QFont pixelSize和QFontMetrics高度给出不同的值

Question

I am creating a custom label and want it to have a 13 pixel high text and setting label's max height to 14.

textFont.setFamily("Frutiger LT Com 55 Roman");
textFont.setPixelSize(13);
setFont(textFont);
QFontMetrics fm(this->font());
QFontInfo fi(this->font());
qDebug()<<"QFontMetrics"<<fm.height()<<fm.xHeight()<<fm.ascent()<<fm.descent();
qDebug()<<"QFontInfo"<<fi.exactMatch()<<fi.family()<<fi.pixelSize();

This is what I get

QFontMetrics 16 3 13 3 
QFontInfo true "Frutiger LT Com 55 Roman" 13

Why am I getting height as "16" when I am setting pixelSize as "13"? And because of this text on my label is getting clipped from bottom (Vertically center aligned).

QFontMetrics "height()" definition says height=ascent+descent+1(for baseline). But as you can see above ascent=13, descent=3 and height=16. This contradicts "height()" function definition.

Answer 1

This seems to be bug in documentation of Qt 5 (someone just forgot to change some Doxygen comments).

Commit that removes the +1 is here: https://qt.gitorious.org/qt/qtbase/commit/cb8445f0323b0eefbb04f1d8adad81a00b53abd8

The commit says:

Remove historical +1 from font height calculation

Historically, we've calculated font height as ascent+descent+1. In Qt 4, a patch was added to work around this by subtracting 1 from the descent of the font engines. We now remove the +1 and the work arounds.