[vlc-devel] [PATCH 3/3] snapshot: fix copy of opaque pictures

[Rémi Denis-Courmont]

Le maanantaina 5. kesäkuuta 2017, 18.54.17 EEST Thomas Guillem a écrit :
> > > This will create issues with some hardwares.
> > 
> > No. The picture context has always had reference counting internally. It
> > just
> > was never exposed to the core.
> > 
> > In other words, a back-end without reference counting can´t use the
> > picture
> > context trick. And it has always been but a trick to make up for the lack
> > of
> > converter, filter and splitter pools.
> 
> Ok but why no ?

Why what???

> How do you prevent the vout and a filter to use the same
> context for display/reading at the same time ?

I don´t understand what that´s supposed to mean. The core has no means to know 
or enforce those constraints, even as things already stand without snapshot 
support. Synchronized access is a concern for the back-end to deal with, and 
it would likely cause notable performance degradation already with decoder and 
renderer running in separate threads.

If however the back-end really can only consume a picture only once at all (as 
opposed to once at a time), snapshot would require synchronous copy to CPU, 
then a copy back to GPU in a new identical picture for rendering. I would 
argue that such a back-end should never be enabled by default and is not worth 
supporting snapshot for.

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