[Development] Qt 'minimal' platform no rendering alpha/opacity.

[Paul Knopf]

What do you mean when you say "compositor"? Are you referring to a window
system?

Is this something that is possible to implement with the minimal project?
What would have to change?

I have need a custom platform that encodes the ARGB (proprietary, vendor
specific) to the linux framebuffer, but the alpha channel has to actually
be correct.

How come I can do this without a compositor?

    QImage bitmap(widget.size(), QImage::Format_ARGB32);

    bitmap.fill(Qt::transparent);

    QPainter painter(&bitmap);

    widget.render(&painter, QPoint(), QRegion(), QWidget::DrawChildren);

    bitmap.save("file.png");


There must be a way to achieve the same result using a platform plugin.

If all else fails, I could create my own thread loop that renders the
QWidget with the above code and outputs it to my driver manually, instead
of going through the platform plugins, but I would like to support the
platform plugin so that I can then switch it out to develop locally using
standard Qt platforms (X11, etc).

On Fri, Apr 17, 2015 at 10:32 AM, Agocs Laszlo <
laszlo.agocs at theqtcompany.com> wrote:

>  You do have alpha because the minimal's backingstore uses
> ARGB32_Premultiplied for the backing QImage.
>
>  What you do not have is setWindowOpacity(). You would need to implement
> QPlatformWindow::setOpacity() for that, but that is not possible with
> minimal since there is no compositor that could apply the opacity to the
> window contents during the composition step.
>
>  Best regards,
> Laszlo
>
>   From: Paul Knopf <theonlylawislove at gmail.com>
> Date: Friday 17 April 2015 16:20
> To: "development at qt-project.org" <development at qt-project.org>
> Subject: [Development] Qt 'minimal' platform no rendering alpha/opacity.
>
>   I am testing the 'minimal' platform (mine is based off of it), and it
> seems that is doesn't render the alpha channel (setting opacity).
>
>  Here is a gist <https://gist.github.com/anonymous/544e84fbcde5022a6878> of
> my main function testing the opacity.
>
>  The saved images seems to have a tan background and no transparency.
>
>  Any ideas on how to get the alpha channel represented in the platform
> backing store?
>
>  --
> Thanks!
>
> ~Paul
>



-- 
Thanks!

~Paul
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