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

user_245179 0
Viewed 16878

Inside of my QGraphicsRectItem::paint(), I am trying to draw the name of the item within its rect(). However, for each of the different items, they can be of variable width and similarly names can be of variable length.

Currently I am starting with a maximum font size, checking if it fits and decrementing it until I find a font size that fits. So far, I haven't been able to find a quick and easy way to do this. Is there a better, or more efficient way to do this?

Thanks!

void checkFontSize(QPainter *painter, const QString& name) {
 // check the font size - need a better algorithm... this could take awhile
 while (painter->fontMetrics().width(name) > rect().width()) {
  int newsize = painter->font().pointSize() - 1;
  painter->setFont(QFont(painter->font().family(), newsize));
 }
}
font-size autosize qt
8 Answers

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

user_2451790

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).

user_5363680

Follow function based on the answer and comment to the answer allow optimizing font size to fit text in specified rectangle:

QFont optimizeFontSizeToFitTextInRect(QPainter * painter, QRectF drawRect, QString text, int flags = Qt::TextDontClip|Qt::TextWordWrap, double goalError =  0.01, int maxIterationNumber=10){
    painter->save();

    QRect fontBoundRect;
    QFont font;
    double minError = std::numeric_limits<double>::max();
    double error = std::numeric_limits<double>::max();
    int iterationNumber=0;
    while((error > goalError) && (iterationNumber<maxIterationNumber)){
        iterationNumber++;
        fontBoundRect = painter->fontMetrics().boundingRect(drawRect.toRect(),flags, text);
        double xFactor = drawRect.width() / fontBoundRect.width();
        double yFactor = drawRect.height() / fontBoundRect.height();
        double factor;
        if (xFactor<1 && yFactor<1) {
            factor = std::min(xFactor,yFactor);
        } else if (xFactor>1 && yFactor>1) {
            factor = std::max(xFactor,yFactor);
        } else if (xFactor<1 && yFactor>1) {
            factor = xFactor;
        } else {
            factor = yFactor;
        }
        error = abs(factor-1);
        if (factor > 1 ) {
            if (error < minError) {
                minError = error;
            } else {
                break;
            }
        }
        font = painter->font();
        font.setPointSizeF(font.pointSizeF()*factor);
        painter->setFont(font);
    }
    painter->restore();

    return font;
}
user_83820870

Unfortunately, no. There's no easy solution to this. The most obvious improvement, performance-wise would be calculate and cache the needed font size when the text is changed instead of recalculating it in each paintEvent. Another improvement would be to try to estimate the correct size based on the proportions of the bounding rect. Making and testing estimates should get you to correct size much quicker than simply decrementing the point size by one each iteration.

user_47570
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