Implementing resize handles on QRubberband? Is QSizeGrip relevant?

Question

I'd like to make my QRubberband instance user resizeable. I've seen this question here but there isn't a solution.

The use case is that the user can drag out a selection marquee over a photo and then make fine adjustments by dragging on the QRubberband margins to change geometry, or reposition existing geometry by dragging the selection. I have the repositioning implemented but I am wondering about resize handles for changing the geometry of the QRubberband.

Is it possible to use QSizeGrip here? Barring that, is there a standard way of checking for mouse-within-margin type events within Qt or some other way to implement this? This is for a research app that doesn't need or warrant lots of effort on this feature but it would be good to have.

Answer 1

Yes, it's possible. Here is the implementation:

Header:

class Resizable_rubber_band : public QWidget {
public:
  Resizable_rubber_band(QWidget* parent = 0);

private:
  QRubberBand* rubberband;
  void resizeEvent(QResizeEvent *);

};

Source:

Resizable_rubber_band::Resizable_rubber_band(QWidget *parent) : QWidget(parent) {
  //tell QSizeGrip to resize this widget instead of top-level window
  setWindowFlags(Qt::SubWindow);
  QHBoxLayout* layout = new QHBoxLayout(this);
  layout->setContentsMargins(0, 0, 0, 0);
  QSizeGrip* grip1 = new QSizeGrip(this);
  QSizeGrip* grip2 = new QSizeGrip(this);
  layout->addWidget(grip1, 0, Qt::AlignLeft | Qt::AlignTop);
  layout->addWidget(grip2, 0, Qt::AlignRight | Qt::AlignBottom);
  rubberband = new QRubberBand(QRubberBand::Rectangle, this);
  rubberband->move(0, 0);
  rubberband->show();
  show();
}

void Resizable_rubber_band::resizeEvent(QResizeEvent *) {
  rubberband->resize(size());
}

Usage: (ui->label is the label used for displaying the image to be cropped)

Resizable_rubber_band* band = new Resizable_rubber_band(ui->label);
band->move(100, 100);
band->resize(50, 50);
band->setMinimumSize(30, 30);

Answer 2

In case anyone else wanders in here off Google with the intent to use this with PyQt, here's the equivalent Python code to @pavel-strakhov's C++ example and I can confirm that it works for me on *buntu Linux 14.04 LTS with the system-provided Python 3.4 and PyQt 5.2.1.

(With the caveat that my chosen widget theme doesn't know how to rotate the QSizeGrip in the top-left corner, so both corners have identical-looking grips.)

Source:

class ResizableRubberBand(QWidget):
    """Wrapper to make QRubberBand mouse-resizable using QSizeGrip

    Source: http://stackoverflow.com/a/19067132/435253
    """
    def __init__(self, parent=None):
        super(ResizableRubberBand, self).__init__(parent)

        self.setWindowFlags(Qt.SubWindow)
        self.layout = QHBoxLayout(self)
        self.layout.setContentsMargins(0, 0, 0, 0)

        self.grip1 = QSizeGrip(self)
        self.grip2 = QSizeGrip(self)
        self.layout.addWidget(self.grip1, 0, Qt.AlignLeft | Qt.AlignTop)
        self.layout.addWidget(self.grip2, 0, Qt.AlignRight | Qt.AlignBottom)

        self.rubberband = QRubberBand(QRubberBand.Rectangle, self)
        self.rubberband.move(0, 0)
        self.rubberband.show()
        self.show()

    def resizeEvent(self, event):
        self.rubberband.resize(self.size())

Usage:

self.band = ResizableRubberBand(ui.label)
self.band.move(100, 100)
self.band.resize(50, 50)
self.band.setMinimumSize(30, 30)