Maintaining Consistent Font Appearance in PySide6 QLabel: QSS vs. QFont

[Emrecp]

Hello,
When I change the font property of a QLabel using QSS in PySide6, it appears as intended. However, when I try to do the same using QFont directly, it appears differently. I want the appearance to be consistent with the one achieved using QSS even when I use QFont. Is there a way to achieve this, or is it a problem?

Seeking to Achieve the Same Look as the First Label
PySide6: 6.4.2
Python: 3.11.2 x64

Code:

from PySide6.QtWidgets import *
from PySide6.QtGui import *
import sys

if __name__ == '__main__':
    app = QApplication(sys.argv)
    wid = QWidget(); lay = QVBoxLayout(wid)
    label = QLabel("HELLO! MY NAME IS EMRE")
    label.setStyleSheet("""font:'SF Pro Display';
    font-size:14pt;
    font-weight:900;""")


    label2 = QLabel("HELLO! MY NAME IS EMRE")
    font = QFont('SF Pro Display', 14)
    font.setWeight(QFont.Weight.Black) # 900
    label2.setFont(font)


    lay.addWidget(label)
    lay.addWidget(label2)
    wid.show()
    sys.exit(app.exec())

[JonB]

@Emrecp
I believe @SGaist is telling you that you cannot guarantee that a widget with a stylesheet will look identical to one you construct with coded style attributes. As soon as you place a stylesheet on a widget you are (potentially) losing some styles which are inbuilt, so it may differ.

I suggested earlier you remove the weight stuff in your example and see whether just with the font in "normal" it does or does not look identical using the same font in both code and stylesheet.

If you are coding inside paintEvent() then, as you say, you cannot use stylesheet. You can only set the attributes on a QFont as you have done.

I don't know whether you can go through the sources of Qt to discover just what a current style like Fusion does.

[JonB]

@Emrecp
I don't know. But I would start by removing the font weight on each one. Are they then identical or different? And while you're there I presume it does not matter which font (name) you use (e.g. Arial)?

[SGaist]

Hi,

Setting a stylesheet nukes the current style used to render the widget it's applied on hence you might see differences.

[JonB]

@SGaist
Either I misunderstand the OP or I misunderstand you or I misunderstand the code. He is comparing one example 100% stylesheet against another example 100% code, no? And wants/expects them to be identical.

[SGaist]

@JonB you understood correctly. But as I wrote, two different styles are used, hence there can be difference.

I would also check the fonts effectively used by the widgets to compare their values.

[JonB]

@SGaist said in Maintaining Consistent Font Appearance in PySide6 QLabel: QSS vs. QFont:

But as I wrote, two different styles are used, hence there can be difference.

I still don't understand. Maybe the OP will.

ISTM he is asking whether

    label.setStyleSheet("""font:'SF Pro Display';
    font-size:14pt;
    font-weight:900;""")

should be equated identically via

    font = QFont('SF Pro Display', 14)
    font.setWeight(QFont.Weight.Black) # 900
    label2.setFont(font)

Setting a stylesheet nukes the current style used to render the widget

Yes. But what current style was used for the QLabel in the above code? I don't see any? So I don't see setting the stylesheet has any style to nuke here?

[SGaist]

@JonB each platform has a default style to render the application. Setting a stylesheet triggers the replacement of the current style by the one that handles the stylesheet hence the "strange" look you get when changing elements such as buttons or QTabBar. It's more visible on platforms such as macOS or Windows.

[JonB]

@SGaist said in Maintaining Consistent Font Appearance in PySide6 QLabel: QSS vs. QFont:

each platform has a default style to render the application.

Ohhhh. Is this what I have seen about Fusion style and never understood? So that's some base CSS files for QLabels etc. to start with? I didn't know that, do you have the doc link which explains? Should be of interest to the OP.

[SGaist]

@JonB there's no CSS involved in the platform styles.

You can check the styles example.

KDAB has a very good article about dumping stylesheets in favor of custom styles.

[Emrecp]

@SGaist I want to use this font in a paintEvent in my own project. Since I can't use stylesheet in paintEvent, I need how to get the same text with qfont. Just tell me the solution please

[JonB]

@Emrecp
I believe @SGaist is telling you that you cannot guarantee that a widget with a stylesheet will look identical to one you construct with coded style attributes. As soon as you place a stylesheet on a widget you are (potentially) losing some styles which are inbuilt, so it may differ.

I suggested earlier you remove the weight stuff in your example and see whether just with the font in "normal" it does or does not look identical using the same font in both code and stylesheet.

If you are coding inside paintEvent() then, as you say, you cannot use stylesheet. You can only set the attributes on a QFont as you have done.

I don't know whether you can go through the sources of Qt to discover just what a current style like Fusion does.