How to use QOpenGLFunctions_2_1 properly

[jshafferman]

I am trying to use raw OpenGL with Qt and I am trying to strictly use the Qt API to do so. I am using OpenGL 2.1 because that is our hardware limitation. I am able to build without any errors but the first instance of a gl* fails. The first opengl function is glGetIntergv(GL_ENUM, int*) and through the debugger I am able to see that is where I crash first. I am just curious if anyone can see what I am missing because my guess is I have to do something special to initialize these functions (which I thought initializeOpenGLFunctions() accomplished). Any help or direction would be great!!

I am subclassing with QOpenGLFunctions_2_1 like so:

class GLWidget : public QGLWidget, protected QOpenGLFunctions_2_1

class GLWidget : public QGLWidget, protected QOpenGLFunctions_2_1

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These are the relevant source file functions

GLWidget::GLWidget(QWidget *parent) :
    QGLWidget(QGLFormat(QGL::DoubleBuffer | QGL::Rgba | QGL::DepthBuffer),parent)
{
    createActions();
    createMenus();
}
 
void GLWidget::initializeGL()
{
    initializeOpenGLFunctions();
 
    pixels[0] = pixels[1] = pixels[2] = NULL;
    frameGood[0] = frameGood[1] = frameGood[2] = GL_FALSE;
 
    qDebug() << "Pixel Buffer Object Demo";
 
    QGLFunctions funcs(QGLContext::currentContext());
    bool isNonPowerTwo = funcs.hasOpenGLFeature(QGLFunctions::NPOTTextures);
 
//    // Make sure required functionality is available!
//    if (!GLEE_VERSION_2_1 && !GLEE_ARB_pixel_buffer_object)
//    {
//        qDebug() << "PBO extension is not available!";
////        fprintf(stderr, "PBO extension is not available!\n");
//        Sleep(2000);
//        exit(0);
//    }
 
    if (isNonPowerTwo)
    {
        npotTexturesAvailable = GL_TRUE;
    }
    else
    {
        qDebug() << "GL_ARB_texture_non_power_of_two extension is not available!";
        qDebug() << "Only portion of window will be used for rendering";
    }
 
    // Check for minimum resources
    GLint intVal = 0;
    glGetIntegerv(GL_MAX_TEXTURE_UNITS, &intVal);
 
    if (intVal < 3)
    {
        qDebug() << "Fewer than 3 texture units available!";
        Sleep(2000);
        exit(0);
    }
    glGetIntegerv(GL_MAX_TEXTURE_SIZE, &intVal);
    if (intVal < 1024)
    {
        qDebug() << "1024x1024 texture not supported!";
        Sleep(2000);
        exit(0);
    }
 
    qDebug() << "Controls:";
    qDebug() << "\tRight-click for menu";
    qDebug() << "\tb\tToggle motion blur";
    qDebug() << "\tp\tToggle PBO usage";
    qDebug() << "\tarrows\t+/- rotation speed";
    qDebug() << "\tq\t\tExit demo";
 
    // Colors
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f );
    glColor4f(0.0f, 0.0f, 0.0f, 1.0f );
 
    // Texture matrix is the only one we'll change
    glMatrixMode(GL_TEXTURE);
 
    // Set up textures
    SetupTextures();
}

GLWidget::GLWidget(QWidget *parent) :
    QGLWidget(QGLFormat(QGL::DoubleBuffer | QGL::Rgba | QGL::DepthBuffer),parent)
{
    createActions();
    createMenus();
}

void GLWidget::initializeGL()
{
    initializeOpenGLFunctions();

    pixels[0] = pixels[1] = pixels[2] = NULL;
    frameGood[0] = frameGood[1] = frameGood[2] = GL_FALSE;

    qDebug() << "Pixel Buffer Object Demo";

    QGLFunctions funcs(QGLContext::currentContext());
    bool isNonPowerTwo = funcs.hasOpenGLFeature(QGLFunctions::NPOTTextures);

//    // Make sure required functionality is available!
//    if (!GLEE_VERSION_2_1 && !GLEE_ARB_pixel_buffer_object)
//    {
//        qDebug() << "PBO extension is not available!";
////        fprintf(stderr, "PBO extension is not available!\n");
//        Sleep(2000);
//        exit(0);
//    }

    if (isNonPowerTwo)
    {
        npotTexturesAvailable = GL_TRUE;
    }
    else
    {
        qDebug() << "GL_ARB_texture_non_power_of_two extension is not available!";
        qDebug() << "Only portion of window will be used for rendering";
    }

    // Check for minimum resources
    GLint intVal = 0;
    glGetIntegerv(GL_MAX_TEXTURE_UNITS, &intVal);

    if (intVal < 3)
    {
        qDebug() << "Fewer than 3 texture units available!";
        Sleep(2000);
        exit(0);
    }
    glGetIntegerv(GL_MAX_TEXTURE_SIZE, &intVal);
    if (intVal < 1024)
    {
        qDebug() << "1024x1024 texture not supported!";
        Sleep(2000);
        exit(0);
    }

    qDebug() << "Controls:";
    qDebug() << "\tRight-click for menu";
    qDebug() << "\tb\tToggle motion blur";
    qDebug() << "\tp\tToggle PBO usage";
    qDebug() << "\tarrows\t+/- rotation speed";
    qDebug() << "\tq\t\tExit demo";

    // Colors
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f );
    glColor4f(0.0f, 0.0f, 0.0f, 1.0f );

    // Texture matrix is the only one we'll change
    glMatrixMode(GL_TEXTURE);

    // Set up textures
    SetupTextures();
}

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And as stated above the first call to glGetIntergv is what fails . Any ideas?

[ChrisW67]

Has initializeOpenGLFunctions() returned true or failed (false)?

[jshafferman]

I haven't had a chance to check it yet, but if it is returning false why would that happen?

[jshafferman]

So it is turning out that my initializeOpenGLFunctions() is returning false. What would cause this to happen? I have already double checked to make sure that my graphics card is capable of supporting OpenGL 2.1 so I know that it isn't hardware related. Any ideas?

[ChrisW67]

Well, the QOpenGLFunctions example sets a surface type and creates a GL context in the class constructor and makes that current before calling initializeOpenGLFunctions.

[jshafferman]

Isn't the SetSurfaceType specific to a QWindow not a QWidget? I have seen that example but I didn't think it applied to the QGLWidget.

[ChrisW67]

This is where my broken link should have been pointing http://qt-project.org/doc/qt-5.0/qtg...s.html#details

Yes it is QWindow but there could be a clue in the setup to use the inherited functions. I do not know from first hand use of it.

[jshafferman]

I investigated trying to use the QWindow version and I don't see how that can be applied to the QGLWidget. The QOpenGLContext takes a QSurfaceType (if I remember right) which I don't know if it makes sense to create a QSurfaceType inside of QGLWidget. Anyhow I don't see how I can piggy back off of that example. Do you have any ideas? According to the documentation for QGLWidget context should be set when calling the paintgl and initializeGL functions.

[ChrisW67]

OK. This code works for me (Linux 64-bit, Qt 5.2.0, nVidia proprietary drivers):

#include <QtWidgets>
#include <QtOpenGL>
#include <QOpenGLFunctions_2_1>
 
class GLWidget : public QGLWidget, protected QOpenGLFunctions_2_1
{
    Q_OBJECT
public:
    GLWidget(QWidget *parent = 0) :
        QGLWidget(QGLFormat(QGL::DoubleBuffer | QGL::Rgba | QGL::DepthBuffer),parent)
    {
    }
protected:
    void initializeGL()
    {
        bool ok = initializeOpenGLFunctions();
 
        // Check for minimum resources
        GLint intVal = 0;
        glGetIntegerv(GL_MAX_TEXTURE_UNITS, &intVal);
        qDebug() << ok << intVal;        // true, 4 on my machine
    }
};
 
int main(int argc, char **argv) {
    QApplication app(argc, argv);
    GLWidget w;
    w.show();
    return app.exec();
}
#include "main.moc"

#include <QtWidgets>
#include <QtOpenGL>
#include <QOpenGLFunctions_2_1>

class GLWidget : public QGLWidget, protected QOpenGLFunctions_2_1
{
    Q_OBJECT
public:
    GLWidget(QWidget *parent = 0) :
        QGLWidget(QGLFormat(QGL::DoubleBuffer | QGL::Rgba | QGL::DepthBuffer),parent)
    {
    }
protected:
    void initializeGL()
    {
        bool ok = initializeOpenGLFunctions();

        // Check for minimum resources
        GLint intVal = 0;
        glGetIntegerv(GL_MAX_TEXTURE_UNITS, &intVal);
        qDebug() << ok << intVal;        // true, 4 on my machine
    }
};

int main(int argc, char **argv) {
    QApplication app(argc, argv);
    GLWidget w;
    w.show();
    return app.exec();
}
#include "main.moc"

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Your initializeOpenGLFunctions() returning false would indicate that there is no OpenGL support on your system.

[jshafferman]

Well I'll be... It appears that the laptop I am using to work with 'says' it has OpenGL support for 2.1 however if I change the QOpenGLFunction_2_1 to 2_0 or 1_* it appears to start working! So I am glad to learn that if initializeOpenGLFunctions fails it is because that particular version of OpenGL is not supported on your system. I wish the Qt doucmentation just said that , however thank you very much for your help! I am sure I will have more questions about Qt and OpenGL as get more involved with the process. Thanks!

[ChrisW67]

It is not ideal documentation, but see the second last paragraph in the detailed description of QAbstractOpenGLFunctions.