Question

Is it possible to scale (or “zoom”) a QTextEdit area? I believe I read that placing QTextEdit inside QLayout can allow for scaling of the QTextEdit area, though did not find how to implement it. Couple of options…

CTRL + Roll of Mouse Wheel
Running the code below, holding down the CTRL (control) key and rolling the mouse wheel, the event is captured and the text does scale (at least on Windows), however, as the text grows larger the wheel has to move further and further for very much effect, so one goal is to be able to modify that somehow, maybe some math to increase the increments to a greater degree on increases in the plus direction.

(The setReadOnly()’s below are because it would seem textEdit has to be ReadOnly(False) for the mouse event to be captured, then True to be able to scale during roll of the mouse wheel, so it is then set back to original state of False again on release of the CTRL key).

Toolbar Button Click
The other option is toolbar buttons for zoom in and out.
onZoomInClicked() is called.

Some current problems with the code below
1. It prints: QLayout: Attempting to add QLayout "" to MainWindow "", which already has a layout and I don’t have my head wrapped around that yet.
2. QtGui.QTextEdit(self.formLayout) instead of (self) to place the textEdit area inside the layout produces TypeError: 'PySide.QtGui.QTextEdit' called with wrong argument types
3. wheelEvent() could use some way to modify event.delta() maybe?
4. The toolbar button (text only) will currently run its def when clicked, however it only contains a print statement.

from PySide import QtGui, QtCore

class MainWindow(QtGui.QMainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)

        self.formLayout   = QtGui.QFormLayout(self)
        self.textEdit     = QtGui.QTextEdit(self)
        self.toolBar      = QtGui.QToolBar(self)
        self.actionZoomIn = QtGui.QAction(self)
        self.textEdit.setHtml('<font color=blue>Hello <b>world</b></font>')
        self.setCentralWidget(self.textEdit)
        self.addToolBar(self.toolBar)
        self.toolBar.addAction(self.actionZoomIn)
        self.actionZoomIn.setText('Zoom In')
        self.actionZoomIn.connect(self.actionZoomIn,
            QtCore.SIGNAL('triggered()'), self.onZoomInClicked)

    def onZoomInClicked(self):
        print "onZoomInClicked(self) needs code"

    def wheelEvent(self, event):
        print "wheelEvent() captured"
        if (event.modifiers() & QtCore.Qt.ControlModifier):
            self.textEdit.setReadOnly(True)

            event.accept()            

    def keyReleaseEvent(self, evt):
        if evt.key() == QtCore.Qt.Key_Control:
            self.textEdit.setReadOnly(False)

if __name__ == '__main__':
    app   = QtGui.QApplication([])
    frame = MainWindow()
    frame.show()
    app.exec_()

I’ve been grappling with this for days so would be great to have the more customizable QTextEdit scale/zoom working if it is even possible.

Answer 1

The two error messages can be expained as follows:

1. The QMainWidget automatically gets a layout, so the QFormLayout is redundant. If you want to add a layout, create a QWidget to be the central widget and make it the parent of the new layout. Other widgets can then be added to that new layout.
2. The parent of a QWidget subclass must itself be QWidget subclass, which QFormLayout isn’t.

I’ve modified your example so that it does most of what you asked for. Note that QTextEdit.zoomIn and QTextEdit.zoomOut both take a range argument for controlling the degree of zoom.

from PySide import QtGui, QtCore

class MainWindow(QtGui.QMainWindow):
    def __init__(self, parent=None):
        super(MainWindow, self).__init__(parent)
        self.textEdit = Editor(self)
        self.toolBar = QtGui.QToolBar(self)
        self.actionZoomIn = QtGui.QAction('Zoom In', self)
        self.actionZoomOut = QtGui.QAction('Zoom Out', self)
        self.textEdit.setHtml('<font color=blue>Hello <b>world</b></font>')
        self.setCentralWidget(self.textEdit)
        self.addToolBar(self.toolBar)
        self.toolBar.addAction(self.actionZoomIn)
        self.toolBar.addAction(self.actionZoomOut)
        self.actionZoomIn.triggered.connect(self.onZoomInClicked)
        self.actionZoomOut.triggered.connect(self.onZoomOutClicked)

    def onZoomInClicked(self):
        self.textEdit.zoom(+1)

    def onZoomOutClicked(self):
        self.textEdit.zoom(-1)

class Editor(QtGui.QTextEdit):
    def __init__(self, parent=None):
        super(Editor, self).__init__(parent)

    def zoom(self, delta):
        if delta < 0:
            self.zoomOut(1)
        elif delta > 0:
            self.zoomIn(5)

    def wheelEvent(self, event):
        if (event.modifiers() & QtCore.Qt.ControlModifier):
            self.zoom(event.delta())
        else:
            QtGui.QTextEdit.wheelEvent(self, event)

if __name__ == '__main__':

    import sys
    app = QtGui.QApplication(sys.argv)
    window = MainWindow()
    window.show()
    app.exec_()