Re: Stats Question correction
Rémi Arnaud (remi++at++remi.engr.sgi.com)
Mon, 6 Apr 1998 16:41:42 -0700 (PDT)
Angus Dorbie wrote:
>
> Marcus Barnes wrote:
> >
> > On Apr 6, 11:46am, Jay Gischer wrote:
> > >The label "frame" appears to be causing a great deal of confusion
> > >here. Recall the picture of Performer's pipe
> > >
> > >APP | Frame 1 | Frame 2 | Frame 3 | Frame 4 | etc
> > >
> > >CULL | | Frame 1 | Frame 2 | Frame 3 | etc
> > >
> > >DRAW | | | Frame 1 | Frame 2 | etc
> > >
> > >If 30.0 Hz is the target frame rate then the target from one pipe
> > >stage boundary to the next is 33.3 ms.
> > >
> > >However, the time reported with the label "frame" is a latency time,
> > >and measures the time from when the frame starts the APP stage, to
> > >when it completes the draw stage. Ignoring special cases, this time
> > >is 3 times as long as the time for a single stage. Three time 33.3 is
> > >100, so 96.3 is about right.
> >
> > I don't believe that this timeline takes the video refresh period into account.
> > Recall that the draw is double buffered. Therefore you don't actually see the
> > results of the draw process for another "video frame". This adds to your
> > latency.
> >
>
> This is incorrect. The vertical line is the vertical retrace. When the
> draw ends it swaps and the image is switched at the next vertical
> retrace,
> in the diagram this is the line at the end of draw. Almost immediately
> thereafter the video starts getting sent on the wire without any video
> buffering and should begin to appear on your screen if you use CRTs.
> There are different schools of thought on where latency should be
> measured to. Some say the beginning of video, others say the end
> but it has little to do with the I.G. You say potato I say potato.
It is often added as 1/2 frame of latency. I guess this is from the
ages where IG and projector were unable to provide non-interlaced
video.
>
> 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 - 17:57:13 PDT