Making Qt Application that work with different System Font Sizes

Question

I am working on a Qt application targeting Windows and Mac OS X. I have lots of dialogs with text in my application. I created the application on Windows, where I sized the dialogs to fit all of my text neatly. As soon as I compiled on Mac OS X, I realised all of the text doesn't fit properly. Furthermore, setting a different system font size in the Windows Control Panel causes all of dialog sizes to be incorrect.

How are you supposed to handle different system font sizes in Qt?

It is complex problem. During customization you should not use any "fixed" values. For example, all fonts sizes should be set in relative values (not in pixels). — Dmitry Sazonov, Jul 22 '13 at 08:42
Check out this related thread: http://stackoverflow.com/questions/20464814/changing-dpi-scaling-size-of-display-make-qt-applications-font-size-get-rendere/29417620#29417620 — BuvinJ, Apr 02 '15 at 16:19

Frodon · Accepted Answer · 2013-07-22T15:04:37.057

You don't: you let Qt do the job for you. Use layouts to arrange your widgets; avoid setting fixed sizes. Last point: I recommend to use Qt-Designer to create your interfaces.

Edit for Dmitry: here are Python files from 2 ui files (generated with pyuic4) each one with 2 QLabel. 1 Qlabel font is huge (72), the other is the default one (10).

Min and Max size are constrained: here if max font size is 10, the label is correctly displayed.

from PyQt4 import QtCore, QtGui

class Ui_Dialog(object):
    def setupUi(self, Dialog):
        Dialog.setObjectName("Dialog")
        Dialog.resize(115, 160)
        sizePolicy = QtGui.QSizePolicy(QtGui.QSizePolicy.Fixed, QtGui.QSizePolicy.Fixed)
        sizePolicy.setHorizontalStretch(0)
        sizePolicy.setVerticalStretch(0)
        sizePolicy.setHeightForWidth(Dialog.sizePolicy().hasHeightForWidth())
        Dialog.setSizePolicy(sizePolicy)
        Dialog.setMinimumSize(QtCore.QSize(115, 160))
        Dialog.setMaximumSize(QtCore.QSize(115, 160))
        self.verticalLayout = QtGui.QVBoxLayout(Dialog)
        self.verticalLayout.setObjectName("verticalLayout")
        self.label = QtGui.QLabel(Dialog)
        font = QtGui.QFont()
        font.setFamily("Andale Mono")
        font.setPointSize(72)
        self.label.setFont(font)
        self.label.setObjectName("label")
        self.verticalLayout.addWidget(self.label)
        self.label_2 = QtGui.QLabel(Dialog)
        self.label_2.setObjectName("label_2")
        self.verticalLayout.addWidget(self.label_2)

        self.retranslateUi(Dialog)
        QtCore.QMetaObject.connectSlotsByName(Dialog)

    def retranslateUi(self, Dialog):
        Dialog.setWindowTitle(QtGui.QApplication.translate("Dialog", "Dialog", None, QtGui.QApplication.UnicodeUTF8))
        self.label.setText(QtGui.QApplication.translate("Dialog", "UGLY", None, QtGui.QApplication.UnicodeUTF8))
        self.label_2.setText(QtGui.QApplication.translate("Dialog", "Not ugly", None, QtGui.QApplication.UnicodeUTF8))


if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    Dialog = QtGui.QDialog()
    ui = Ui_Dialog()
    ui.setupUi(Dialog)
    Dialog.show()
    sys.exit(app.exec_())

No more constraint on size: the label with font size 72 can be displayed.

from PyQt4 import QtCore, QtGui

class Ui_Dialog(object):
    def setupUi(self, Dialog):
        Dialog.setObjectName("Dialog")
        Dialog.resize(495, 140)
        self.verticalLayout = QtGui.QVBoxLayout(Dialog)
        self.verticalLayout.setObjectName("verticalLayout")
        self.label = QtGui.QLabel(Dialog)
        font = QtGui.QFont()
        font.setFamily("Andale Mono")
        font.setPointSize(72)
        self.label.setFont(font)
        self.label.setObjectName("label")
        self.verticalLayout.addWidget(self.label)
        self.label_2 = QtGui.QLabel(Dialog)
        self.label_2.setObjectName("label_2")
        self.verticalLayout.addWidget(self.label_2)

        self.retranslateUi(Dialog)
        QtCore.QMetaObject.connectSlotsByName(Dialog)

    def retranslateUi(self, Dialog):
        Dialog.setWindowTitle(QtGui.QApplication.translate("Dialog", "Dialog", None, QtGui.QApplication.UnicodeUTF8))
        self.label.setText(QtGui.QApplication.translate("Dialog", "less UGLY", None, QtGui.QApplication.UnicodeUTF8))
        self.label_2.setText(QtGui.QApplication.translate("Dialog", "Not ugly", None, QtGui.QApplication.UnicodeUTF8))


if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    Dialog = QtGui.QDialog()
    ui = Ui_Dialog()
    ui.setupUi(Dialog)
    Dialog.show()
    sys.exit(app.exec_())

Layouts cannot adjust the size of the outer widget, that still has to get set to the maximum size you know you will require — oggmonster, Jul 22 '13 at 08:22
@oggmonster if you don't manually restrict sizes of widgets (with qss or setMaximumXXX methods) and if you correctly use layouts - than all should be OK. Outer widgets should be also placed in layouts. — Dmitry Sazonov, Jul 22 '13 at 08:41
If your outer widget has a maximum size, you won't be able to deal with any font size. Either you define a maximum font size, either you release the size constraint of the outer widget. — Frodon, Jul 22 '13 at 08:50
@Frodon, could you provide small sample with "ugly" font sizes? — Dmitry Sazonov, Jul 22 '13 at 14:37

Making Qt Application that work with different System Font Sizes

1 Answers1