[vlc-devel] [PATCH] [RFC] picture: use the offset to increase the visible lines/pitch

[Steve Lhomme]

On Thu, Sep 10, 2015 at 6:26 PM, Rémi Denis-Courmont <remi at remlab.net> wrote:
> Le 2015-09-10 19:19, Steve Lhomme a écrit :
>>
>> On Thu, Sep 10, 2015 at 5:55 PM, Rémi Denis-Courmont <remi at remlab.net>
>> wrote:
>>>
>>> Le 2015-09-10 18:50, Steve Lhomme a écrit :
>>>>
>>>>
>>>> Since we don't use the x/y offset when copying planes (plane_t is
>>>> missing
>>>> these fields), we may miss some pixels.
>>>
>>>
>>>
>>> So?
>>
>>
>> So it's missing some pixels that should be displayed.
>
>
> I got that, but I don't get how that justifies corrupting the visible lines
> count and pitch.
>
>> Either we add
>> the offset information in plane_t (unlikely as we need to check all
>> the code using plane_t).
>
>
> I agree that would be impractical. But...
>
>> Or we consider the offset adds a visible area.
>
>
> That corrupts used values. It breaks some video outputs. I am not sure if it
> does not also break some filters.

I don't see how that corrupts anything. It would be a problem if we
modified i_lines and i_pitch. Because we would read/write on areas we
shouldn't. The 'visible' variants are there for optimizations. If
anything, more data are copied/handled. But I don't see how anything
would become corrupt with this change.

>> It should be safe as it only applies to plane_t data when
>> manipulating pixels.
>
>
> I don't see how that could be safe, unless the values were not used at all
> (in which case, removing them would have been the obvious solution).
>
>
> --
> Rémi Denis-Courmont
> http://www.remlab.net/
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