VclPtr<VirtualDevice> attribute in the OutputDevice class

[Tomaž Vajngerl]

Hi Adrien,

On Tue, Nov 12, 2019 at 7:54 AM Adrien Ollier <adr.ollier at hotmail.fr> wrote:

> Hello everybody,
>
>
> In the /core/include/vcl/outdev.hxx file, at line 331 we can see the
> attribute mpAlphaVDev which is of type VclPtr<VirtualDevice>. And the
> comment at line 330 is "TEMP TEMP TEMP".
>
>
That's one of those permanent temporary variables that was intended to be
removed in a week, but is still in the code after a decade.


> Does someone know what this attribute is for?
>
>
It's for the alpha channel of the VirtualDevice to make the it support
transparency.


> Using opengrok, when I search for mpAlphaVDev
> (https://opengrok.libreoffice.org/s?refs=mpAlphaVDev&project=core), I
> see that the pointer is created when the OutputDevice is a VirtualDevice
> (in /core/vcl/source/gdi/virdev.cxx at line 367), and I couldn't find
> any other line where mpAlphaVDev is instanciated.
>

Instantiated in one place, yes, but it is used all over OutputDevice
drawing code.

Can someone confirm this? If that is true, at least the attribute should
> be moved in the VirtualDevice class. But I can't understand the reason
> to be of this attribute. Should not it be purely and simply removed?
>

No, we can't just remove it just yet. The code needs to be changed so it
supports native alpha of our backend surfaces, but that's quite a lot of
very careful work. I'm writing various tests in VCL just so this could be
safely implemented without breaking anything.

What could be removed is that "TEMP TEMP TEMP" comment.

Best regards,
>
> Adrien Ollie


Best Regards,
Tomaž Vajngerl
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