On Wed, 12 Feb 2014 11:27:12 -0800 Bill Spitzak <spit...@gmail.com> wrote:
> I think I was wrong to say the display time would always be >= to the > time the client specifies. It would be rounded just like you are > saying, the nearest start time would be rounded to the nearest output > frame start time and thus could be earlier. > > I tend to think of a "frame" as covering a period of time. Ie I don't > say it is centered at a given time, instead I tend to think of it as > *starting* at a time and having a "length". That is exactly how I think of it, a frame period begins at time P[n]. The tick of P[n] is not in the middle of a frame period, it is at the *beginning* of the frame period. The same for the T ticks, they mark the intended begin time, IOW the presentation time. > Therefore I see your > scheme as "you are required to add T/2 or you will be early". No. > I believe it would be less confusing to describe the algorithm as > start times rather than middle points, primarily because it will line It *is* described as start times. > up your 'P' points with the green lines, and because it makes it The green lines are NOT frame boundaries. The green lines give the range that gets rounded to a particular stating time P. Guess I should not have made them vertical, but triangles with the peak at the tick P[n]. > easier to talk about actual wall time (ie the client cannot do > anything about the past so this is a time that always describes a > "start"). But I also believe the result will be an identical > algorithm so if you think otherwise I don't really see a problem. > > Special effects are rather inconsistent. For sound and computed > motion, and often for motion blur they tend to think of the time > being at the start of the frame. But keyframed animation and tracking > tend to think of the time as being in the middle of a frame, > primarily because the user wants to place something at a point, and > not have to set two keys who's average is that point. All timestamps are starting times already. The only thing being at a mid-point (a green line) is where the result of the rounding switches from one P to another. - pq > Pekka Paalanen wrote: > > > Ok, so what you are suggesting here is that we should change the > > whole design to always have presentation come late with a mean > > delay of half the refresh period (T/2) and the amount of delay > > being between 0 and T. > > > > Just like you say, then the client will have to arbitrarily guess > > and subtract T/2 always to be able to target the vblank at a P. > > Also note, that since presentation feedback reports the time P, not > > P - T/2, the clients really need to do the subtraction instead of > > just queueing updates with target time t = P + n * T. _______________________________________________ wayland-devel mailing list wayland-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/wayland-devel