[vlc-devel] Display update/restart

[Steve Lhomme]

On 2020-11-16 17:11, Alexandre Janniaux wrote:
> Hi,
> 
> On Mon, Nov 16, 2020 at 05:01:29PM +0100, Steve Lhomme wrote:
>> On 2020-11-16 16:08, Thomas Guillem wrote:
>>> Indeed, the more important, glitch-wise, is to keep the window enabled.
>>>
>>> Can we stop and start the 3 main vouts (gl, d3d9, d3d11) without any glitches? Even when changing the video size for example ?
>>
>>  From what I understood at least on iOS the background becomes white if you
>> remove the display module. But that's probably not hard to fix.
> 
> This might be tuned to keep the previous surface as long as we
> don't disable the window or have a new surface to render. I'm
> not sure it can be turned into glitch free though but we could
> try.

If the surface belongs to the display module it will be gone when the 
display is released.

>> The issue is not the glitch. It's how long it's going to take to unload a
>> display module and reload it, for a tiny change that would take almost no
>> time to handle directly.
> 
> We should measure it. Shader recompilation is an issue but we
> might workaround it with shader caching. Some platforms already
> have transparent caching for this.

There's a persistent cache even after the display module is released ?

>> The other issue, already mentioned in another email, is that the detection
>> of format change is done on picture.next, not picture.current. So we would
>> not display picture.current if we close the display when picture.next is
>> just loaded.
>>
>> And there's also the question of getting picture.next from the deinterlacer.
>> There's no way to put it back in the filter for the next display to get it.
>>
>> In short, it's a giant mess to handle with the current code.
> 
> I think it's more about defining the policy to make sense
> of the mess, than handle this mess before. ;)

Yes.

Another important topic is filter draining. For example if you switch 
from interlacing to non interlacing you don't just unload the filters, 
you have to tell them to keep outputting pictures with no input pictures 
until it's all dry. Only then you can switch to the non interlaced 
filter chain(s).

> Regards,
> --
> Alexandre Janniaux
> Videolabs
> 
>>> On Mon, Nov 16, 2020, at 16:04, Rémi Denis-Courmont wrote:
>>>> Le lundi 16 novembre 2020, 13:24:33 EET Steve Lhomme a écrit :
>>>>> One of the last missing part in push is the possibility to
>>>>> update/restart the display module when the source changes. A corollary
>>>>> of this is when we decide to use a converter filter or not.
>>>>
>>>> We covered that in the last related workshop. In the push model, there's no
>>>> point reusing the display anymore, since it won't cause problems with the
>>>> picture pool, and it won't glitch the window.
>>>>
>>>> You can just make a new one. In other words, this is a non-issue.
>>>>
>>>> --
>>>> Rémi Denis-Courmont
>>>>
>>>>
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