keyboard and openGL widget

**21did21** · 5th July 2011, 11:54

Hello world,

i use openGL widget and i want to use keybord to rotate my object but it don't works...

i don't know why, because i think that my programm is good...

can you see this please? :

MAIN.CPP

Qt Code:

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#include <iostream>   
#include <QApplication>
#include "myGLWidget.h"
#include <QGridLayout>
#include "FenPrincipale.h"
 
using namespace std;
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    FenPrincipale fenetre;
    fenetre.showMaximized();
    fenetre.setWindowTitle("blabla");
    return app.exec();
}

#include <iostream>   
#include <QApplication>
#include "myGLWidget.h"
#include <QGridLayout>
#include "FenPrincipale.h"

using namespace std;
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    FenPrincipale fenetre;
    fenetre.showMaximized();
    fenetre.setWindowTitle("blabla");
    return app.exec();
}

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FenPrincipale.f

Qt Code:

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#ifndef HEADER_FENPRINCIPALE
#define HEADER_FENPRINCIPALE
#include <QtGui>
class FenPrincipale : public QMainWindow
{
        public:
                FenPrincipale();
                ~FenPrincipale();
        private:
};
#endif

#ifndef HEADER_FENPRINCIPALE
#define HEADER_FENPRINCIPALE
#include <QtGui>
class FenPrincipale : public QMainWindow
{
        public:
                FenPrincipale();
                ~FenPrincipale();
        private:
};
#endif

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FenPrincipale.CPP

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#include "FenPrincipale.h"
#include "myGLWidget.h"
FenPrincipale::FenPrincipale()
{
    QMdiArea *zoneCentrale = new QMdiArea;
    myGLWidget *plotFenetre = new myGLWidget;
    QMdiSubWindow *sousFenetre1 = zoneCentrale->addSubWindow(plotFenetre);
    setCentralWidget(zoneCentrale);
}
FenPrincipale::~FenPrincipale()
{
}

#include "FenPrincipale.h"
#include "myGLWidget.h"
FenPrincipale::FenPrincipale()
{
    QMdiArea *zoneCentrale = new QMdiArea;
    myGLWidget *plotFenetre = new myGLWidget;
    QMdiSubWindow *sousFenetre1 = zoneCentrale->addSubWindow(plotFenetre);
    setCentralWidget(zoneCentrale);
}
FenPrincipale::~FenPrincipale()
{
}

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MAIN.CPP

Qt Code:

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#include <iostream>   
#include <QApplication>
#include "myGLWidget.h"
#include <QGridLayout>
#include "FenPrincipale.h"
 
using namespace std;
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    FenPrincipale fenetre;
    fenetre.showMaximized();
    fenetre.setWindowTitle("blabla");
    return app.exec();
}

#include <iostream>   
#include <QApplication>
#include "myGLWidget.h"
#include <QGridLayout>
#include "FenPrincipale.h"

using namespace std;
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    FenPrincipale fenetre;
    fenetre.showMaximized();
    fenetre.setWindowTitle("blabla");
    return app.exec();
}

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myGLWidget.H

Qt Code:

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#ifndef MYGLWIDGET_H
#define MYGLWIDGET_H
#include <QtOpenGL>
#include <QGLWidget>
#include <QKeyEvent>
class myGLWidget : public QGLWidget //this class herite from QGLWidget
{
Q_OBJECT
public:
    myGLWidget();
    ~myGLWidget();
    void initializeGL();
    void resizeGL(int,int);
    void paintGL();
    void keyPressEvent( QKeyEvent *keyEvent );
 
public slots:
 
private:
    float rotateX;
    float rotateY;
    float rotateZ;
};
#endif // MYGLWIDGET_H

#ifndef MYGLWIDGET_H
#define MYGLWIDGET_H
#include <QtOpenGL>
#include <QGLWidget>
#include <QKeyEvent>
class myGLWidget : public QGLWidget //this class herite from QGLWidget
{
Q_OBJECT
public:
    myGLWidget();
    ~myGLWidget();
    void initializeGL();
    void resizeGL(int,int);
    void paintGL();
    void keyPressEvent( QKeyEvent *keyEvent );

public slots:

private:
    float rotateX;
    float rotateY;
    float rotateZ;
};
#endif // MYGLWIDGET_H

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myGLWidget.CPP

Qt Code:

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#include <iostream>        
#include "myGLWidget.h"
#include <GL/gl.h>
#include <GL/glu.h>
using namespace std;
myGLWidget::myGLWidget() : QGLWidget()
{
 
}
myGLWidget::~myGLWidget()
{
 
}
void myGLWidget::keyPressEvent(QKeyEvent *keyEvent)
{
    cout << "clavier" << endl;
    if (keyEvent->key())
    {
        if (Qt::Key_Up)
        {
            rotateX=rotateX+2;
            repaint();
            updateGL();
            cout << "UP" << endl;
        }
    }
    else
    {
    }
}
void myGLWidget::initializeGL() 
{
    glShadeModel(GL_SMOOTH);
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClearDepth(1.0f); 
    glEnable(GL_DEPTH_TEST); 
    glDepthFunc(GL_LEQUAL); 
    glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
}
void myGLWidget::resizeGL(int width, int height) 
{
    if(height == 0)
    height = 1;
    glViewport(0, 0, width, height);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45.0f, (GLfloat)width/(GLfloat)height, 0.1f, 100.0f);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}
void myGLWidget::paintGL()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glClearColor(1.0f,1.0f,1.0f,1.0f);
    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity( );
    gluLookAt( 1.2, 1.7, 1.0, 0, 0, 0, 0, 0, 1);
    glPushMatrix( ); 
    glRotatef(rotateX,1.0f,0.0f,0.0f); 
    glRotatef(rotateY,0.0f,1.0f,0.0f);
    glRotatef(rotateZ,0.0f,0.0f,1.0f);
    glBegin(GL_LINES); 
        //i draw
    glEnd();
}

#include <iostream>        
#include "myGLWidget.h"
#include <GL/gl.h>
#include <GL/glu.h>
using namespace std;
myGLWidget::myGLWidget() : QGLWidget()
{

}
myGLWidget::~myGLWidget()
{

}
void myGLWidget::keyPressEvent(QKeyEvent *keyEvent)
{
    cout << "clavier" << endl;
    if (keyEvent->key())
    {
        if (Qt::Key_Up)
        {
            rotateX=rotateX+2;
            repaint();
            updateGL();
            cout << "UP" << endl;
        }
    }
    else
    {
    }
}
void myGLWidget::initializeGL() 
{
    glShadeModel(GL_SMOOTH);
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClearDepth(1.0f); 
    glEnable(GL_DEPTH_TEST); 
    glDepthFunc(GL_LEQUAL); 
    glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
}
void myGLWidget::resizeGL(int width, int height) 
{
    if(height == 0)
    height = 1;
    glViewport(0, 0, width, height);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45.0f, (GLfloat)width/(GLfloat)height, 0.1f, 100.0f);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}
void myGLWidget::paintGL()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glClearColor(1.0f,1.0f,1.0f,1.0f);
    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity( );
    gluLookAt( 1.2, 1.7, 1.0, 0, 0, 0, 0, 0, 1);
    glPushMatrix( ); 
    glRotatef(rotateX,1.0f,0.0f,0.0f); 
    glRotatef(rotateY,0.0f,1.0f,0.0f);
    glRotatef(rotateZ,0.0f,0.0f,1.0f);
    glBegin(GL_LINES); 
        //i draw
    glEnd();
}

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EDIT:
2Â°) i have a second question:

you can see in this programm that i never tell the methode : "paintGL()"

but openGL nevertheless draw when i compile my project, why?

**stampede** · 5th July 2011, 12:02

First of all, you should initialize member variables rotateX, rotateY and rotateZ in constructor (set them to 0), because without it they will contain random values. Print them to see it yourself.
Second thing, this code :

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if (keyEvent->key())
    {
        if (Qt::Key_Up)
        {
            rotateX=rotateX+2;
            repaint();
            updateGL();
            cout << "UP" << endl;
        }
}

if (keyEvent->key())
    {
        if (Qt::Key_Up)
        {
            rotateX=rotateX+2;
            repaint();
            updateGL();
            cout << "UP" << endl;
        }
}

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is wrong. You should check if keyEvent->key() == Qt::Key_Up, not the two things separately.

but openGL nevertheless draw when i compile my project, why?

Because paintGL is called automatically when gl widget receives paintEvent.

**mcosta** · 5th July 2011, 12:02

This is your code.

Qt Code:

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void myGLWidget::keyPressEvent(QKeyEvent *keyEvent)
{
    cout << "clavier" << endl;
    if (keyEvent->key())
    {
        if (Qt::Key_Up)
        {
            rotateX=rotateX+2;
            repaint();
            updateGL();
            cout << "UP" << endl;
        }
    }
    else
    {
    }
}

void myGLWidget::keyPressEvent(QKeyEvent *keyEvent)
{
    cout << "clavier" << endl;
    if (keyEvent->key())
    {
        if (Qt::Key_Up)
        {
            rotateX=rotateX+2;
            repaint();
            updateGL();
            cout << "UP" << endl;
        }
    }
    else
    {
    }
}

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Try this code

Qt Code:

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void myGLWidget::keyPressEvent(QKeyEvent *keyEvent)
{
    cout << "clavier" << endl;
    if (keyEvent->key() == Qt::Key_Up) {
        rotateX=rotateX+2;
        updateGL();
        cout << "UP" << endl;
        keyEvent->accept();
    }
    else
        keyEvent->ignore();
}

void myGLWidget::keyPressEvent(QKeyEvent *keyEvent)
{
    cout << "clavier" << endl;
    if (keyEvent->key() == Qt::Key_Up) {
        rotateX=rotateX+2;
        updateGL();
        cout << "UP" << endl;
        keyEvent->accept();
    }
    else
        keyEvent->ignore();
}

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**21did21** · 5th July 2011, 13:27

thank for you help but it still don't works:

=> my problem it's not here, my problem is due to my programm never go in the function:

Qt Code:

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void myGLWidget::keyPressEvent(QKeyEvent *keyEvent)

void myGLWidget::keyPressEvent(QKeyEvent *keyEvent)

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i see this because i have put a "cout" in this function and this cout never show the keyword: "clavier"

=> if think i have a mistake a the management of keybord but i don't find it...
perhaps i have forgotten diffÃ©rents "#include " ???

=> can you try my code on your computer and say if it show the keyword "clavier" in your console?

thanks a lot

**meazza** · 5th July 2011, 14:01

Check out these functions from QWidget class.

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Qt::FocusPolicy	focusPolicy () const
void	setFocusPolicy ( Qt::FocusPolicy policy )

Qt::FocusPolicy	focusPolicy () const
void	setFocusPolicy ( Qt::FocusPolicy policy )

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Because by default a widget has Qt::NoFocus flag set.

**21did21** · 5th July 2011, 14:06

thank for your answer but i haven't understand because my english is not good

can you reformulate that i have to do this this function ?

**meazza** · 5th July 2011, 14:12

just try

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this->setFocusPolicy(Qt::StrongFocus)

this->setFocusPolicy(Qt::StrongFocus)

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Call this in the constructor of the item.

Qt Code:

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myGLWidget::myGLWidget() : QGLWidget()
{
       this->setFocusPolicy(Qt::StrongFocus)
}

myGLWidget::myGLWidget() : QGLWidget()
{
       this->setFocusPolicy(Qt::StrongFocus)
}

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like this

**john_god** · 5th July 2011, 14:14

what happens if in your main window instead of

Qt Code:

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FenPrincipale fenetre;
fenetre.showMaximized();

FenPrincipale fenetre;
fenetre.showMaximized();

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you use

Qt Code:

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myGLWidget fenetre;
fenetre.showMaximized();

myGLWidget fenetre;
fenetre.showMaximized();

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?

**peace_comp** · 5th July 2011, 14:20

Hi,
The Qt::FocusPolicy property holds the way the widget accepts keyboard focus (http://doc.qt.nokia.com/latest/qwidg...cusPolicy-prop)
to enable keyboard focus, add a call to setFocusPolicy(Qt::StrongFocus) in the widget constructor :

myGLWidget::myGLWidget() : QGLWidget()
{
setFocusPolicy(Qt::StrongFocus);
}

**21did21** · 5th July 2011, 14:23

Originally Posted by meazza

just try

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this->setFocusPolicy(Qt::StrongFocus)

this->setFocusPolicy(Qt::StrongFocus)

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Call this in the constructor of the item.

Qt Code:

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myGLWidget::myGLWidget() : QGLWidget()
{
       this->setFocusPolicy(Qt::StrongFocus)
}

myGLWidget::myGLWidget() : QGLWidget()
{
       this->setFocusPolicy(Qt::StrongFocus)
}

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like this

yes it works !!!

==> but i don't know why...

**meazza** · 5th July 2011, 14:26

yes it works !!!

==> but i don't know why...

Well for the widget to be able to handle key-press event the widget has to have focus. Otherwise it is the MainWindow class which has focus and when you press your keyboard the MainWindow class will handle them and not the widget. Glad it works for you and also read what peace_comp posted and that link for more info

**21did21** · 5th July 2011, 14:27

Originally Posted by peace_comp

Hi,
The Qt::FocusPolicy property holds the way the widget accepts keyboard focus (http://doc.qt.nokia.com/latest/qwidg...cusPolicy-prop)
to enable keyboard focus, add a call to setFocusPolicy(Qt::StrongFocus) in the widget constructor :

myGLWidget::myGLWidget() : QGLWidget()
{
setFocusPolicy(Qt::StrongFocus);
}

if i understand this line is to active keyboard ?

Originally Posted by meazza

Well for the widget to be able to handle key-press event the widget has to have focus. Otherwise it is the MainWindow class which has focus and when you press your keyboard the MainWindow class will handle them and not the widget. Glad it works for you and also read what peace_comp posted and that link for more info

ok thanks a lot

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