QGraphicsView, OpenGL, Buffer Objects

[klou]

QGraphicsItem has a code to render itself using OpenGL. When I use Buffer Objects and add simple QGraphicsItem program simetimes crashes, sometimes not.
main.h:

#include <QtGui/QApplication>
#include "myQGraphicsView.h"
 
int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	myQGraphicsView w;
	w.show();
	return a.exec();
}

#include <QtGui/QApplication>
#include "myQGraphicsView.h"

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
	myQGraphicsView w;
	w.show();
	return a.exec();
}

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myQGraphicsView:

#ifndef MYQGRAPHICSVIEW_H_
#define MYQGRAPHICSVIEW_H_
 
#include <QGLWidget>
#include <QGraphicsView>
#include <QResizeEvent>
 
class itemWrap;
class myQGraphicsView: public QGraphicsView
{
	friend itemWrap;
public:
	myQGraphicsView(QWidget *parent = 0);
	~myQGraphicsView();
 
private:
	void updateMap();
 
	GLuint vbo;
};
#endif

#ifndef MYQGRAPHICSVIEW_H_
#define MYQGRAPHICSVIEW_H_

#include <QGLWidget>
#include <QGraphicsView>
#include <QResizeEvent>

class itemWrap;
class myQGraphicsView: public QGraphicsView
{
	friend itemWrap;
public:
	myQGraphicsView(QWidget *parent = 0);
	~myQGraphicsView();

private:
	void updateMap();

	GLuint vbo;
};
#endif

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myQGraphicsView.cpp:

#include "myQGraphicsView.h"
#include <QGraphicsRectItem>
#include <QPointer>
 
#include <gl/GL.h>
#include <gl/glext.h>
 
PFNGLGENBUFFERSPROC glGenBuffers = 0;
PFNGLBINDBUFFERPROC glBindBuffer = 0;
PFNGLBUFFERDATAPROC glBufferData = 0;
PFNGLDELETEBUFFERSPROC glDeleteBuffers = 0;
 
GLfloat vboVerticies2[4 * 3] =
							{
								-1.0, -1.0, 0.0,
								0.0, -1.0, 0.0,
								-1.0,  0.0, 0.0,
								0.0,  0.0, 0.0	
							};
 
class itemWrap: public QGraphicsRectItem
{
	QPointer<myQGraphicsView> view_;
public:
	itemWrap(myQGraphicsView * obj){view_ = obj;}
	~itemWrap(){};
	void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget /* = 0 */) 
	{
		GLint proj[16];
		GLfloat model[16];
		glMatrixMode(GL_PROJECTION);
		glLoadIdentity();
		glMatrixMode(GL_MODELVIEW);
		glLoadIdentity();
		glGetIntegerv(GL_PROJECTION_MATRIX,proj);
		glGetFloatv(GL_MODELVIEW_MATRIX,model);
 
		if(!view_.isNull())
		{
			painter->beginNativePainting();
			view_->updateMap();
			painter->endNativePainting();
		}
	}
};
 
 
myQGraphicsView::myQGraphicsView( QWidget *parent /*= 0*/ )
:QGraphicsView(parent)
{
	setViewport(new QGLWidget);
	setScene(new QGraphicsScene(QRect(0,0,100,100), this));
	QGraphicsRectItem * ri = new itemWrap(this);
	ri->setRect(0,0, 100, 100);
	ri->setBrush(QBrush(QColor(0,0,0,0)));
	scene()->addItem(ri);
 
	ri = new QGraphicsRectItem();
	ri->setRect(50, 50, 100, 100);
	ri->setBrush(QBrush(QColor(Qt::red)));
	ri->setZValue(10);
	scene()->addItem(ri);
 
}
 
myQGraphicsView::~myQGraphicsView()
{
glDeleteBuffers(1,&vbo);
}
 
void myQGraphicsView::updateMap()
{
	if (!glGenBuffers)
	{
		glGenBuffers = (PFNGLGENBUFFERSPROC)wglGetProcAddress("glGenBuffers");
		glBindBuffer = (PFNGLBINDBUFFERPROC)wglGetProcAddress("glBindBuffer");
		glBufferData = (PFNGLBUFFERDATAPROC)wglGetProcAddress("glBufferData");
		glDeleteBuffers = (PFNGLDELETEBUFFERSPROC)wglGetProcAddress("glDeleteBuffers");
 
		glEnableClientState(GL_VERTEX_ARRAY);
		glVertexPointer(3,GL_FLOAT,0,0);
		glGenBuffers(1,&vbo);
		glBindBuffer(GL_ARRAY_BUFFER,vbo);
		//glBufferData(GL_ARRAY_BUFFER,12*sizeof(GLfloat),vboVerticies2,GL_STATIC_DRAW);
		glVertexPointer(3,GL_FLOAT,0,0);
	}
 
	GLuint glErr = glGetError();
	char* gluErrStr = (char*)gluErrorString(glErr);	
 
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
 
	/*glColor3f(1.0,0.5,0.0);
	glBindBuffer(GL_ARRAY_BUFFER,vbo);
	glVertexPointer(3,GL_FLOAT,0,0);
	glDrawArrays(GL_TRIANGLE_STRIP,0,4);*/
 
	glBegin(GL_TRIANGLES);
		glVertex3f( 0.1,-0.1,0.0);
		glVertex3f( 0.5, 0.2,0.0);
		glVertex3f( 0.4, 1.0,0.0);
	glEnd();
}

#include "myQGraphicsView.h"
#include <QGraphicsRectItem>
#include <QPointer>

#include <gl/GL.h>
#include <gl/glext.h>

PFNGLGENBUFFERSPROC glGenBuffers = 0;
PFNGLBINDBUFFERPROC glBindBuffer = 0;
PFNGLBUFFERDATAPROC glBufferData = 0;
PFNGLDELETEBUFFERSPROC glDeleteBuffers = 0;

GLfloat vboVerticies2[4 * 3] =
							{
								-1.0, -1.0, 0.0,
								0.0, -1.0, 0.0,
								-1.0,  0.0, 0.0,
								0.0,  0.0, 0.0	
							};

class itemWrap: public QGraphicsRectItem
{
	QPointer<myQGraphicsView> view_;
public:
	itemWrap(myQGraphicsView * obj){view_ = obj;}
	~itemWrap(){};
	void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget /* = 0 */) 
	{
		GLint proj[16];
		GLfloat model[16];
		glMatrixMode(GL_PROJECTION);
		glLoadIdentity();
		glMatrixMode(GL_MODELVIEW);
		glLoadIdentity();
		glGetIntegerv(GL_PROJECTION_MATRIX,proj);
		glGetFloatv(GL_MODELVIEW_MATRIX,model);

		if(!view_.isNull())
		{
			painter->beginNativePainting();
			view_->updateMap();
			painter->endNativePainting();
		}
	}
};


myQGraphicsView::myQGraphicsView( QWidget *parent /*= 0*/ )
:QGraphicsView(parent)
{
	setViewport(new QGLWidget);
	setScene(new QGraphicsScene(QRect(0,0,100,100), this));
	QGraphicsRectItem * ri = new itemWrap(this);
	ri->setRect(0,0, 100, 100);
	ri->setBrush(QBrush(QColor(0,0,0,0)));
	scene()->addItem(ri);

	ri = new QGraphicsRectItem();
	ri->setRect(50, 50, 100, 100);
	ri->setBrush(QBrush(QColor(Qt::red)));
	ri->setZValue(10);
	scene()->addItem(ri);

}

myQGraphicsView::~myQGraphicsView()
{
glDeleteBuffers(1,&vbo);
}

void myQGraphicsView::updateMap()
{
	if (!glGenBuffers)
	{
		glGenBuffers = (PFNGLGENBUFFERSPROC)wglGetProcAddress("glGenBuffers");
		glBindBuffer = (PFNGLBINDBUFFERPROC)wglGetProcAddress("glBindBuffer");
		glBufferData = (PFNGLBUFFERDATAPROC)wglGetProcAddress("glBufferData");
		glDeleteBuffers = (PFNGLDELETEBUFFERSPROC)wglGetProcAddress("glDeleteBuffers");

		glEnableClientState(GL_VERTEX_ARRAY);
		glVertexPointer(3,GL_FLOAT,0,0);
		glGenBuffers(1,&vbo);
		glBindBuffer(GL_ARRAY_BUFFER,vbo);
		//glBufferData(GL_ARRAY_BUFFER,12*sizeof(GLfloat),vboVerticies2,GL_STATIC_DRAW);
		glVertexPointer(3,GL_FLOAT,0,0);
	}

	GLuint glErr = glGetError();
	char* gluErrStr = (char*)gluErrorString(glErr);	

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();

	/*glColor3f(1.0,0.5,0.0);
	glBindBuffer(GL_ARRAY_BUFFER,vbo);
	glVertexPointer(3,GL_FLOAT,0,0);
	glDrawArrays(GL_TRIANGLE_STRIP,0,4);*/

	glBegin(GL_TRIANGLES);
		glVertex3f( 0.1,-0.1,0.0);
		glVertex3f( 0.5, 0.2,0.0);
		glVertex3f( 0.4, 1.0,0.0);
	glEnd();
}

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If I uncomment lines in myQGraphicsView.cpp:

glBufferData(GL_ARRAY_BUFFER,12*sizeof(GLfloat),vboVerticies2,GL_STATIC_DRAW);
....
glColor3f(1.0,0.5,0.0);
glBindBuffer(GL_ARRAY_BUFFER,vbo);
glVertexPointer(3,GL_FLOAT,0,0);
glDrawArrays(GL_TRIANGLE_STRIP,0,4);

glBufferData(GL_ARRAY_BUFFER,12*sizeof(GLfloat),vboVerticies2,GL_STATIC_DRAW);
....
glColor3f(1.0,0.5,0.0);
glBindBuffer(GL_ARRAY_BUFFER,vbo);
glVertexPointer(3,GL_FLOAT,0,0);
glDrawArrays(GL_TRIANGLE_STRIP,0,4);

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almost everytime program crashes.
Is it bug or I made something wrong?

p.s. sources in attachment too

---

Added after 4 minutes:

Under Debugger it crashes in qpaintengineex_opengl2.cpp:

void QGL2PaintEngineExPrivate::composite(const QGLRect& boundingRect)
{
    setCoords(staticVertexCoordinateArray, boundingRect);
    setVertexAttributePointer(QT_VERTEX_COORDS_ATTR, staticVertexCoordinateArray);
    glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
}

void QGL2PaintEngineExPrivate::composite(const QGLRect& boundingRect)
{
    setCoords(staticVertexCoordinateArray, boundingRect);
    setVertexAttributePointer(QT_VERTEX_COORDS_ATTR, staticVertexCoordinateArray);
    glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
}

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on line

glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

glDrawArrays(GL_TRIANGLE_FAN, 0, 4);

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