QFontDatabase/QFont question

[Charles]

variableAxisTags displays the tags that you have set, not the available
tags for the font.

I think whether a font is variable or not should be transparent to the user
because it is an implementation detail.

If you really want to check it you can just see if setting the tags change
anything

def is_variable(font):
    f = QFont(font)
    f.setVariableAxis(QFont.Tag('wght'), 800)
    return 'ExtraBold' in QFontInfo(f).styleName()


print(is_variable('Exo')) # True
print(is_variable('Arial')) # False

On Sun, Jan 12, 2025 at 1:37 AM John Sturtz <john at sturtz.org> wrote:

> I did actually delve into that a little bit.  It seemed to be
> unrewarding.  My experience was as follows:
>
> For all the fonts (that I looked) on my system, .variableAxisTags()
> initially returns an empty list when a font object is created, both for
> fonts that the Win font dialog reports as variable and ones that it doesn't
> report as variable.  For example, in both these cases:
>
>     f = QFontDatabase.font('Arial', 'Regular', 24)
>     print(f.variableAxisTags())
>
>     f = QFontDatabase.font('Exo', 'Thin', 24)
>     print(f.variableAxisTags())
>
> the print() displays an empty list.  Arial isn't variable, so I wouldn't
> expect anything there.  But Exo is, and the value for the 'wght' axis for
> the font created should be 100 ('Thin').  But that doesn't affect the list
> that .variableAxisTags() returns.  So Qt doesn't seem to fill that list;
> only user code apparently.
>
> Setting the 'wght' variable axis with .setVariableAxis() does indeed seem
> to work for Exo.  This:
>
>     f = QFontDatabase.font('Exo', 'Regular', 24)
>     f.setVariableAxis(QtGui.QFont.Tag('wght'), 800)
>     print(f.variableAxisTags())
>
> does display Exo ExtraBold.  And the print() statement now shows a Tag
> object in the list.  (Oddly, though setting the 'wght' axis in this
> manner worked as I expected, I couldn't get setting the 'ital' axis to
> cause italic to be displayed ...)
>
> Setting these axes for a font that is (according to Win settings) not
> variable also adds an item to the variable axis tags list.  This code runs:
>
>     f = QFontDatabase.font('Arial', 'Regular', 24)
>     f.setVariableAxis(QtGui.QFont.Tag('wght'), 800)
>     print(f.variableAxisTags())
>
> Here also, the print() statement displays a Tag item in the list.  It
> doesn't generate any sort of error, and by all appearances seems to
> 'succeed'.  Of course, it doesn't change the font that's displayed, because
> Arial isn't variable.
>
> As far as I could tell, the only thing in the picture that would clue me
> in that Exo is variable and Arial is not is that the .setVariableAxis()
> call didn't change the appearance of the displayed font.  But nothing
> programmatically.  It would be lovely if QFontDatabase or QFont had
> something like .isVariable(), or some such.  But evidently not ...
>
> /John
>
> ------ Original Message ------
> From "Maurizio Berti" <maurizio.berti at gmail.com>
> To "John Sturtz" <john at sturtz.org>
> Cc "Charles" <peacech at gmail.com>; pyqt at riverbankcomputing.com
> Date 1/11/2025 9:33:18 AM
> Subject Re: Re[6]: QFontDatabase/QFont question
>
> I've not used variable fonts yet, but you should probably start by
> inspecting the QFont instance using the related "variable" and "tag"
> functions introduced in 6.7, such as
> https://doc.qt.io/qt-6/qfont.html#variableAxisTags
> Maybe you can create a small program that lists all fonts and the results
> of those functions, then compare it with the Windows font dialog.
>
> Cheers,
> MaurizioB
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://www.riverbankcomputing.com/pipermail/pyqt/attachments/20250112/18b68118/attachment-0001.htm>