QLineEdit - wrong placeholderText's color on Linux Mint dark theme

Kobid

Hi,
I have Linux Mint 22.1 Cinnamon with dark theme Mint-Y.
When creating UI, in design I see correct gray color for placeholderText:

But when I run app:

Why it is like that? It is default Qt Widgets App so I guess it is using Fusion Style. Everything else is perfect, just like GTK, green accent colors etc. Note that I have some Qt apps already installed for example Keepassx which is Qt and placeholders also have correct gray color. All other native GTK apps also have gray placeholders.
I had this issue on Qt 6.8 and now updated to 6.9 it is still

SGaist

Hi,

Which version of Qt is provided by your distribution ?
Did you try to build your application with it ?

cristian-adam

You can give PhantomStyle a try.

Phantom is a QStyle for Qt which began as an overhaul of QFusionStyle. Similar to Fusion, it's designed to be a looks-the-same cross-platform style. It looks native to nobody, but familiar to many. It has the visual appearance of a traditional GUI, and does not adopt a "modern flat" style. Compared to Fusion, it has many fixes, objective improvements, and subjective improvements.

I have packaged a Qt Creator plugin https://github.com/cristianadam/qt-creator-phantomstyle which uses PhantomStyle. So that you can see it in action.

If you want to use it in your application you can add these lines to your CMakeLists.txt:

include(FetchContent)
FetchContent_Declare(PhantomStyle
  GIT_REPOSITORY "https://github.com/cristianadam/phantomstyle.git")
FetchContent_MakeAvailable(PhantomStyle)

target_link_libraries(<CoolApp> PRIVATE PhantomStyle)

and in your main.cpp:

// ...
#include <phantom/phantomstyle.h>

int main() {
   // ...
   QApplication::setStyle(new PhantomStyle);
   // ...
}

KeePassXC is using a variation of PhantomStyle.

By having your own style, you can modify it to your eyes desire 😊

Kobid

@SGaist said in QLineEdit - wrong placeholderText's color on Linux Mint dark theme:

Hi,

Which version of Qt is provided by your distribution ?
Did you try to build your application with it ?

Seems that installing Keepassx (I think it is the only Qt app which I installed from Mint repo, other ones are from flatpak) I got 5.15.13 as dependency packages:

qmake --version
QMake version 3.1
Using Qt version 5.15.13 in /usr/lib/x86_64-linux-gnu

Command dpkg -l | grep qt also return similar packages:

I didn't try to compile on these versions yet

@cristian-adam Can you provide .pro example? C++ is my secondary language and I'm polishing it on Qt where I mostly use qmake and .pro. Even if Phanton fix the problem, it is sad that so silly placeholderText has this problem in default Qt Style

Kobid

Ok I have installed PhantonStyle and it also has black placeholder (on the right):

Here is for example my app written in wxWidgets with GTK and placeholder is correct:

cristian-adam

I think it has something to do with the default palette, which can vary from operating system to operating system.

If I look at https://doc.qt.io/qt-6/qpalette.html it could be that for some entry, like QPalette::PlaceholderText the light theme color value is being used instead of the dark theme one.

cristian-adam

You can change the QPalette::PlaceholderText to something else, see:

int main(int argc, char *argv[])
{        
    QApplication a(argc, argv);

    QPalette pal = QApplication::palette();
    pal.setColor(QPalette::PlaceholderText, pal.color(QPalette::Mid));
    QApplication::setPalette(pal);

Kobid

Thank you @cristian-adam . Found something interesting. The QPalette::Mid was too much alike to edit background so I played with different types to get something close to GTK placeholder color. Finally did something stupid just for curiosity:

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    //QApplication::setStyle(new PhantomStyle);

    QPalette pal = QApplication::palette();
    pal.setColor(QPalette::PlaceholderText, pal.color(QPalette::PlaceholderText));
    QApplication::setPalette(pal);

    MainWindow w;
    w.show();
    return a.exec();
}

And the result is:

What happened there? Palette don't have initialized color for QPalette::PlaceholderText color role?

cristian-adam

It looks like a bug. Please do open up a bug report at https://bugreports.qt.io

Hopefully the Qt Widgets maintainers have more ideas why this is happening. But now you have a workaround.

Does:

   QPalette pal = QApplication::palette();
    QApplication::setPalette(pal);

work? Or you have to explicitly set QPalette::PlaceholderText ?

Kobid

No. That doesn't work.
Ok I'll submit a bug report.
Thank you

Christian Ehrlicher

You should check it with a recent Qt version first before creating a bug report

Kobid

Yo mean preview version? Because I have recent stable 6.9

Christian Ehrlicher

In your images above you use Qt5

Kobid

The installed one in linux mint (Keepassx installed this version) is 5.15. For my project I'm using 6.9 in custom installation

Christian Ehrlicher

Ok, then all is fine, create a bug report. Looks like a problem with the gtk platform plugin.
Maybe it's also related to https://bugreports.qt.io/browse/QTBUG-86195

Kobid

Created ticket if someone come here with similar problem:
https://bugreports.qt.io/browse/QTBUG-136075

Kobid

@Christian-Ehrlicher said in QLineEdit - wrong placeholderText's color on Linux Mint dark theme:

Ok, then all is fine, create a bug report. Looks like a problem with the gtk platform plugin.
Maybe it's also related to https://bugreports.qt.io/browse/QTBUG-86195

Weird, I searched first for placeholdertext keyword and didn't find anything. Anyway, that one is for Windows 10 reported in 2023

Christian Ehrlicher

@Kobid said in QLineEdit - wrong placeholderText's color on Linux Mint dark theme:

Anyway, that one is for Windows 10 reported in 2023

Please read the full bug report. It's also for linux.

Kobid

You are right