pyqt checkbox resolution for different scales

andverdu

I am developing a windows app with pyside6. I have a QTableView and have used a QItemDelegate to add checkboxes to the table. The checkboxes are drawn in the paint method of the QItemDelegate, using the method drawCheck

class CheckBoxDelegate(QItemDelegate):
    """
    A delegate that places a fully functioning QCheckBox cell of the column to which it's applied.
    """
    def __init__(self, parent):
        QItemDelegate.__init__(self, parent)

    def createEditor(self, parent, option, index):
        """
        Important, otherwise an editor is created if the user clicks in this cell.
        """
        return None

    def paint(self, painter, option, index):
        """
        Paint a checkbox without the label.
        """
        value = int(index.data())
        if value == 0:
            value = Qt.Unchecked
        else:
            value = Qt.Checked
        self.drawCheck(painter, option, option.rect, value)

    def editorEvent(self, event, model, option, index):
        """
        Change the data in the model and the state of the checkbox
        if the user presses the left mousebutton and this cell is editable. Otherwise do nothing.
        """
        if not int(index.flags() & Qt.ItemIsEditable) > 0:
            return False

        if event.type() == QEvent.MouseButtonRelease and event.button() == Qt.LeftButton:
            # Change the checkbox-state
            self.setModelData(None, model, index)
            return True

        return False

    def setModelData(self, editor, model, index):
        """
        Set new data in the model
        """
        model.setData(index, 1 if int(index.data()) == 0 else 0, Qt.EditRole)

The problem is that the checkboxes are only correctly displayed if the scale is set at 100%. Changing it to 125% or more, makes the checkbox too big and the icon inside blurry (images below)

checkboxes at 125%
checkboxes at 100%

I have tried different settings for scaling the app. The combination of settings that works to scale the rest of the application is:

os.environ["QT_ENABLE_HIGHDPI_SCALING"] = "0"
os.environ["QT_FONT_DPI"] = "96"
os.environ["QT_SCALE_FACTOR"] = "1"
QApplication.setHighDpiScaleFactorRoundingPolicy(QtCore.Qt.HighDpiScaleFactorRoundingPolicy.Floor)

Still changing these settings has no effect on the checkboxes resolution

andverdu

Issue solved by implementing the checkboxes through Qt.ItemIsUserCheckable, rather than through a delegate

friedemannkleint

Which Qt version is this ? - This should improve in recent versions due to https://bugreports.qt.io/browse/QTBUG-86344 .

andverdu

I am using PySide6 version 6.2.1

friedemannkleint

Please try the recent version (6.4.2/6.5.0).

andverdu

@friedemannkleint Thanks for your suggestion, I have tested with pyside 6.4.2 and the issue persists, do you have any other idea on how to solve this?

friedemannkleint

You can avoid fractional scale factor rounding by setting

QGuiApplication.setHighDpiScaleFactorRoundingPolicy(Qt.HighDpiScaleFactorRoundingPolicy.Round)

If it differs from a normal QCheckBox, I would file a bug under QTBUG (see also https://bugreports.qt.io/browse/QTBUG-86344 ).

andverdu

Issue solved by implementing the checkboxes through Qt.ItemIsUserCheckable, rather than through a delegate