semi-transparent window with a visible line on it

[nagpalma]

Hi to all and good to be here!

I'm using Qt 4.2.3 on Windows XP and i'm trying to do a semi-transparent principal window drawing a simple line on it, changing the paintEvent of the Qwidget.
I don't want that line to be transparent. I used setWindowOpacity(0.0) but the line on it becames also tranparent.
How can i achieve my goal?

Any help would be appreciated.
Thanks,

nagpalma

[marcel]

In paintEvent(). where you draw the line, use painter->setOpacity( 1.0f ) before you draw the line and after you draw the line restore the original opacity.

Regards

[nagpalma]

Hi marcel,

it didn't solve the problem
I'm using the fowlling code:

#include <QtGui>
 
#include "transparent.h"
 
Transparent::Transparent(QWidget *parent)
     : QWidget(parent, Qt::FramelessWindowHint)
 {
     setWindowTitle(tr("Transparent Window"));
     setWindowOpacity(0.0);
 }
 
 
     //window.resize(400, 400);  
 
     //window.setFixedSize(500,500);
     //window.showMaximized();
 
 
 void Transparent::paintEvent(QPaintEvent *)
 {
   QPainter p(this);
   p.setOpacity(1.0);
   p.drawLine(0, 0, 50, 50);        // drawing code
   p.setOpacity(0.0);
 }
 
 QSize Transparent::sizeHint() const
 {
     return QSize(400, 400);
 }

#include <QtGui>
 
#include "transparent.h"
 
Transparent::Transparent(QWidget *parent)
     : QWidget(parent, Qt::FramelessWindowHint)
 {
     setWindowTitle(tr("Transparent Window"));
     setWindowOpacity(0.0);
 }

 
     //window.resize(400, 400);  
     
     //window.setFixedSize(500,500);
     //window.showMaximized();
     
      
 void Transparent::paintEvent(QPaintEvent *)
 {
   QPainter p(this);
   p.setOpacity(1.0);
   p.drawLine(0, 0, 50, 50);        // drawing code
   p.setOpacity(0.0);
 }
   
 QSize Transparent::sizeHint() const
 {
     return QSize(400, 400);
 }

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When i execute the application, the line doesn't appear

[jpn]

setWindowOpacity(0.0);

Just curious, what if you try:

setWindowOpacity(0.01);

setWindowOpacity(0.01);

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I once tried to catch (drag and drop) events with a window having opacity of 0.0. No events were received until I changed the opacity to something non-zero. I think a window with opacity of 0.0 basically means a hidden window and it won't even receive paint events then.

Edit: Oh, and please use "[ code ]"-tags to make code snippets more readable.

[nagpalma]

thanks for your reply jpn, i changed to setWindowOpacity(0.01) but i got the same result

[jpn]

I have my doubts that one could really turn QPainter opaque on a window that has been made transparent at system level. I'm not in Windows right now so I can't test (and neither do I have an extension manager running on X11). But what about testing for example with setWindowOpacity(0.5) if QPainter::setOpacity() really has any effect then?

[nagpalma]

I tried setWindowOpacity(0.5) and i don't think QPainter::setOpacity() has any effect at all

[nagpalma]

Hi,

I confirm, QPainter::setOpacity() had no effect after use setWindowOpacity().
Any suggestions?

Thanks,
nagpalma

[vermarajeev]

Hi,

I confirm, QPainter::setOpacity() had no effect after use setWindowOpacity().
Any suggestions?

Thanks,
nagpalma

This code works for me on windows Xp

Transparent::Transparent(QWidget *parent)
: QWidget(parent) {    
	setWindowTitle(tr("Transparent Window")); 
	setWindowOpacity(0.2f);
}   
void Transparent::paintEvent(QPaintEvent *) {   
	QPainter p(this);  
	p.setPen( QPen( Qt::red ) );
	p.setOpacity(1.0f);   
	p.drawLine(0, 0, 50, 50); 
	p.setOpacity(0.0f); 
} 
int main(int argc, char *argv[]){
	QApplication a(argc, argv);
	Transparent w;
	w.show();
	a.connect(&a, SIGNAL(lastWindowClosed()), &a, SLOT(quit()));
	return a.exec();
}

Transparent::Transparent(QWidget *parent)
: QWidget(parent) {    
	setWindowTitle(tr("Transparent Window")); 
	setWindowOpacity(0.2f);
}   
void Transparent::paintEvent(QPaintEvent *) {   
	QPainter p(this);  
	p.setPen( QPen( Qt::red ) );
	p.setOpacity(1.0f);   
	p.drawLine(0, 0, 50, 50); 
	p.setOpacity(0.0f); 
} 
int main(int argc, char *argv[]){
	QApplication a(argc, argv);
	Transparent w;
	w.show();
	a.connect(&a, SIGNAL(lastWindowClosed()), &a, SLOT(quit()));
	return a.exec();
}

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[jpn]

This code works for me on windows Xp

Make it

p.setPen( QPen( Qt::red, 5 ) );

p.setPen( QPen( Qt::red, 5 ) );

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and you'll notice that the line is transparent too.

[nagpalma]

I tried your code Vermarajeev but like jpn said, the line remains transparent

nagpalma