Translucent background - repaint issue Mac

SGaist

When a patch gets and added and removed it generally means that it breaks something while trying to fix something else

Talei

I suspected that it's the case in this situation.

In general, as person that is new to MacOoX world, does it means that we cant get translucent background window?

Maybe there is a wok around this? Native window?

SGaist

Yes you can but your exact use case triggers that bug. One things you can do however is to add information on the current bug reports (also vote for it).

Talei

So how would I go about getting translucent background for widget in Qt on Mac?

SGaist

You already are using it, but why did you disable the background auto fill ?

Talei

For TransWidget it was for testing - don't change anything

On qlabel - I want only text no bg from QLabel, but that doesn't change the fat that if autoFill is true then rectangle is "left behind" and when false actual text.

sandy.martel

I the same problem on Mac when moving from Qt4 to Qt5. I could reproduce it with different projects or code examples. I fixed it by adding this code to my application:

@
void MyTransparentWindow::paintEvent( QPaintEvent * /event/ )
{
QPainter p( this );

// Qt5 fail to give us a clear backbuffer...
p.setCompositionMode( QPainter::CompositionMode_Clear );
p.fillRect( 0, 0, width(), height(), QColor( 0, 0, 0, 0 ) );
p.setCompositionMode( QPainter::CompositionMode_SourceOver );
// end

...
}
@

This fixed the problem for me when using Qt5.1.1, I haven't check if it's actually fixed in Qt5.2+.

Talei

sandy.martel
THANK YOU

I experimented earlier with fill Qt::transparent but without composition mode. Setting (only)

@
void TransWidget::paintEvent( QPaintEvent * /event/ )
{
QPainter p( this );

p.setCompositionMode( QPainter::CompositionMode_Clear );
p.fillRect( this->rect(), Qt::transparent );

}
@

resolves problem:

Qt 5.2.1 - MacOSX 10.9.2

SGaist

Very nice trick !

Thanks for sharing :)

JakeW

Thanks a lot for the trick, it works for me!

Dzybba

This topic is old, but i face with same problem and tricks won't help me. Im using Qt 5.5
So i found solution in Telegram app source code.

Set attributes and window flags
m_widget->setWindowFlags(Qt::FramelessWindowHint | Qt::BypassWindowManagerHint | Qt::Tool | Qt::NoDropShadowWindowHint);
m_widget->setAttribute(Qt::WA_NoSystemBackground, true);
m_widget->setAttribute(Qt::WA_TranslucentBackground, true);
In paint event
QPainter::CompositionMode m = painter.compositionMode();
painter.setCompositionMode(QPainter::CompositionMode_Source);
painter.setOpacity(0.4);
painter.fillRect(w->rect(), Qt::black);
painter.setCompositionMode(m);