QGraphicsView and QGraphicsScene

[alisami]

Hi,

I have a problem about setting the rectangle size of the QGraphicsScene to QGraphicsView's visible part.

When I set the scene's rectangle using view's width and height, the scroll bars appear.

How can I determine the maximum visible size of the QGraphicsView so that I can set the scene's rectangle to maximum ?

The example code is below to demonstrate the problem:

#include <QApplication>
#include <QtGui>
#include <QDebug>
 
int main ( int argc, char *argv[] )
{
        QApplication app ( argc, argv );
 
        QGraphicsView view;
        view.setGeometry ( 10, 10, 400, 300 );
        view.setScene ( new QGraphicsScene() );
 
        qint32 gvWidth = view.width();
        qint32 gvHeight = view.height();
        view.setSceneRect ( -gvWidth / 2, -gvHeight / 2, gvWidth, gvHeight );
 
        QGraphicsLineItem* line = new QGraphicsLineItem ( - gvWidth / 2, - gvHeight / 2, gvWidth / 2, gvHeight / 2 );
        view.scene()->addItem ( line );
 
        view.show();
        return app.exec();
}

#include <QApplication>
#include <QtGui>
#include <QDebug>

int main ( int argc, char *argv[] )
{
        QApplication app ( argc, argv );

        QGraphicsView view;
        view.setGeometry ( 10, 10, 400, 300 );
        view.setScene ( new QGraphicsScene() );

        qint32 gvWidth = view.width();
        qint32 gvHeight = view.height();
        view.setSceneRect ( -gvWidth / 2, -gvHeight / 2, gvWidth, gvHeight );

        QGraphicsLineItem* line = new QGraphicsLineItem ( - gvWidth / 2, - gvHeight / 2, gvWidth / 2, gvHeight / 2 );
        view.scene()->addItem ( line );

        view.show();
        return app.exec();
}

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Sami

[wysota]

Use the viewport() rect of the view.

[alisami]

Actually, I have figured out that there is a problem about the viewport's size when using QMainWindow.

I have created a QMainWindow with a QMenuBar and a QGraphicsView on the central part of the QMainWindow.

When the QMenuBar is created and the `setMenuBar()` method of QMainWindow is called, the size of the resulting viewport of the view is not the same as the viewport's size (there is a 20-30 pixels difference). But if `setMenuBar()` method is not called, everything works just fine.

[wysota]

Are you sure it is not your fault? Maybe you are reading the size too early or something? I strongly doubt some external widget would have any influence on some other widget's internal widget.

[alisami]

wysota,

I hope it is my fault, as I couldn't figure out how to fix this problem.

Below are the files for the case. When commenting out the below line in QGuiMainScreen.cpp, the scrollbars disappears:

this->setMenuBar ( menuBar );

this->setMenuBar ( menuBar );

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QGuiMainScreen.h

#include <QMainWindow>
#include <QMenuBar>
#include <QGraphicsView>
 
class QGuiMainScreen: public QMainWindow
{
public:
        QGuiMainScreen();
        virtual void show();
 
private:
        QGraphicsView* m_gv;
};

#include <QMainWindow>
#include <QMenuBar>
#include <QGraphicsView>

class QGuiMainScreen: public QMainWindow
{
public:
        QGuiMainScreen();
        virtual void show();

private:
        QGraphicsView* m_gv;
};

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QGuiMainScreen.cpp

#include "QGuiMainScreen.h"
 
#include <QLayout>
#include <QGLWidget>
 
QGuiMainScreen::QGuiMainScreen() : QMainWindow()
{
        QWidget *centralwidget;
        QHBoxLayout *outerLayout;
        QMenuBar *menuBar;
        QMenu *menuSystem;
 
        this->resize ( 1024, 768 );
        centralwidget = new QWidget ( this );
        this->setCentralWidget ( centralwidget );
 
        menuBar = new QMenuBar ( this );
        menuBar->setGeometry ( QRect ( 0, 0, 1024, 30 ) );
        menuSystem = new QMenu ( menuBar );
        menuSystem->setTitle ( "System" );
        menuBar->addAction ( menuSystem->menuAction() );
        this->setMenuBar ( menuBar );
 
        outerLayout = new QHBoxLayout ( centralwidget );
        outerLayout->setSpacing ( 0 );
        outerLayout->setMargin ( 0 );
 
        m_gv = new QGraphicsView ( this );
        m_gv->setScene ( new QGraphicsScene() );
        outerLayout->insertWidget ( 0, m_gv, 1 );
}
 
void QGuiMainScreen::show()
{
        QMainWindow::show();
 
        m_gv->setViewport ( new QGLWidget() );
 
        qint32 sceneWidth = m_gv->viewport()->width();
        qint32 sceneHeight = m_gv->viewport()->height();
 
        m_gv->scene()->setSceneRect ( -sceneWidth / 2, -sceneHeight / 2, sceneWidth, sceneHeight );
}

#include "QGuiMainScreen.h"

#include <QLayout>
#include <QGLWidget>

QGuiMainScreen::QGuiMainScreen() : QMainWindow()
{
        QWidget *centralwidget;
        QHBoxLayout *outerLayout;
        QMenuBar *menuBar;
        QMenu *menuSystem;

        this->resize ( 1024, 768 );
        centralwidget = new QWidget ( this );
        this->setCentralWidget ( centralwidget );

        menuBar = new QMenuBar ( this );
        menuBar->setGeometry ( QRect ( 0, 0, 1024, 30 ) );
        menuSystem = new QMenu ( menuBar );
        menuSystem->setTitle ( "System" );
        menuBar->addAction ( menuSystem->menuAction() );
        this->setMenuBar ( menuBar );

        outerLayout = new QHBoxLayout ( centralwidget );
        outerLayout->setSpacing ( 0 );
        outerLayout->setMargin ( 0 );

        m_gv = new QGraphicsView ( this );
        m_gv->setScene ( new QGraphicsScene() );
        outerLayout->insertWidget ( 0, m_gv, 1 );
}

void QGuiMainScreen::show()
{
        QMainWindow::show();

        m_gv->setViewport ( new QGLWidget() );

        qint32 sceneWidth = m_gv->viewport()->width();
        qint32 sceneHeight = m_gv->viewport()->height();

        m_gv->scene()->setSceneRect ( -sceneWidth / 2, -sceneHeight / 2, sceneWidth, sceneHeight );
}

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main.cpp

#include <QApplication>
 
#include "QGuiMainScreen.h"
 
int main ( int argc, char *argv[] )
{
        QApplication app ( argc, argv );
 
        QGuiMainScreen myWnd;
        myWnd.show();
 
        return app.exec();
}

#include <QApplication>

#include "QGuiMainScreen.h"

int main ( int argc, char *argv[] )
{
        QApplication app ( argc, argv );

        QGuiMainScreen myWnd;
        myWnd.show();

        return app.exec();
}

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pro file

TEMPLATE = app
TARGET =
DEPENDPATH += .
INCLUDEPATH += .
QT += opengl
 
# Input
HEADERS += QGuiMainScreen.h
SOURCES += main.cpp QGuiMainScreen.cpp

TEMPLATE = app
TARGET =
DEPENDPATH += .
INCLUDEPATH += .
QT += opengl

# Input
HEADERS += QGuiMainScreen.h
SOURCES += main.cpp QGuiMainScreen.cpp

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Sami

[wysota]

First of all you don't have to create a menu bar yourself. If you call QMainWindow::menuBar() a menu bar will be created and setup for you. There is a chance this will already fix your problem.

[alisami]

Actually, the code is generated by uic and I just copied the generated code to demonstrate the problem.

So when I call `setupUi()` the problem occurs.

[alisami]

wysota,

I also tried to create the menubar by using QMainWindow::menuBar() but again the viewport do not have the correct size and the problem persists.

sami

[alisami]

Hi,

It is confirmed by Qt support that this is bug related to the menubar.

Yeah, looks like this is a bug because QMenuBar is reporting it's size wrong as a height of 2 pixels instead of 30 for some reason.

wysota,
Thanks for your interest.