Question

currently i am trying to laod *.obj-files into my programm. My code is based on this example:

Accelerate your widgets with OpenGL(changed link)

The only differeence in my code, is that i have a glwidget-class, in which all the drawing is defined. In the class OpenGLScene only my Gui is defined. In the function drawBackground(QPainter *painter, const QRectF &) i call the function paintGL.

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

painter->beginNativePainting();

glClearColor(m_backgroundColor.redF(), m_backgroundColor.greenF(), m_backgroundColor.blueF(), 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

if (m_model) {

    m_model->paintGL();
}

painter->endNativePainting();

}

Simple drawing and stuff works fine. I only get problems until i try to load *.obj-Files. I have tried several things, which didnt work.
Now I ended up with the solution to define all the functions from the model-class(which you can find in the example) in my glWidget-Class and then calling the render-function in paintGL. Afterwards calling the paintGL in OpenGLScene.

Here you can see my header-files: OpenGLScene.h and GLWidget.h:

class GLWidget : public QGLWidget
{
Q_OBJECT
public:
float           m_distance;
GLWidget(const QString &filePath);
GLWidget(QWidget *parent = 0);
~GLWidget();
QSize           minimumSizeHint() const;
QSize           sizeHint() const;
void            initializeGL();
void            paintGL();
void            resizeGL(int width, int height);
void render() const;
QString fileName() const { return m_fileName; }
int faces() const { return m_pointIndices.size() / 3; }
int edges() const { return m_edgeIndices.size() / 2; }
int points() const { return m_points.size(); }
QString m_fileName;
QVector<Point3d> m_points;
QVector<Point3d> m_normals;
QVector<int> m_edgeIndices;
QVector<int> m_pointIndices;
};


#ifndef QT_NO_CONCURRENT
#include <QFutureWatcher>
#endif

class GLWidget;

class OpenGLScene : public QGraphicsScene
{
Q_OBJECT

public:
OpenGLScene();
void drawBackground(QPainter *painter, const QRectF &rect);
QDialog *createDialog(const QString &windowTitle) const;

void setModel(GLWidget *model);

//Model       *m_model;
GLWidget    *m_model;
QColor      m_backgroundColor;
float       m_distance;
QLabel      *m_labels[4];
QWidget     *m_modelButton;
#ifndef QT_NO_CONCURRENT
QFutureWatcher<GLWidget *> m_modelLoader;
#endif
public slots:
void loadModel();
void loadModel(const QString &filePath);
void modelLoaded();
};

Unfortunately this idea isnt working, because i get this error:

“It is not safe to use pixmaps outside the GUI thread”

But I really dont understand whats that supposed to mean.

Answer 1

If you’ve moved all the Model stuff into GLWidget then I assume you are now creating your GLWidget instance in ::loadModel? If so then be aware that this is being created in a new thread. It looks like it doesn’t automatically get moved into the main (GUI) thread when the loading thread finishes. What actually happens to the QObject is an open question.

If you want to disable threading completely in order to simplify things then remove the lines

#ifndef QT_NO_CONCURRENT
#include <QFutureWatcher>
#endif

and

#ifndef QT_NO_CONCURRENT
QFutureWatcher<Model *> m_modelLoader;
#endif

in openglscene.h. In the OpenGLScene constructor body remove the lines

#ifndef QT_NO_CONCURRENT
    connect(&m_modelLoader, SIGNAL(finished()), this, SLOT(modelLoaded()));
#endif

In OpenGLScene::loadModel(const QString &filePath) change

#ifndef QT_NO_CONCURRENT
    m_modelLoader.setFuture(QtConcurrent::run(::loadModel, filePath));
#else
    setModel(::loadModel(filePath));
    modelLoaded();
#endif

to just

    setModel(::loadModel(filePath));
    modelLoaded();

Finally remove

#ifndef QT_NO_CONCURRENT
    setModel(m_modelLoader.result());
#endif

from OpenGLScene::modelLoaded().