[Qt-interest] QFont/QFontMetrics oddity

[Girish Ramakrishnan]

Hi Chris,
In general, unless otherwise it's a container class (like QList,
QVector) always create Qt objects _after_ QApplication is created. From
the docs "Note that a QApplication instance must exist before a QFont
can be used." (http://qt.nokia.com/doc/4.6/qfont.html). In your case,
gFont gets created before QApplication is created and I suspect that is
the problem.

Girish

Chris wrote:
> I ran into a painting problem in my application that I was able to
> reproduce with the following code:
> 
> #include <QFontMetrics>
> #include <QtDebug>
> #include <QApplication>
> #include <QPaintEvent>
> #include <QWidget>
> #include <QPainter>
> 
> const QFont gFont( "Arial", 9 );
> 
> class Widget : public QWidget
> {
>     protected:
> 
>         void paintEvent( QPaintEvent * )
>         {
>             QPainter painter( this
> );                                                                                                                                                                                                    
> 
> 
>             QFont font( "Arial", 9 ); //only used for comparison purposes
> 
>             painter.setFont( gFont );
>             QFont pFont = painter.font();
> 
>             QFontMetrics m1( gFont );
>             QFontMetrics m2( pFont );
>             QFontMetrics m3( font  );
> 
>             qDebug() << "The same?" << ( pFont == font );
>             qDebug() << "m1 width:" << m1.width( "100" );
>             qDebug() << "m2 width:" << m2.width( "100" );
>             qDebug() << "m3 width:" << m3.width( "100" );
>         }
> };
> 
> int main( int argc, char *argv[] )
> {
>     QApplication app( argc, argv );
> 
>     Widget w;
>     w.show();
> 
>     return app.exec();
> }
> 
> On my Windows box I get the following output:
> The same? true
> m1 width: 15
> m2 width: 21
> m3 width: 21
> 
> Can anyone explain why the calculated with of the width of the font
> instantiated in the global scope would be different than the others?