#include <QGLWidget>
 
class GLWidget : public QGLWidget
{
	Q_OBJECT
	public:
		GLWidget(QWidget *parent = 0);
	protected:
		void paintGL(); //paintEvent on all windows
		void resizeGL(int width, int height);//event called if you resize the window
};
 

 
#include <QtGui>
#include <QtOpenGL>
#include <math.h>
 
#include "glwidget.h"
 
GLWidget::GLWidget(QWidget *parent):QGLWidget(parent){}
 
void GLWidget::paintGL()
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	glLoadIdentity();
 
	glTranslated(0.0, 0.0, -10.0);
	glBegin(GL_POLYGON);
	glColor3d(100,0,0);
	glVertex2d(1,1);
	glVertex2d(1,-1);
	glVertex2d(-1,-1);
	glVertex2d(-1,1);
 
	glEnd();
	glFlush();
}
 
void GLWidget::resizeGL(int width, int height)
{
	int side = qMin(width, height);
 
	glViewport((width - side) , (height - side), side, side);
	glClearColor(0,234,0,255);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(-3.0, +3.0, +3.0, -3.0, 0.0, 30.0);
	glMatrixMode(GL_MODELVIEW);
}
 

 
 
#include "glwidget.h"
 
int main(int argc, char *argv[])
{
	QApplication app(argc, argv);
	GLWidget glw;
	glw.show();
 
	return app.exec();
}