my_gl_widget.cpp

#include "my_gl_widget.h"

MyGlWidget::MyGlWidget(QWidget *parent) : QGLWidget(parent)
{

}

void MyGlWidget::initializeGL()
{
    qglClearColor(Qt::black);
}

void MyGlWidget::resizeGL(int w, int h)
{
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glViewport(0, 0, (GLsizei)w, (GLsizei)h);
    glOrtho(0, 100, 100, 0, -1, 1);
}

void MyGlWidget::paintGL()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glBegin(GL_QUADS);

    glColor3f(1, 0, 0);
    glVertex2f(0, 100);

    glColor3f(0, 1, 0);
    glVertex2f(100, 100);

    glColor3f(0, 0, 1);
    glVertex2f(100, 0);

    glColor3f(1, 1, 1);
    glVertex2f(0, 0);

    glEnd();
}