Render QWidget within QGLWidget

[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

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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;
}

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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;
    }
}

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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);

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Cheers!

Joh