Re: Channel viewpoint stepping
Angus Dorbie (dorbie++at++sgi.com)
Tue, 21 Apr 1998 14:53:09 -0700
Jean-Luc Dery wrote:
>
> Hi people,
>
> We are having problems with the way the channel viewpoint is being updated. Our
> channel viewpoint steps every time the channel frame rate drops from 60Hz to
> 30Hz due to scene complexity. This happens only during the transitions. We are
> quite sure that the problem comes from the way the channel viewpoint is managed
> within our Performer based application since when frame rate is stable (30Hz or
> 60Hz), the viewpoint movements are perfectly fluid. The problem occurs only
> when the frame rate changes. The value used for the viewpoint setting is
> computed and updated in a parallele process which always runs at 60Hz.
>
> Is the channel viewpoint set in the APP from pfChannel API frame conherent in
> the 3 stage APP CULL DRAW pipeline? I would suspect so since the pfChannel is a
> libpf object.
>
> When the frame rate drops at frame 5 (D3) in the phase lock mode
>
> frame 1 2 3 4 5 6 7
> APP A1 | A2 | A3 | A4 | A5 | A6 | A7
> CULL | C1 | C2 | C3 | C4 | C5 | C6
> DRAW | | D1 | D2 | D3.|. | D5
>
> Is the viewpoint used to draw at frame 7 (D5) really set from A5 ?
>
> How can we guaranty channel viewpoint fluid movement, or what could we be doing
> wrong that could cause the stepping in our application. Is there a need to
> interpolate viewpoint when frame rate changes.
>
> Thanks in advance for any help,
>
Unless you know you're goind to miss your frame rate it's too late to do
anything.
I mean you've started to draw if you don't make the vertical retrace
then the
old image will be preserved and the currently rendered image will arrive
late.
In the mean time the application could still be updating depending on
phase ,
and this is as it should be so eventually when you make frame rate again
your
eye point will catch up.
Cheers,Angus.
--
"Only the mediocre are always at their best." -- Jean Giraudoux
For advanced 3D graphics Performer + OpenGL based examples and tutors:
http://www.dorbie.com/
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on Mon Aug 10 1998 - 17:57:17 PDT