Thanks for the info Dennis, I'll take a look at your paper too. Just surprised the latency can be that much, but it really explains why glGet's are quite so awful!
Bruce On Jun 28, 2010, at 11:38 AM, Bunfield, Dennis AMRDEC/AEgis wrote: > Classification: UNCLASSIFIED > Caveats: FOUO > > Yes we found this through internal testing. Nvidia later confirmed it. > This isn't related to double or triple buffering either. The pipeline > as explained to me is similar to a break line in a car. Everything > works well unless you inject an air bubble into the brake line. This > would be similar to doing certain glGet's commands. The driver will tell > the GPU to stop it's processing so that it can handle your glGet > request. So for real-time programming you really need to be aware of > this -- and don't do it --. Depending upon the type of readback you are > performing you will introduce a momentary lag in the system because the > GPU has to stop everything it is doing to respond back to you. > glReadPixels behaves a little differently as long as the pixel format > aligns with the frame buffer format where the driver can just dma that > framebuffer back to the cpu. If your pixel formats are not aligned you > will get bad performance again, because the GPU will have to stop what > it is doing and reformat the data to send back. > > > -----Original Message----- > From: osg-users-boun...@lists.openscenegraph.org > [mailto:osg-users-boun...@lists.openscenegraph.org] On Behalf Of Bruce > Wheaton > Sent: Monday, June 28, 2010 12:46 PM > To: OpenSceneGraph Users > Subject: Re: [osg-users] OSG and vsync (UNCLASSIFIED) > > On Jun 23, 2010, at 3:35 PM, Bunfield, Dennis AMRDEC/AEgis wrote: > >> For Nvidia cards there is a built in 2 frames of latency. So even > after >> your sync you won't see the image you updated come out the DVI until 2 >> render frames later. > > Where does this information come from Dennis? Where is this delay > happening? I doubt it's triple buffering, since the extra memory would > have to be accounted for, and it makes tearing mostly impossible (as on > the Mac). > > So you believe the Gl command queue is buffered/delayed somewhere? > Doesn't that have huge implications for things like glGet, making them > impossible to use without at least halving the frame rate? > > Bruce > > > > > _______________________________________________ > osg-users mailing list > osg-users@lists.openscenegraph.org > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.or > g > Classification: UNCLASSIFIED > Caveats: FOUO > > > _______________________________________________ > osg-users mailing list > osg-users@lists.openscenegraph.org > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
