[Interest] Text rendering problem.

[Elvis Stansvik]

2015-07-18 1:13 GMT+02:00 Bill Crocker <william.crocker at analog.com>:
>
> Hello:
>
> I am having a text rendering problem.
>
> The following code creates a QLabel and QGraphicsTextItem.
> The QLabel text is 60 pt. The QGraphicsTextItem text size is 6 pt,
> but then the view is scaled up by 10x. So, in the end both
> pieces of text are the same size on the screen.
>
> For me the QLabel text looks good while the
> QGraphicsTextItem is very badly kerned (char spacing).
>
> Does anyone know what is wrong
> with the QGraphicsTextItem implementation?

>From some googling, I think it's because the hinting values are
obtained when unscaled, and then used even when scaled.

What you can do in your example is

   scene_font.setHintingPreference(QFont::PreferNoHinting);

to prefer that hinting not be used at all. I tested this on X11/Linux.
I'm attaching the before/after results.

I'm not sure what effect this setting has on all the platforms, but
it's just a hint so I guess it might be ignored on some of them.

Cheers,
Elvis

>
>
> (For all I know the QLabel text would be badly kerned
>   at 6pt as well, but it is hard to see.)
>
> Qt 4.8.6, RHEL 5.10
>
> Thanks.
>
> Bill
>
> -------------------------
> int
> main( int argc, char **argv ) {
>      QApplication app(argc,argv);
>
>      int sz = 6, scale = 10;
>      QString text = QString("Impedance");
>
>      // Text size is 60.
>      // This text renders well.
>      QFont label_font = QFont("Arial",scale*sz,QFont::Bold);
>      QLabel *label = new QLabel(text);
>      label->setFont(label_font);
>
>      // Text size is 6, then the view is zoomed in x10.
>      // This text is not properly kerned.
>      QFont scene_font = QFont("Arial",sz,QFont::Bold);
>      QTextDocument *html = new QTextDocument;
>      html->setDefaultFont(scene_font);
>      html->setHtml(text);
>      QGraphicsTextItem *gi = new QGraphicsTextItem;
>      gi->setDocument(html);
>      QGraphicsScene *sp = new QGraphicsScene;
>      sp->addItem(gi);
>      QGraphicsView *view = new QGraphicsView;
>      view->setScene(sp);
>      view->scale(scale,scale);
>
>      QHBoxLayout *hbox = new QHBoxLayout;
>      hbox->addWidget(label);
>      hbox->addWidget(view);
>
>      QWidget *wp = new QWidget;
>      wp->setLayout(hbox);
>      wp->show();
>
>      app.exec();
> }
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