Certain special characters are not shown on Windows

[davidebeatrici]

Reported by @Natenom.

Example string: ᎭᎪᎢᎬᎭᎾᎷ

All characters are shown as empty space.

[Krzmbrzl]

It seems that it can happen that the used font does not contain the used characters. See https://forum.qt.io/topic/82243/some-unicode-characters-not-displayed-on-ui/3

There it is suggested that this can be checked with the following snippet:

QFont f("DejaVu sans");
QFontMetrics fm(f);
qDebug() << fm.inFont(QChar(2399)) << fm.inFont(QChar(2386));

I guess we'd instead want to use the font from our main application instead of providing the font name explicitly... (And obviously we'll have to use different character codes)

@davidebeatrici you said you can reproduce - could you try to verify that these characters are contained in the used font?

[davidebeatrici]

QFontMetrics fm(qApp->font());
qDebug() << fm.inFont(QChar(0x13AD)) << fm.inFont(QChar(0x13AA)) << fm.inFont(QChar(0x13A2))
		 << fm.inFont(QChar(0x13AC)) << fm.inFont(QChar(0x13AD)) << fm.inFont(QChar(0x13BE))
		 << fm.inFont(QChar(0x13B7));

true true true true true true true

[Krzmbrzl]

Hm okay.

Btw.: Why did you label this issue as upstream-bug? Do you already have evidence that this is not our fault? And if so: Why is this ticket still open? 🤔

[davidebeatrici]

I'm pretty sure it's an upstream bug because Windows has no issues showing those characters.

The ticket is still open because we have to either find a workaround or fix the issue in Qt.

[Krzmbrzl]

I guess in order to verify that this is an upstream Bug, we'd have to create a minimal example that also fails to display this String.
I think a simple label with this text should be sufficient. Plus it should probably include the check for whether these characters are contained in the used font. And if we have verified this in this way, we can file a report against Qt and close this issue here as an upstream issue.

Should that minimal example be capable of displaying this String, then the issue is probably on our side somewhere 🤔

[davidebeatrici]

Done: https://github.com/mumble-voip/qt_unicode_test

String: "ᎭᎪᎢᎬᎭᎾᎷ"
Character '\u13ad' in font: true
Character '\u13aa' in font: true
Character '\u13a2' in font: true
Character '\u13ac' in font: true
Character '\u13ad' in font: true
Character '\u13be' in font: true
Character '\u13b7' in font: true

[Krzmbrzl]

Upstream report: https://bugreports.qt.io/browse/QTBUG-93183

Until proven otherwise I'll close this as an upstream bug

[Kissaki]

@Krzmbrzl Shouldn’t this be listed as a known issue in our release notes then? Or is this specific to master rather than our stable too?

[Krzmbrzl]

It seems to only be an issue with 1.4.0 snapshots.
But I guess for them we should probably add it...

[davidebeatrici]

No, it's an issue in 1.3.x too.

I didn't try to reproduce in 1.2.x.

[Krzmbrzl]

No, it's an issue in 1.3.x too.

@davidebeatrici Did you verify that? 'cause if I remember correctly @Natenom mentioned that this was only observed since 1.4.0 snapshots 🤔