Changing Opacity in Qlabel

[desch]

Hi Everybody,

I try to change the opacity in QLabel.
Using the paintEvent with this kind of code:

void myLabel::paintEvent(QPaintEvent * e)
{
 
	QPainter p(this);
 
	// if pixmap
	if (! pixmap()->isNull()) 
		p.drawPixmap(pixmap()->rect(), * pixmap());
 
p.setOpacity(0.5); 
 
	// if Text
	if (! text().isEmpty()) 
		p.drawText(rect(), text());
 
}

void myLabel::paintEvent(QPaintEvent * e)
{
	
	QPainter p(this);
		
	// if pixmap
	if (! pixmap()->isNull()) 
		p.drawPixmap(pixmap()->rect(), * pixmap());

p.setOpacity(0.5); 

	// if Text
	if (! text().isEmpty()) 
		p.drawText(rect(), text());
	
}

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The aim is just to change the opacity level ; The problem with this code is that , I have to redraw everything manually : style , pixmap position, text position...
it's not so easy...

If someone has something more easy, it will be fine

Thanks to all

David

[marcel]

You can call the base class paintEvent in your paint event and then just draw all additional stuff.

[desch]

But the problem is :

opacity required :Qpainter

On my label I apply a style sheet, a pixmap, and sometimes a text.

When I do

QPainter p(this);

QPainter p(this);

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eveything must be redraw

and I don't know How to change the opacity with the class QPaintEvent()

Thanks

David

[jpn]

For a transparent pixmap, apply the opacity to the pixmap:

QPixmap original = ...;
 
QPixmap result(original.size());
result.fill(Qt::transparent);
QPainter painter;
painter.setOpacity(0.5);
painter.begin(&result);
painter.drawPixmap(0, 0, original);
painter.end();
 
label->setPixmap(result);

QPixmap original = ...;

QPixmap result(original.size());
result.fill(Qt::transparent);
QPainter painter;
painter.setOpacity(0.5);
painter.begin(&result);
painter.drawPixmap(0, 0, original);
painter.end();

label->setPixmap(result);

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For transparent text, adjust palette:

QPalette palette = label->palette();
QColor color = palette.color(QPalette::Text);
color.setAlpha(127);
palette.setColor(QPalette::Text, color);
label->setPalette(palette);

QPalette palette = label->palette();
QColor color = palette.color(QPalette::Text);
color.setAlpha(127);
palette.setColor(QPalette::Text, color);
label->setPalette(palette);

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or use style sheets:

QLabel { color: rgba(0, 0, 0, 50%) }

QLabel { color: rgba(0, 0, 0, 50%) }

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No reimplementing of paintEvent() needed.

[desch]

I 've tested your exmaple but its didn't work

This is what I've done in a subclass of a label:

void myLabel::setPixmap(const QPixmap & pix)
{
 
		QPixmap result(pix);
		result.fill(Qt::transparent);
 
		QPainter painter;
		painter.setOpacity(0.5);
		painter.begin(&result);
		painter.drawPixmap(0, 0, result);
		painter.end(); 
 
		QLabel::setPixmap(result); 
 
}

void myLabel::setPixmap(const QPixmap & pix)
{

		QPixmap result(pix);
		result.fill(Qt::transparent);
		
		QPainter painter;
		painter.setOpacity(0.5);
		painter.begin(&result);
		painter.drawPixmap(0, 0, result);
		painter.end(); 
		
		QLabel::setPixmap(result); 
	
}

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May I do something wrong ; the pixmap is not visible for me

Thanks

[desch]

after many test : I found my (stupid) problem

the good code on a subclass of QLabel:

QPixmap result(pix.size());
		result.fill(Qt::transparent);
 
		QPainter painter;
		painter.begin(&result);
		painter.setOpacity(0.5);
		painter.drawPixmap(0, 0, pix);
		painter.end(); 
 
		QLabel::setPixmap(result);

QPixmap result(pix.size());
		result.fill(Qt::transparent);
		
		QPainter painter;
		painter.begin(&result);
		painter.setOpacity(0.5);
		painter.drawPixmap(0, 0, pix);
		painter.end(); 
		
		QLabel::setPixmap(result);

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opacity must be done afer the "begin"


Ok thanks to all

David

[jpn]

after many test : I found my (stupid) problem

opacity must be done afer the "begin"

Sorry, that's actually my bad.