QFontDialog::getFont() doesn't use correct font style

pbe · 16 Jul 2016, 09:42

On 2nd glance, maybe it's really better to reply here.
So here comes by better example:

QFontDialog::getFont() doesn't use the correct font style when the font of the font parameter uses toString() and fromString().
It always uses the first font style in the list instead of the style (normal) and weight (regular) of the QFont parameter.
I made an example:

bool ok;

// select a font where `Regular` is not the first item in the `Font
// style` selector (e.g. `Noto Sans`) and select `Regular`
QFont font = QFontDialog::getFont(&ok);
if (ok) {
    // looks like `QFont( "Noto Sans,11,-1,5,50,0,0,0,0,0" )`
    qDebug() << "'font': " << font;

    QFont font2;
    // I originally store the font to the settings and load it again, but
    // that's not even needed to reproduce this problem
    font2.fromString(font.toString());
    // still looks like `QFont( "Noto Sans,11,-1,5,50,0,0,0,0,0" )`
    qDebug() << "'font2': " << font2;

    // now `Bold Italic` is selected, because it's the first item
    QFont font3 = QFontDialog::getFont(&ok, font2, this);

    if (ok) {
        // would now look like `QFont( "Noto Sans,11,-1,5,75,1,0,0,0,0" )`
        qDebug() << "'font3': " << font3;
    }
}

I was testing under:

Platform: linux
Operating System: KDE neon User Edition 5.7
Build architecture: x86_64
Current architecture: x86_64
Qt Version (build): 5.7.0
Qt Version (runtime): 5.7.0

(The problem was initially reported by a user of QOwnNotes at https://github.com/pbek/QOwnNotes/issues/239.)

Am I doing something wrong?
Thanks a lot for your help!

kshegunov · P pbe 16 Jul 2016, 09:02

@pbe said:

On 2nd glance, maybe it's really better to reply here.

It is, indeed, for several reasons.

The whole problem history is at a glance
The people who responded will get a notification there's activity on the topic.
The additional information may attract more or better answers

and so on.

Kind regards.

kshegunov · P pbe 16 Jul 2016, 09:02

@pbe
Hi,
There's a bug - QTBUG-52741 that appears to be what you're describing. I also run your example through the debugger after I was able to reproduce (Qt 5.7) and the problem is indeed in the dialog, here.

The dialog matches the family only, and when it calls setCurrentItem it selects the very first item in the model (which has the default style), which in turn will overwrite the member that holds the style and you get what you described. If you use the font object directly you won't get the bug, i.e.:

QFont font = QFontDialog::getFont(&ok);
if (ok)  {
    // ...
    QFont font2 = QFontDialog::getFont(&ok, font, this); //< Works correctly, no bug
    // ...
}

Kind regards.

pbe · 19 Jul 2016, 18:22

@kshegunov, I already found that bug and was wondering if that's what's affecting QOwnNotes. Thank you for making that clear!

Yes, you are right. If you use the font directly it works, but it doesn't work with font2.fromString(font.toString()); that is needed to store and load it to/from the settings. Do you have any ideas to get around this?

kshegunov · P pbe 18 Jul 2016, 05:12

@pbe said:

Do you have any ideas to get around this?

Sadly, no. The bug seems inherent to the QFontDialog class when the QFont's internal identifier isn't set (i.e. when the dialog needs to go and query about the font by its attributes). If I get some more time in the coming days, I'll try to run it again and hopefully will have something better.

Kind regards.

pbe · 24 Jul 2016, 13:57

@kshegunov, thank you very much! You are my hero!

kshegunov · 24 Jul 2016, 16:40

@pbe
I have a bug fix and I'll try to submit it this evening (I've been working in the dev branch, so some git magic is needed).

Kind regards.

pbe · 24 Jul 2016, 18:45

@kshegunov, really? That's wonderful! I can't wait to see it!

kshegunov · P pbe 24 Jul 2016, 16:40

@pbe
https://codereview.qt-project.org/#/c/165958/

We'll see if it gets approved.

pbe · 25 Jul 2016, 12:30

Thanks a lot, I will watch that request!

kshegunov · P pbe 24 Jul 2016, 19:48

@pbe
There's something else, while investigating your bug I stumbled upon this one ... which you may actually encounter, although it's somewhat unrelated to your problem with the dialog.

pbe · wrote on 25 Jul 2016, 13:06

@kshegunov, that really is what I'm encountering... So actually two bugs are triggered here...

pbe · 3 Aug 2016, 15:28

Really thanks a lot for your help!

kshegunov · P pbe 25 Jul 2016, 13:09

@pbe
QTBUG-54936's been merged and the patch will be incorporated in Qt 5.8

Kind regards.

pbe · 3 Aug 2016, 22:04

@kshegunov, great news! Thanks a lot!

kshegunov · 4 Aug 2016, 04:40

@pbe
My pleasure. The dialog bug is low(er) priority and it may take some time for the proposed patch to get reviewed.

Kind regards.

pbe · 4 Aug 2016, 11:09

@kshegunov I wonder if it will get fixed at all...

kshegunov · 4 Aug 2016, 12:14

@pbe
It's going to, it'ill just take some time. Now things a bit slow because most people are on vacation.

pbe · wrote on 4 Aug 2016, 12:14

@kshegunov, humans... :)