c++ - What is the proper order of initialization of OpenGL inside a QT GraphicsScene? -

the following qt sample straightforward : i'm trying find out why texture shows if application gets timed messagebox. i'm using qt4.8.1 , tried both under linux , vs2008.

#include "ui_qtgltest.h" #include <qtgui/qapplication> #include <qtgui/qmainwindow> #include <qgraphicspixmapitem> #include <qgraphicsscene> #include <qglwidget> #include <qmessagebox> #include <qdebug> #include <qtimer>  class glitem : public qgraphicspixmapitem  // item issue opengl commands {     gluint texture[1] ;     glsizei w, h; public:      glitem(qgraphicsitem *parent = null) : qgraphicspixmapitem(parent){             // when following line commented out, texture doesn't show up.         qmessagebox::warning(null,qstring("???"),qstring("hold on second") );          qimage img( "im0.png" ) ;         qimage gl_formatted_image;         gl_formatted_image = qglwidget::converttoglformat(img);         w = gl_formatted_image.width();         h = gl_formatted_image.height();          glgentextures(1, texture);         glbindtexture(gl_texture_2d, texture[0]);                    glteximage2d( gl_texture_2d, 0, gl_rgba,             gl_formatted_image.width(), gl_formatted_image.height(),             0, gl_rgba, gl_unsigned_byte, gl_formatted_image.bits() );           gltexparameteri(gl_texture_2d, gl_texture_wrap_s, gl_repeat);         gltexparameteri(gl_texture_2d, gl_texture_wrap_t, gl_repeat);         gltexparameteri( gl_texture_2d, gl_texture_min_filter, gl_linear );         gltexparameteri( gl_texture_2d, gl_texture_mag_filter, gl_linear );          gltexenvf(gl_texture_env, gl_texture_env_mode, gl_modulate);         glbindtexture(gl_texture_2d, 0);      }      ~glitem(void){}      void paint(qpainter *paint, const qstyleoptiongraphicsitem *option, qwidget *widget)     {         paint->setrenderhint(qpainter::antialiasing);         paint->beginnativepainting();          glclearcolor( 0.5f, 0.5f, 0.5f, 0.0f);         glclear( gl_color_buffer_bit );          glmatrixmode( gl_modelview );         glloadidentity();         glenable    ( gl_blend ) ;         glblendfunc(gl_src_alpha, gl_one_minus_src_alpha);          glenable(gl_texture_2d);         glbindtexture(gl_texture_2d, texture[0]);          glbegin(gl_quads);         gltexcoord2i( 1, 0 );    glcolor3f(1,0,0); glvertex2f( w,    0.0f);         gltexcoord2i( 1, 1 );    glcolor3f(0,1,0); glvertex2f( w,    h);         gltexcoord2i( 0, 1 );    glcolor3f(0,0,1); glvertex2f( 0.0f, h);         gltexcoord2i( 0, 0 );    glcolor3f(1,0,1); glvertex2f( 0.0f, 0.0f);         glend();          paint->endnativepainting();     } };  class qtgl: public qmainwindow { public:      qtgl(qwidget *parent =0, qt::wflags flags=0) : qmainwindow(parent, flags)     {         ui.setupui(this);     }      void setup()      {                    qglwidget   * glw   = new qglwidget(qglformat(qgl::samplebuffers));          qgraphicsscene  * s = new qgraphicsscene();         qgraphicsview   * g =  ui.graphicsview;         g->setviewport(glw);          g->setscene(s);          glitem * gi = new glitem();         s->additem( gi );            qtimer  * timer = new qtimer(this);         connect(timer, signal(timeout()), s, slot(update()));         timer->start(10);      }         ~qtgl() {}  private:     ui::mainwindow ui; };  int main(int argc, char *argv[]) {     qapplication a(argc, argv);     qtgl w;     w.show();     w.setup();     return a.exec(); } 

any idea on how debug , figure out going on inside ?