Render QWidget within QGLWidget

[crazymonkey]

Hello All This is my first post on this forum. but i have a question (i dont know if it is a newbie question or not)

I have been using/learning Qt over the past week or so, I'm comfortable with Qt and OpenGL to the point where i know how to use standard OpenGL API commands within Qt.

Firstly I have done some searching and found http://doc.trolltech.com/qq/qq26-openglcanvas.html which is exactly what im trying to achieve, but when i try to compile and run the example code it doesn't work. these widgets also need to have their own event listeners etc...

does anybody know if this is the only way to do this? any help will be appreciated.

Thanks

Crazymonkey

[JohannesMunk]

Hi!

What doesn't work? Describe the problem! What event listeners?

Joh

[crazymonkey]

This qWarning pops up several times when i run the program.

if (painter->paintEngine()->type() != QPaintEngine::OpenGL) {
        qWarning("OpenGLScene: drawBackground needs a QGLWidget to be set as viewport on the graphics view");
        return;
    }

if (painter->paintEngine()->type() != QPaintEngine::OpenGL) {
        qWarning("OpenGLScene: drawBackground needs a QGLWidget to be set as viewport on the graphics view");
        return;
    }

To copy to clipboard, switch view to plain text mode 

JohannesMunk what I meant to say is that these Widgets which are embedded within my QGLWidget Scene must be able to handle their own event listeners as well


PS im running Qt 4.7.0 with Qt Creator 2.0

[JohannesMunk]

Well the warning says that your viewport setup didn't work.
Did you copy/leave this line in place?

view.setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));

view.setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));

To copy to clipboard, switch view to plain text mode 

Yes for sure if you want the widgets to work in a certain way, you will have to code their eventhandlers.

What do you want to do? Where is the problem?

Joh

[crazymonkey]

Joh i never altered the above code in any way. it's just giving me those errors (those qWarnings)

What could the problem be? is it my PC?

I ultimately want to embed a normal QWidget within a QGLWidget. at the moment all i have is a QGLWidget which renders my scene. now i want to add those widgets ontop so i can get user input/output.

[JohannesMunk]

Ok. Step by step. You need to setup a QGraphicsView/Scene properly.

main.cpp:
 
#include <QtCore>
#include <QtGui>
 
#include "main.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
 
    MainWindow w;
    w.show();
    return a.exec();
}
 
---------------------------
main.h:
 
#ifndef MAIN_H
#define MAIN_H
 
#include <QtCore>
#include <QtGui>
#include <QtOpenGL>
 
using namespace std;
 
class MainWindow : public QMainWindow
{
public:
    MainWindow(QWidget *parent = 0);
private:
    QGraphicsScene *scene;
    QGraphicsView *graphicsView;
};
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent)
{
    scene = new QGraphicsScene();
 
    QPushButton* btn = new QPushButton("Test");
    scene->addWidget(btn);
 
    graphicsView = new QGraphicsView(this);
    graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
    graphicsView->setScene(scene);
    graphicsView->setGeometry(QRect(50, 50, 500, 300));
    graphicsView->show();
 
    this->setCentralWidget(graphicsView);
 
}
 
#endif // MAIN_H

main.cpp:

#include <QtCore>
#include <QtGui>

#include "main.h"

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

    MainWindow w;
    w.show();
    return a.exec();
}

---------------------------
main.h:

#ifndef MAIN_H
#define MAIN_H

#include <QtCore>
#include <QtGui>
#include <QtOpenGL>

using namespace std;

class MainWindow : public QMainWindow
{
public:
    MainWindow(QWidget *parent = 0);
private:
    QGraphicsScene *scene;
    QGraphicsView *graphicsView;
};

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent)
{
    scene = new QGraphicsScene();

    QPushButton* btn = new QPushButton("Test");
    scene->addWidget(btn);

    graphicsView = new QGraphicsView(this);
    graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
    graphicsView->setScene(scene);
    graphicsView->setGeometry(QRect(50, 50, 500, 300));
    graphicsView->show();

    this->setCentralWidget(graphicsView);

}

#endif // MAIN_H

To copy to clipboard, switch view to plain text mode 

Don't forget to add

QT += opengl

to your pro file.

Does that work?

Joh

[JohannesMunk]

Now we render the background of the scene with our own OpenGL calls..

#ifndef MAIN_H
#define MAIN_H
 
#include <QtCore>
#include <QtGui>
#include <QtOpenGL>
 
using namespace std;
 
class OpenGLScene : public QGraphicsScene
{
public:
    OpenGLScene() {
 
    }
protected:
    void drawBackground(QPainter *painter, const QRectF &);
};
 
void OpenGLScene::drawBackground(QPainter *painter, const QRectF &)
{
    /*if (painter->paintEngine()->type() != QPaintEngine::OpenGL) {
        qWarning("OpenGLScene: drawBackground needs a "
                 "QGLWidget to be set as viewport on the "
                 "graphics view");
        return;
    }*/
    //
    QColor m_backgroundColor = QColor("yellow");
    glClearColor(m_backgroundColor.redF(),
                 m_backgroundColor.greenF(),
                 m_backgroundColor.blueF(), 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
}
 
 
class MainWindow : public QMainWindow
{
public:
    MainWindow(QWidget *parent = 0);
private:
    OpenGLScene *scene;
    QGraphicsView *graphicsView;
};
 
 
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent)
{
    scene = new OpenGLScene();
 
    QPushButton* btn = new QPushButton("Test");
    scene->addWidget(btn);
 
    graphicsView = new QGraphicsView(this);
    graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
    graphicsView->setScene(scene);
    graphicsView->setGeometry(QRect(50, 50, 500, 300));
    graphicsView->show();
 
    this->setCentralWidget(graphicsView);
 
}
 
#endif // MAIN_H

#ifndef MAIN_H
#define MAIN_H

#include <QtCore>
#include <QtGui>
#include <QtOpenGL>

using namespace std;

class OpenGLScene : public QGraphicsScene
{
public:
    OpenGLScene() {

    }
protected:
    void drawBackground(QPainter *painter, const QRectF &);
};

void OpenGLScene::drawBackground(QPainter *painter, const QRectF &)
{
    /*if (painter->paintEngine()->type() != QPaintEngine::OpenGL) {
        qWarning("OpenGLScene: drawBackground needs a "
                 "QGLWidget to be set as viewport on the "
                 "graphics view");
        return;
    }*/
    //
    QColor m_backgroundColor = QColor("yellow");
    glClearColor(m_backgroundColor.redF(),
                 m_backgroundColor.greenF(),
                 m_backgroundColor.blueF(), 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
}


class MainWindow : public QMainWindow
{
public:
    MainWindow(QWidget *parent = 0);
private:
    OpenGLScene *scene;
    QGraphicsView *graphicsView;
};



MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent)
{
    scene = new OpenGLScene();

    QPushButton* btn = new QPushButton("Test");
    scene->addWidget(btn);

    graphicsView = new QGraphicsView(this);
    graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
    graphicsView->setScene(scene);
    graphicsView->setGeometry(QRect(50, 50, 500, 300));
    graphicsView->show();

    this->setCentralWidget(graphicsView);

}

#endif // MAIN_H

To copy to clipboard, switch view to plain text mode 

Aah! Something is wrong with this check! Did produce the same warning here. But the OpenGL stuff obviously works!

Joh

[JohannesMunk]

That check should be nowadays:

if ((painter->paintEngine()->type() != QPaintEngine::OpenGL2) &&
    (painter->paintEngine()->type() != QPaintEngine::OpenGL))
{
    qWarning("OpenGLScene: drawBackground needs a "
             "QGLWidget to be set as viewport on the "
             "graphics view");
    return;
}

if ((painter->paintEngine()->type() != QPaintEngine::OpenGL2) &&
    (painter->paintEngine()->type() != QPaintEngine::OpenGL))
{
    qWarning("OpenGLScene: drawBackground needs a "
             "QGLWidget to be set as viewport on the "
             "graphics view");
    return;
}

To copy to clipboard, switch view to plain text mode 

HIH

Joh

[crazymonkey]

Thanks Joh ill try the above mentioned when i get back from work

speaking of which, i tried to run the qq26-openglcanvas program on an Ubuntu 10.04 PC with Qt 4.6.2 and this code runs fine. howcome?

BTW my home PC is Windows 7 using Qt 4.7.0

[JohannesMunk]

I guess your Ubuntu only supports/has drivers for OpenGL 1.0.
Happy coding

[crazymonkey]

Thanks Joh, youve helped alot!

quick question: where do i make my usual updateGL() , resizeGL() and paintGL() calls then?

[JohannesMunk]

You don't!

paintGL => drawBackground
or if you want individual items, subclass QGraphicsItem implement boundingRect and paintEvent (using either QPainter stuff or native OpenGL calls with QPainter.beginNativePainting() .. )

http://www.qtcentre.org/threads/34148-Qt-and-OpenGl-(I-m-lost)?p=158675#post158675

resizeGL => taken care of the view, otherwise subclass QGraphicsView, implement resizeEvent.
updateGL => not necessary.

Joh

[crazymonkey]

and if i want to use listeners to zoom in/out of my openGL scene is it done in the same way as i would normally do it?

[JohannesMunk]

Yes. You can then update the view either manually (view->update()), when something changes - or periodically with a Timer (fixed framerate), depends.

Or you split your scene and implement different QGraphicsItems. Call their update() function to trigger a redraw of them.

Joh

[crazymonkey]

Sorry and what about initializeGL() ??

im very noob sorry for all these questions!

[JohannesMunk]

InitializeGL. Bit tricky that one.

Your example http://doc.trolltech.com/qq/qq26-openglcanvas.html doesn't use any opengl initialization. Does it on every repaint.

drawBackground is called every 20ms due to (view.setViewportUpdateMode(QGraphicsView::FullVie wportUpdate); in main.cpp and QTimer::singleShot(20, this, SLOT(update())); at the end of drawBackground)

If that's too expensive for you, because you need to setup big displaylists or something like that, you could:

1) Do one of these: http://stackoverflow.com/questions/1...stom-qglwidget

2) Have a look at the boxes demo: http://doc.trolltech.com/latest/demos-boxes.html

3) "Dirty", but efficient Hack:

class OpenGLScene : ..
{
private:
    bool initialized;
}
 
OpenGLScene::OpenGLScene(..)
{
    initialized = false;
}
 
void OpenGLScene::drawBackground(QPainter *painter, const QRectF &)
{
    if (initialized == false)
    {
         // your initialization goes here..
         initialized = true;
    }
}

class OpenGLScene : ..
{
private:
    bool initialized;
}

OpenGLScene::OpenGLScene(..)
{
    initialized = false;
}

void OpenGLScene::drawBackground(QPainter *painter, const QRectF &)
{
    if (initialized == false)
    {
         // your initialization goes here..
         initialized = true;
    }
}

To copy to clipboard, switch view to plain text mode 

Joh

[crazymonkey]

hello Joh im having difficulty in adding new widgets

i think this is more of a Qt specific question but what command can i use to set the position of my widgets on my scene?

i have added widgets made via Qt designer perfectly fine. but now i want to make them movable with mouse dragging.

also my widget doesn't have a title like in the example shown http://doc.trolltech.com/qq/qq26-openglcanvas.html

how do i make them movable via mouse dragging and how do i show a title (eg "Instructions")

[JohannesMunk]

Hi!

You could have looked it up in the example you referred to!

QWidget* w = new QWidget();
w->setGeometry(0,0,150,150);
w->setWindowTitle("Title");
QGraphicsProxyWidget* proxy = scene->addWidget(w);
proxy->setWindowFlags(Qt::Dialog | Qt::CustomizeWindowHint | Qt::WindowTitleHint);
proxy->setPos(10,10);

QWidget* w = new QWidget();
w->setGeometry(0,0,150,150);
w->setWindowTitle("Title");
QGraphicsProxyWidget* proxy = scene->addWidget(w);
proxy->setWindowFlags(Qt::Dialog | Qt::CustomizeWindowHint | Qt::WindowTitleHint);
proxy->setPos(10,10);

To copy to clipboard, switch view to plain text mode 

Cheers!

Joh

[crazymonkey]

sorry i meant how do make it draggable across the scene?

[JohannesMunk]

you can take it and drag it around this way. what else do you want?