transparent background

I've a problem....I create myWidget (with a it's own paint Event) and now I want that its background is transparent so that it's background is the same of the portion of its parent widget displayed covered by myWidget. Any Idea?

You can set a mask(but you will get rough edges) or you can first fill the widget with a transparent color or transparent pixmap and then paint on it.

But this will only work as long as the widget''s position is restricted to its parent bounds(won't work for floating widgets).

Quote:

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Originally Posted by marcel

You can set a mask(but you will get rough edges) or you can first fill the widget with a transparent color or transparent pixmap and then paint on it.

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ok... an example of transparent color an one for transparent pixmap?

Quote:

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Originally Posted by marcel

But this will only work as long as the widget''s position is restricted to its parent bounds(won't work for floating widgets).

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perfect, this is what I want. ;)

Quote:

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Originally Posted by fruzzo

ok... an example of transparent color an one for transparent pixmap?

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Set the Brush to a QColor with an appropriate alpha value.
http://doc.trolltech.com/main-snapsh....html#setAlpha
http://doc.trolltech.com/main-snapsh...lended-drawing

Quote:

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Originally Posted by momesana

Set the Brush to a QColor with an appropriate alpha value.
http://doc.trolltech.com/main-snapsh....html#setAlpha
http://doc.trolltech.com/main-snapsh...lended-drawing

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We're talking about Qt3 here...

Quote:

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Originally Posted by wysota

We're talking about Qt3 here...

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Oops.
There is an artikel about transparency in QT-4.1 but it also discusses the ways transparency can be achieved with Qt3 without going too much into details. It's a good read.
http://www.google.de/url?sa=t&ct=res...q35D9U1yFV_Daw

I've solved the problem in this way....but using QBitmap I can draw only with white color, any idea how to modify the code to draw in other colors?

Code:

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#include "azimutscale.h"
#include <qpainter.h>
#include <qbitmap.h>
 
AzimutScale::AzimutScale( QWidget *parent, const char *name)
    : mapParent(parent), QWidget( parent, name )
{
     resize(parent->width()*0.9, parent->height()*0.9);
}
 
 
void AzimutScale::paintEvent( QPaintEvent * )
{
 
    QBitmap bm( size() );
    bm.fill( color0 );			//transparent
    QPainter paint;
    paint.begin( &bm, this, false );
    drawScale( &paint );
    paint.end();
    setMask( bm );
 
}
 
void AzimutScale::drawScale( QPainter *paint )
{
   /*QColor mainTagsColor (127,0,127);
   QColor tagsColor( 127,127,191);*/
 
   QColor mainTagsColor (color1);
   QColor tagsColor( color1);
 
    paint->setWindow( -500,-500, 1000,1000 );
 
    QRect v = paint->viewport();
    int d = QMIN( v.width(), v.height() );
    paint->setViewport( v.left() + (v.width()-d)/2,
			v.top() + (v.height()-d)/2, d, d );
 
 
    //Draw cross at center of scale
    paint->setPen(QPen(mainTagsColor,1));
    paint->drawLine( 0, -50, 0, 50 );
    paint->drawLine( -50, 0, 50,0 );
 
   //Draw main scale
   QFont fontLabel ("times", 15, QFont::Bold);
   QFontMetrics fm (fontLabel);
 
    for ( int i=0; i<12; i++ ) {
	//draw label
	paint->setPen(mainTagsColor);
	paint->setFont(fontLabel);
	QString label = QString::number(i*30);
	int pixWidth = fm.width(label);
	paint->drawText(0-pixWidth/2, -480, label);
	//draw tag
	paint->setPen(QPen(mainTagsColor,1));
	paint->drawLine( 0, -300, 0, -470 );
	paint->rotate( 30 );
    }
 
    //Draw minus scale
    paint->setPen(tagsColor);
    for ( int j=0; j<60; j++ ) {
	if ((j%5) !=0 )
		paint->drawLine( 0, -450, 0, -470 );
	paint->rotate( 6 );
    }
}

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Use its superclass - QPixmap.

Quote:

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Originally Posted by wysota

Use its superclass - QPixmap.

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mhmm I've just try to use it to but I don't undestand how to do the same thing! :confused:

Just looked at your code again. Try this:

Code:

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void xxx::paintEvent(...){
  QPainter p(this);
  drawScale(&p);
  // then set the mask as you did earlier
  //...
}

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I try this but It seems don't work.

Code:

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void AzimutScale::paintEvent( QPaintEvent * ){   
QPainter paint;      
drawScale( &paint ); 
QBitmap bm( size() );   
 bm.fill( color0 );
setMask( bm );    
}

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Define "doesn't work". The mask is certainly invalid...

Quote:

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Originally Posted by wysota

Define "doesn't work". The mask is certainly invalid...

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"doesn't work" = the widget is filled with black color and don't draw anithing.

I suggest you take a look at some working paintEvent() implementation, because yours doesn't make any sense. Look how you created the painter object - you didn't tell it what to paint on.