Qt: Resize borderless widget

Question

My question is basically the same as this one, but applied to the Qt C++ framework.

I am implementing a popup window by inheriting QWidget with flags Qt::QPopup | Qt::QWindow. I would like this window to be moveable and resizeable, I'm currently achieving this by using the mouse events in the following code:

void TextPopup::mousePressEvent(QMouseEvent* event)
{
    offset = event->pos();
    QWidget::mousePressEvent(event);
}

void TextPopup::mouseMoveEvent(QMouseEvent* event)
{
    if(event->buttons() & Qt::LeftButton)
        if(resizeMode) {
            QPoint p = mapToGlobal(event->pos()) - geometry().topLeft();
            resize(p.x(), p.y());
        } else
            move(mapToParent(event->pos() - offset));
    else {
        QPoint diff = geometry().bottomRight() - mapToGlobal(event->pos());
        if(diff.x() <= 6 && diff.y() <= 6) {
            if(!resizeMode) {
                setCursor(Qt::SizeFDiagCursor);
                resizeMode = true;
            }
        } else {
            if(resizeMode) {
                setCursor(Qt::SizeAllCursor);
                resizeMode = false;
            }
        }
    }
}

void TextPopup::mouseReleaseEvent(QMouseEvent* event)
{
    offset = QPoint();
    QWidget::mouseReleaseEvent(event);
}

I have a few problems with this. For one, I'm guessing there's a better way to do it. And more importantly, I would like the resize symbol at the bottom right as in this image] (taken from the post mentioned above). Any suggestions for achieving this?

Germiston

I'm sure you're aware of this, but others reading this might not be. The documentation on Qt borderless windows states that "The user cannot move or resize a borderless window via the window system." – Barringer

Answer 1

You can add the resize grip by calling QDialog's or QStatusBar's function setSizeGripEnabled (or directly in QtCreator form designer).

For custom widgets the simplest way probably is to use QSizeGrip. I didn't use it myself but you can check the Qt source code on git for QStatusBar or QDialog.

Stabile

Hey thanks, this seems to work. I'm having some problems with the QSizeGrip class, but at least it is providing the functionality. – Germiston

Answer 2

If you don't want QSizeGrip you may take a look at this solution :

frameless.h:

#pragma once
#include <QtWidgets/QWidget>
#include <QtWidgets/QRubberBand>
#include <QtCore/QObject>
#include <QtCore/QEvent>
#include <QtCore/QRect>
#include <QtCore/QPoint>
#include <QtCore/Qt>
#include <QtGui/QHoverEvent>
#include <QtGui/QMouseEvent>

class FrameLess : public QObject {
    Q_OBJECT

public:
    enum Edge {
        None = 0x0,
        Left = 0x1,
        Top = 0x2,
        Right = 0x4,
        Bottom = 0x8,
        TopLeft = 0x10,
        TopRight = 0x20,
        BottomLeft = 0x40,
        BottomRight = 0x80,
    };
    Q_ENUM(Edge);
    Q_DECLARE_FLAGS(Edges, Edge);

    FrameLess(QWidget *target);

    void setBorderWidth(int w) {
        _borderWidth = w;
    }
    int borderWidth() const {
        return _borderWidth;
    }

protected:
    bool eventFilter(QObject *o, QEvent *e) override;
    void mouseHover(QHoverEvent*);
    void mouseLeave(QEvent*);
    void mousePress(QMouseEvent*);
    void mouseRealese(QMouseEvent*);
    void mouseMove(QMouseEvent*);
    void updateCursorShape(const QPoint &);
    void calculateCursorPosition(const QPoint &, const QRect &, Edges &);

private:
    QWidget *_target = nullptr;
    QRubberBand *_rubberband = nullptr;
    bool _cursorchanged;
    bool _leftButtonPressed;
    Edges _mousePress = Edge::None;
    Edges _mouseMove = Edge::None;
    int _borderWidth;

    QPoint _dragPos;
    bool _dragStart = false;
};

Q_DECLARE_OPERATORS_FOR_FLAGS(FrameLess::Edges);

frameless.cpp:

#include "frameless.h"

FrameLess::FrameLess(QWidget *target) :
    _target(target),
    _cursorchanged(false),
    _leftButtonPressed(false),
    _borderWidth(5),
    _dragPos(QPoint())
{
    _target->setMouseTracking(true);
    _target->setWindowFlags(Qt::FramelessWindowHint);
    _target->setAttribute(Qt::WA_Hover);
    _target->installEventFilter(this);
    _rubberband = new QRubberBand(QRubberBand::Rectangle);
}

bool FrameLess::eventFilter(QObject *o, QEvent*e) {
    if (e->type() == QEvent::MouseMove ||
        e->type() == QEvent::HoverMove ||
        e->type() == QEvent::Leave ||
        e->type() == QEvent::MouseButtonPress ||
        e->type() == QEvent::MouseButtonRelease) {

        switch (e->type()) {
        case QEvent::MouseMove:
            mouseMove(static_cast<QMouseEvent*>(e));
            return true;
            break;
        case QEvent::HoverMove:
            mouseHover(static_cast<QHoverEvent*>(e));
            return true;
            break;
        case QEvent::Leave:
            mouseLeave(e);
            return true;
            break;
        case QEvent::MouseButtonPress:
            mousePress(static_cast<QMouseEvent*>(e));
            return true;
            break;
        case QEvent::MouseButtonRelease:
            mouseRealese(static_cast<QMouseEvent*>(e));
            return true;
            break;
        }
    }
    else {
        return _target->eventFilter(o, e);
    }
}

void FrameLess::mouseHover(QHoverEvent *e) {
    updateCursorShape(_target->mapToGlobal(e->pos()));
}

void FrameLess::mouseLeave(QEvent *e) {
    if (!_leftButtonPressed) {
        _target->unsetCursor();
    }
}

void FrameLess::mousePress(QMouseEvent *e) {
    if (e->button() & Qt::LeftButton) {
        _leftButtonPressed = true;
        calculateCursorPosition(e->globalPos(), _target->frameGeometry(), _mousePress);
        if (!_mousePress.testFlag(Edge::None)) {
            _rubberband->setGeometry(_target->frameGeometry());
        }
        if (_target->rect().marginsRemoved(QMargins(borderWidth(), borderWidth(), borderWidth(), borderWidth())).contains(e->pos())) {
            _dragStart = true;
            _dragPos = e->pos();
        }
    }
}

void FrameLess::mouseRealese(QMouseEvent *e) {
    if (e->button() & Qt::LeftButton) {
        _leftButtonPressed = false;
        _dragStart = false;
    }
}

void FrameLess::mouseMove(QMouseEvent *e) {
    if (_leftButtonPressed) {
        if (_dragStart) {
            _target->move(_target->frameGeometry().topLeft() + (e->pos() - _dragPos));
        }

        if (!_mousePress.testFlag(Edge::None)) {
            int left = _rubberband->frameGeometry().left();
            int top = _rubberband->frameGeometry().top();
            int right = _rubberband->frameGeometry().right();
            int bottom = _rubberband->frameGeometry().bottom();
            switch (_mousePress) {
            case Edge::Top:
                top = e->globalPos().y();
                break;
            case Edge::Bottom:
                bottom = e->globalPos().y();
                break;
            case Edge::Left:
                left = e->globalPos().x();
                break;
            case Edge::Right:
                right = e->globalPos().x();
                break;
            case Edge::TopLeft:
                top = e->globalPos().y();
                left = e->globalPos().x();
                break;
            case Edge::TopRight:
                right = e->globalPos().x();
                top = e->globalPos().y();
                break;
            case Edge::BottomLeft:
                bottom = e->globalPos().y();
                left = e->globalPos().x();
                break;
            case Edge::BottomRight:
                bottom = e->globalPos().y();
                right = e->globalPos().x();
                break;
            }
            QRect newRect(QPoint(left, top), QPoint(right, bottom));
            if (newRect.width() < _target->minimumWidth()) {
                left = _target->frameGeometry().x();
            }
            else if (newRect.height() < _target->minimumHeight()) {
                top = _target->frameGeometry().y();
            }
            _target->setGeometry(QRect(QPoint(left, top), QPoint(right, bottom)));
            _rubberband->setGeometry(QRect(QPoint(left, top), QPoint(right, bottom)));
        }
    }
    else {
        updateCursorShape(e->globalPos());
    }
}

void FrameLess::updateCursorShape(const QPoint &pos) {
    if (_target->isFullScreen() || _target->isMaximized()) {
        if (_cursorchanged) {
            _target->unsetCursor();
        }
        return;
    }
    if (!_leftButtonPressed) {
        calculateCursorPosition(pos, _target->frameGeometry(), _mouseMove);
        _cursorchanged = true;
        if (_mouseMove.testFlag(Edge::Top) || _mouseMove.testFlag(Edge::Bottom)) {
            _target->setCursor(Qt::SizeVerCursor);
        }
        else if (_mouseMove.testFlag(Edge::Left) || _mouseMove.testFlag(Edge::Right)) {
            _target->setCursor(Qt::SizeHorCursor);
        }
        else if (_mouseMove.testFlag(Edge::TopLeft) || _mouseMove.testFlag(Edge::BottomRight)) {
            _target->setCursor(Qt::SizeFDiagCursor);
        }
        else if (_mouseMove.testFlag(Edge::TopRight) || _mouseMove.testFlag(Edge::BottomLeft)) {
            _target->setCursor(Qt::SizeBDiagCursor);
        }
        else if (_cursorchanged) {
            _target->unsetCursor();
            _cursorchanged = false;
        }
    }
}

void FrameLess::calculateCursorPosition(const QPoint &pos, const QRect &framerect, Edges &_edge) {
    bool onLeft = pos.x() >= framerect.x() - _borderWidth && pos.x() <= framerect.x() + _borderWidth &&
        pos.y() <= framerect.y() + framerect.height() - _borderWidth && pos.y() >= framerect.y() + _borderWidth;

    bool onRight = pos.x() >= framerect.x() + framerect.width() - _borderWidth && pos.x() <= framerect.x() + framerect.width() &&
        pos.y() >= framerect.y() + _borderWidth && pos.y() <= framerect.y() + framerect.height() - _borderWidth;

    bool onBottom = pos.x() >= framerect.x() + _borderWidth && pos.x() <= framerect.x() + framerect.width() - _borderWidth  &&
        pos.y() >= framerect.y() + framerect.height() - _borderWidth && pos.y() <= framerect.y() + framerect.height();

    bool onTop = pos.x() >= framerect.x() + _borderWidth && pos.x() <= framerect.x() + framerect.width() - _borderWidth &&
        pos.y() >= framerect.y() && pos.y() <= framerect.y() + _borderWidth;

    bool  onBottomLeft = pos.x() <= framerect.x() + _borderWidth && pos.x() >= framerect.x() &&
        pos.y() <= framerect.y() + framerect.height() && pos.y() >= framerect.y() + framerect.height() - _borderWidth;

    bool onBottomRight = pos.x() >= framerect.x() + framerect.width() - _borderWidth && pos.x() <= framerect.x() + framerect.width() &&
        pos.y() >= framerect.y() + framerect.height() - _borderWidth && pos.y() <= framerect.y() + framerect.height();

    bool onTopRight = pos.x() >= framerect.x() + framerect.width() - _borderWidth && pos.x() <= framerect.x() + framerect.width() &&
        pos.y() >= framerect.y() && pos.y() <= framerect.y() + _borderWidth;

    bool onTopLeft = pos.x() >= framerect.x() && pos.x() <= framerect.x() + _borderWidth &&
        pos.y() >= framerect.y() && pos.y() <= framerect.y() + _borderWidth;

    if (onLeft) {
        _edge = Left;
    }
    else if (onRight) {
        _edge = Right;
    }
    else if (onBottom) {
        _edge = Bottom;
    }
    else if (onTop) {
        _edge = Top;
    }
    else if (onBottomLeft) {
        _edge = BottomLeft;
    }
    else if (onBottomRight) {
        _edge = BottomRight;
    }
    else if (onTopRight) {
        _edge = TopRight;
    }
    else if (onTopLeft) {
        _edge = TopLeft;
    }
    else {
        _edge = None;
    }
}

And just create an instance and put your QWidget:

#include "frameless.h"
#include <QtWidgets/qapplication.h>

int main(int argc, char *argv[]) {
    QApplication a(argc, argv);
    QWidget *widget = new QWidget;
    FrameLess f(widget);
    widget->show();
    return a.exec();
}

Mania

Answer 3

You can use QSizeGrip in a layout inside your widget :

myWidget->setWindowFlags(Qt::SubWindow);

QSizeGrip * sizeGrip = new QSizeGrip(myWidget);

QGridLayout * layout = new QGridLayout(myWidget);
layout->addWidget(sizeGrip, 0,0,1,1,Qt::AlignBottom | Qt::AlignRight);

The QSizeGrip class provides a resize handle for resizing top-level windows. When you set the widget flag Qt::SubWindow, then the user can resize it using the size grip.

Eleen