Hi,
I am porting existing Qt4-based code to Qt5 (5.5.0), switching from
QGLWidget to QOpenGLWidget. In my app I render a bunch of text and
bitmaps into a transparent QImage. The QImage is then alpha-blended in
OpenGL on top of video frame (rendered with OpenGL with texture buffer
originating from ffmpeg libraries).
I've observed an artifact after the switch to QOpenGLWidget. It appears
as if rendering anti-aliased text to a transparent buffer blends a white
background color into the text outline -- see attached screenshots. It
should be red background, black outline, gray text. What I get is red
background, whitish anti-aliasing (or alpha-blending) halo around black
outline, black outline, and gray text.
I don't think the problem is with QPainter::drawText, because I see the
same whitish halo around bitmap subtitles which I render into the same
transparent QImage via QPainter::drawImage. Also, if I use QGLWidget as
the base class the issue vanishes -- the anti-aliasing halo only appears
when using QOpenGLWidget.
Is this a bug, or some secret setting I missed?
Thank you,
Pavel.
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