[vlc-devel] [PATCH] video_output: wait half the extra time we have without getting the display_lock

[Steve Lhomme]

This is more a workaround than a clean solution.

In an ideal world we would never wait between prepare and display, they 
would have predictable time and we could estimate exactly when we must 
do the prepare to be on-time for the display.

That would also leave all that time to the vout control loop to process 
more mouse events that might occur before we start the displaying.

Looking at how we handle the deadline in Windows, it seems we sometimes 
missing the deadline by too far and we end up having to skip the frame 
we wanted to display (with its deadline) because now we won't have 
enough time to render it in time.

On 2021-02-19 12:16, Steve Lhomme wrote:
> Since f1bf7ce5b4480a3d38d54c7ae1d1564f0670d83f we start the rendering much
> earlier than before, so we have more time to do things if necessary.
> 
> The problem is that for almost all the duration of the call display_lock is
> held. So it's blocking all other UI related events from being handled. Even if
> we are going to spend most of the time waiting until we can do the display.
> 
> This patch waits a bit before locking the display_lock when we estimate we will
> have so extra time before doing the display/swap.
> 
> Fixes #25479
> ---
>   src/video_output/video_output.c | 17 +++++++++++++++++
>   1 file changed, 17 insertions(+)
> 
> diff --git a/src/video_output/video_output.c b/src/video_output/video_output.c
> index d04d3f4d111..c176c274334 100644
> --- a/src/video_output/video_output.c
> +++ b/src/video_output/video_output.c
> @@ -1119,6 +1119,23 @@ static int ThreadDisplayRenderPicture(vout_thread_sys_t *vout, bool render_now)
>       if (filtered->date != sys->displayed.current->date)
>           msg_Warn(&vout->obj, "Unsupported timestamp modifications done by chain_interactive");
>   
> +    if (!render_now)
> +    {
> +        vlc_tick_t now = vlc_tick_now();
> +        vlc_tick_t system_pts = vlc_clock_ConvertToSystem(sys->clock, now, filtered->date, sys->rate);
> +        if (unlikely(system_pts != INT64_MAX))
> +        {
> +            const vlc_tick_t late = now - system_pts;
> +            if (unlikely(late <= 0))
> +            {
> +                // wait half the extra time we have without the display_lock
> +                vlc_tick_t max_time_to_render = sys->render.avg;
> +                vlc_clock_Wait(sys->clock, now , filtered->date - max_time_to_render / 2, sys->rate,
> +                            VOUT_REDISPLAY_DELAY);
> +            }
> +        }
> +    }
> +
>       vout_display_t *vd = sys->display;
>   
>       vlc_mutex_lock(&sys->display_lock);
> -- 
> 2.29.2
> 
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