Opengl3.x and Qt under Linux

[imported_icepic1984]

Hi!

I currently try too create a Opengl3.x compatible QWidget under Linux. I use some source from this post:

http://www.opengl.org/discussion_boards
/ubbthreads.php?ubb=showflat&Number=262519

The context opens without an error, but the window is not created on my MainWindow. Instead there is a new window next to my gui. Any idea how i can embed the context on my gui-window? Have anybody a working example?

Code looks like that:

main.cpp:

 int main(int argc, char *argv[])
      {
          QApplication app(argc, argv);
     
          MainWindow mainwindow;
          mainwindow.show();
          return app.exec();
 }

mainwindow.cpp

MainWindow::MainWindow(QWidget *parent)
         : QMainWindow(parent)
     {
         ui.setupUi(this);
         connect(ui.mButtonTest,SIGNAL(clicked()),this,SLOT(printHello()));
 }

The newly created QWidget with the gl3-context is set on the mainwindow with the qtdesigner and looks like that

GL3Widget::GL3Widget(QWidget *parent):
             QWidget(parent)
     {   
         
         
         initWindow();
     
     }    

Init Framebuffer:

 void GL3Widget::initWindow()
     {
         setAttribute(Qt::WA_PaintOnScreen);
         setAttribute(Qt::WA_NoSystemBackground);
         setAutoFillBackground(true);
     
         static int visual_attribs[] = {
             GLX_X_RENDERABLE    , True,
             GLX_DRAWABLE_TYPE   , GLX_WINDOW_BIT,
             GLX_RENDER_TYPE     , GLX_RGBA_BIT,
             GLX_X_VISUAL_TYPE   , GLX_TRUE_COLOR,
             GLX_RED_SIZE        , 8,
             GLX_GREEN_SIZE      , 8,
             GLX_BLUE_SIZE       , 8,
             GLX_ALPHA_SIZE      , 8,
             GLX_DEPTH_SIZE      , 24,
             GLX_STENCIL_SIZE    , 8,
             GLX_DOUBLEBUFFER    , True,
             //GLX_SAMPLE_BUFFERS  , 1,
             //GLX_SAMPLES         , 4,
             None
         };
     
         const QX11Info &xinfo = x11Info();
         Display *display = xinfo.display();
     
         XVisualInfo *vi = NULL;
         Window window = 0;
         int fbcount = 0;
     
         GLXFBConfig *fbc = glXChooseFBConfig( display, DefaultScreen( display ),
                                               visual_attribs, &fbcount );
         if ( !fbc ) {
             printf( "Failed to retrieve a framebuffer config
" );
             exit(1);
         }
     
         mFBConfig = fbc[0];
         XFree(fbc);
     
         printf( "Found %d matching FB configs.
", fbcount );
     
     
         vi = glXGetVisualFromFBConfig( display, mFBConfig );
         XSetWindowAttributes swa;
         swa.colormap = XCreateColormap( display, RootWindow( display, vi->screen )
 swa.background_pixmap = None ;
         swa.border_pixel      = 0;
         swa.event_mask        = StructureNotifyMask;
     
     
         printf( "Creating window
" );
         Window win = XCreateWindow( display, RootWindow( display, vi->screen ),
                                     0, 0, 100, 100, 0, vi->depth, InputOutput,
                                     vi->visual,
                                     CWBorderPixel | CWColormap | CWEventMask, &swa );
         if ( !win ) {
             printf( "Failed to create window.
" );
             exit(1);
         }
     
         std::cout << "QT" << std::endl;
         create(win, true, true);
     
         mGL3Context = 0;
         initContext();
     }

Create context:

void GL3Widget::initContext()
     {
         Display *display;
         {
             const QX11Info &xinfo = x11Info();
             display = xinfo.display();
         }
     
         XVisualInfo *vi = glXGetVisualFromFBConfig(display, mFBConfig);
         GLXContext tempContext = glXCreateContext(display, vi, 0, True);
     
         glXCreateContextAttribsARBProc glXCreateContextAttribsARB = 0;
         glXCreateContextAttribsARB = (glXCreateContextAttribsARBProc)
                                      glXGetProcAddress( (const GLubyte *) "glXCreateContextAttribsARB" );
     
         glXMakeCurrent(display, 0, 0);
         glXDestroyContext(display, tempContext);
     
         int attribs[] = {
             GLX_CONTEXT_MAJOR_VERSION_ARB, 3/*requestedGLVersion.Major*/,
             GLX_CONTEXT_MINOR_VERSION_ARB, 0/*requestedGLVersion.Minor*/,
             None
         };
     
         mGL3Context = glXCreateContextAttribsARB(display, mFBConfig, 0, True, attribs);
         if (mGL3Context == NULL) {
             std::cout << "Context failed" << std::endl;
             exit(1);
         }
     
         if (glXIsDirect(display, mGL3Context) != True) {
             std::cout << "The gl context is not direct." << std::endl;
             exit(1);
         }
     
     }
     
     

Thx for help!

[Rosario_Leonardi]

If you don’t need the menu just do that:

int main(int argc, char *argv[])
{
   QApplication app(argc, argv);
     
   GL3Widget mainwindow;
   mainwindow.show();
   return app.exec();
 }

When you create a widget without a parent it become an indipendent window

Otherwise you can do

MainWindow::MainWindow(QWidget *parent)
         : QMainWindow(parent), glContext(parent)
{
         ui.setupUi(this);
connect(ui.mButtonTest,SIGNAL(clicked()),this,SLOT(printHello()));
}

[imported_icepic1984]

I know, but the problem is, when i choose your last method, 2 independent windows are created. But context-widget should placed on my MainWindow.

[Rosario_Leonardi]

ehm… sorry, I didn’t tested the second solution, I always use the first.

I imagine your MainWindow should have a private attribute like this

protected:
   GL3Widget glWig_;

As I told you before you need to pass a correct parent to your widget.

MainWindow::MainWindow(QWidget *parent)
         : QMainWindow(parent), glWig_(this)
{
   ui.setupUi(this);
   connect(ui.mButtonTest,SIGNAL(clicked()),this,SLOT(printHello()));
}

note the this pointer. In this case you have to manually resize the context every time the windows is resized.

Another (better solution) is to define a pointer to your widget and in the windows constructor call setCentralWidget like this.

MainWindow::MainWindow(QWidget *parent)
         : QMainWindow(parent)
{
   glWig_ = new Gl3Widget();
   this->setCentralWidget(glWig_);
   //....
 }

You can also use layout controller to use your openGL widget with other type of widget. Check the Qt example.

BTW: Did you try to redefine only the QGLContext class and use QGLWidget? I tried but I can’t get the windows pointer and the frame buffer descriptor… are both private.

[imported_icepic1984]

Ok i will test it. But as far as i understand the header files generated by the QtDesigner, your last method is automatically generated. I created the gui with the designer and placed my GL3Widget on it.

BTW: Did you try to redefine only the QGLContext class and use QGLWidget? I tried but I can’t get the windows pointer and the frame buffer descriptor… are both private.

I created the context on my own in a QWidget-Class. I still wonder, why there is no working solution for this problem around the inet. Nobody working with opengl 3.x and Qt here?

[Rosario_Leonardi]

I’m reading now the documentation of the new QT4.7 and it have openGl 3.2 support. Qt 4.6 support “only” ogl 3.0

http://doc.qt.nokia.com/4.7-snapshot/qglformat.html#OpenGLVersionFlag-enum

Also add the QGlBuffer to wrap VBO.

QTDesigner can create only standard widget, and is excellent to create dialog. To create custom object I prefer to write the code.