[Interest] Draw a qimage with transparency on a QOpenGLPaintDevice
maitai
maitai at virtual-winds.org
Mon May 2 11:37:02 CEST 2022
Hi,
I discovered that it does not behave always like that. It happens only
when painting very quickly many small QImages with transparent areas.
And I found a way to fix it, but this is just adding mystery.
Instead of
pnt->drawImage(etc);
I do
pnt.beginNativePainting();
pnt.endNativePainting();
pnt->drawImage(etc);
This seems to force a kind of flush and all is fine after that.
Should I report a bug?
Thanks
Philippe
Le 01-05-2022 13:45, maitai a écrit :
> Hi,
>
> I have some heavy rendering that I would like to speed up using openGL.
> For the time being using only QPainter regular method but later some
> native openGL code.
>
> So instead of painting on a QImage, I am painting on a
> QOpenGLPaintDevice. All is fine except one point: When the painter
> draws a QImage containing alpha, these alpha pixels appear black.
> CompositionMode is QPainter::CompositionMode_SourceOver and QImage
> format for the source is QImage::Format_ARGB32_Premultiplied. Same code
> painting in a QImage works fine.
>
> I have tried to glEnable(GL_BLEND) and glEnable(GL_DEPTH_TEST) and some
> others but that didn't fix the issue.
>
> Any idea of what needs to be done ?
>
> Many thanks in advance
>
> Philippe Lelong
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