffer sorting (which
is just about the last stage).
> Any ideas,
> and if so, are there any examples online? ...Thanks
>
--
___|__ |
/ | \ ||\ Daniel (Dan) Johnston
/___|___\ || \ Dan.Johnston++at++nrc.ca
_____|____ || \ National Research Council of Canada, London, ON
| | | || \ Integrated Manufacturing Technologies Institute
\___| | | ||____\ Tel: (519) 430-7081 Fax: (519) 430-7090
\_o_\___|____|_|______\_ Inst: http://www.nrc.ca/imti
\ o / These opinions are my own! Not those of NRC.
\________________/ Virtual Reality:
http://www.nrc.ca/imti/vetc/home.html
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