void QMyGraphicsView::drawBackground( QPainter * painter, const QRectF & rect )
{
 /* этот код рисует */
 glColor3f(0.6,0.4,0.0);
 glBegin(GL_TRIANGLES);
  glVertex2f(-0.5, -0.5);
  glVertex2f( 0.5, -0.5);
  glVertex2f( 0.0,  0.5);
 glEnd();
/* а этот - нет )*/
 painter->fillRect(rect,QBrush(QColor(Qt::yellow)));
}

void QMyGraphicsView::drawBackground( QPainter * painter, const QRectF & rect )
{
 painter->fillRect(rect,QBrush(QColor(Qt::yellow)));

 glColor3f(0.6,0.4,0.0);
 glBegin(GL_TRIANGLES);
  glVertex2f(-0.5, -0.5);
  glVertex2f( 0.5, -0.5);
  glVertex2f( 0.0,  0.5);
 glEnd();
}

void QMyGraphicsView::drawBackground( QPainter * painter, const QRectF & rect )
{
	GLuint glErr = glGetError();
	char* gluErrStr = (char*)gluErrorString(glErr);	

	painter->beginNativePainting();
	glColor3f(0.6,0.4,0.0);
	glBegin(GL_TRIANGLES);
		glVertex2f(-0.5, -0.5);
		glVertex2f( 0.5, -0.5);
		glVertex2f( 0.0,  0.5);
	glEnd();
	painter->endNativePainting();

	painter->fillRect(rect,QBrush(QColor(Qt::yellow)));
}

	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glColor3f(0.6,0.4,0.0);
	glBegin(GL_TRIANGLES);
		glVertex2f(-0.5, -0.5);
		glVertex2f( 0.5, -0.5);
		glVertex2f( 0.0,  0.5);
	glEnd();