For Qt 4.6.x, how to auto-size text to fit in a specified width?

Johannes from qtcentre.org offered the following solution:

float factor = rect().width() / painter->fontMetrics().width(name);
 if ((factor < 1) || (factor > 1.25))
 {
  QFont f = painter->font();
  f.setPointSizeF(f.pointSizeF()*factor);
  painter->setFont(f);
 }

I gave it a try in my program and so far, it seems to work quite well. I like it because it produces results in one pass, but it assumes that font width scales like its height.

http://www.qtcentre.org/threads/27839-For-Qt-4-6-x-how-to-auto-size-text-to-fit-in-a-specified-width

void myClass::adaptFontSize(QPainter * painter, int flags, QRectF drawRect, QString text){
     int flags = Qt::TextDontClip|Qt::TextWordWrap; //more flags if needed
     QRect fontBoundRect = 
           painter->fontMetrics().boundingRect(drawRect.toRect(),flags, text);
     float xFactor = drawRect.width() / fontBoundRect.width();
     float yFactor = drawRect.height() / fontBoundRect.height();
     float factor = xFactor < yFactor ? xFactor : yFactor;
     QFont f = painter->font();
     f.setPointSizeF(f.pointSizeF()*factor);
     painter->setFont(f);

 }

or more accurate but greedy

 void myClass::adaptFontSize(QPainter * painter, int flags, QRectF rect, QString text, QFont font){
     QRect fontBoundRect;
     fontBoundRect = painter->fontMetrics().boundingRect(rect.toRect(),flags, text);
     while(rect.width() < fontBoundRect.width() ||  rect.height() < fontBoundRect.height()){
         font.setPointSizeF(font.pointSizeF()*0.95);
         painter->setFont(font);
         fontBoundRect = painter->fontMetrics().boundingRect(rect.toRect(),flags, text);
     }
 }

Here is my code the fit (in heigth) a text, works quite well (error < 2% I guess)

void scalePainterFontSizeToFit(QPainter &painter, QFont &r_font, float _heightToFitIn)
{
    float oldFontSize, newFontSize, oldHeight;

    // Init
    oldFontSize=r_font.pointSizeF();

    // Loop
    for (int i=0 ; i<3 ; i++)
    {
        oldHeight = painter.fontMetrics().boundingRect('D').height();
        newFontSize = (_heightToFitIn / oldHeight) * oldFontSize;
        r_font.setPointSizeF(newFontSize);
        painter.setFont(r_font);
        oldFontSize = newFontSize;
        //qDebug() << "OldFontSize=" << oldFontSize << "HtoFitIn=" << _heightToFitIn << "  fontHeight=" << oldHeight << "  newFontSize=" << newFontSize;
    }

    // End
    r_font.setPointSizeF(newFontSize);
    painter.setFont(r_font);
}

You could have a QGraphicsTextItem as a child of the rect item, measure the text item's width and then scale the text item (setTransform()) to fit into the rect item's width (and height).