How to detect missing font characters

Question

Is there a way to detect that all characters are displayed properly with the current font? In some environments and fonts certain characters are replaced with a square symbol.

I'd like to automatically verify that all characters used in the GUI are supported by the current font.

Answer 1

I found a possible solution using the QFontMetrics class. Here is a an example function to query whether all characters are available in the current text of a QLabel:

bool charactersMissing(const QLabel& label) {
    QFontMetrics metrics(label.font());
    for (int i = 0; i < label.text().size(); ++i) {
        if (!metrics.inFont(label.text().at(i))) {
            return true;
        }
    }
    return false;
}

Of course displaying to the user which character is missing would be good, but of course that has to be done with a different font :)

Answer 2

According to this discussion, I don't think the sample code of QFontMetrics will work well. https://bugreports.qt-project.org/browse/QTBUG-1732

The QFontMetrics inFont() function depend on QFont class, and it seems you have to set the StyleStrategy to QFont::NoFontMerging. But actually, the NoFontMerging flag doesn't work in that way you think, so the inFont function still return true if other fonts in your system have this glyph.

BTW, I make a verification tool in python finally.

https://github.com/diro/pyGlyphChecker