I'll just chip in one quick thought. On Jan 24, 2014 6:32 AM, "Pekka Paalanen" <ppaala...@gmail.com> wrote: > > Hi, > > I am investigating what kind of Wayland protocol extensions would be > needed to support proper presentation timing. Looking at existing > works, I am wondering about two things whether they have any real use. > > Where is swap interval (e.g. eglSwapInterval) greater than one useful? > Intervals 0 and 1 I understand, and Mesa EGL Wayland already supports > those. But when would you like to make your framerate a fraction of the > display's? > > When are the target-MSC related remainder and divisor parameters as > defined in the GLX_OML_sync_control useful? Why does also X11 Present > protocol include remainder and divisor? > > GLX_OML_sync_control defines that for interlaced displays MSC is > incremented for each field. With divisor and remainder you could then > target only top or bottom fields. Is that useful, and do we care about > interlaced displays anymore?
I think we do. In particular, we should care about TV set-top boxes. Even though most TVs are LCD, DLP, or similar, hdmi does support interlacing and it is still used (particularly in HDTV). I have no idea what implications this has for a present extension, but I think we could still handle it in a sane way without going for MSC. > I am contemplating on not supporting these, because I am going to > propose using an UST-like clock as the "standard clock language" in > Wayland present extension. Supporting MSC-based timings would add > complexity. Therefore I would like to know where and how the above > mentioned are useful, because I cannot imagine it myself. > > Please, let me know of real actual use cases and existing software, > where these features offer a visible benefit and what that benefit is > exactly. I am not interested in what one might do in theory, I am > interested in real-world examples where they have proved useful. Well, > maybe also theories if they allow taking advantage of some new cool > technology. > > Btw. if you think that using UST for presentation timing and feedback > is nonsense, and MSC is the only right way, let me know and I can start > another email thread about that detail after preparing my material. > > > Thanks, > pq I hope that's helpful, --Jason Ekstrand
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