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Source code

#include "mainwindow.h" #include "ui_mainwindow.h"
    MainWindow::MainWindow(QWidget *parent) :
     QMainWindow(parent),
     ui(new Ui::MainWindow)
 {
     ui->setupUi(this);
     connect(ui->pushButton,SIGNAL(clicked()),ui->centralWidget,SLOT(DrawModel())); //DrawModel() can be any other name
     connect(ui->pushButton_2,SIGNAL(clicked()),ui->centralWidget,SLOT(delObject()));	//I have not developed the delObject()
     
 }
  MainWindow::~MainWindow()
 {
     delete ui;
 }

Source code

#include "glwidget.h" #include<GL/glut.h>
 #include <ui_mainwindow.h>

//Set a global
 bool bFlag = false;

   GLWidget::GLWidget(QWidget *parent) :
     QGLWidget(parent)
 {
 }
   void GLWidget::initializeGL()
 {
   //glClearColor(0.2, 0.2, 0.2, 1);  // Background Color
     glShadeModel(GL_SMOOTH);// Enable Smooth Shading
        glClearColor(0.0f, 0.0f, 0.0f, 0.5f);// Black Background
        glClearDepth(1.0f);// Depth Buffer Setup
        glEnable(GL_DEPTH_TEST);// Enables Depth Testing
        glDepthFunc(GL_LEQUAL);// The Type Of Depth Testing To Do
        glEnable ( GL_COLOR_MATERIAL );
        glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
 }
  void GLWidget::resizeGL(int weight, int height)
 {
     glViewport     ( 0, 0, weight, height );
         glMatrixMode   ( GL_PROJECTION );  // Select The Projection Matrix
         glLoadIdentity ( );                // Reset The Projection Matrix
         if ( height==0 )  // Calculate The Aspect Ratio Of The Window
             gluPerspective ( 80, ( float ) weight, 1.0, 5000.0 );
         else
             gluPerspective ( 80, ( float ) weight / ( float ) height, 1.0, 5000.0 );
         glMatrixMode   ( GL_MODELVIEW );  // Select The Model View Matrix
         glLoadIdentity ( );    // Reset The Model View Matrix
  }
   void GLWidget::paintGL()
 {
    }
  void GLWidget::glTriangle(){
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);// Clear Screen And Depth Buffer
         glLoadIdentity();// Reset The Current Modelview Matrix
         glTranslatef(-1.5f,0.0f,-6.0f);// Move Left 1.5 Units And Into The Screen 6.0
               glBegin(GL_TRIANGLES);// Drawing Using Triangles
                 glColor3f(1.0f,0.0f,0.0f);// Set The Color To Red
                 glVertex3f( 0.0f, 1.0f, 0.0f);// Top
                 glColor3f(0.0f,1.0f,0.0f);// Set The Color To Green
                 glVertex3f(-1.0f,-1.0f, 0.0f);// Bottom Left
                 glColor3f(0.0f,0.0f,1.0f);// Set The Color To Blue
                 glVertex3f( 1.0f,-1.0f, 0.0f);// Bottom Right
             glEnd();// Finished Drawing The Triangle
 }
  void GLWidget::glQuard(){
        glTranslatef(3.0f,0.0f,0.0f);// Move Right 3 Units
        glColor3f(0.5f,0.5f,1.0f);// Set The Color To Blue One Time Only
        glBegin(GL_QUADS);// Draw A Quad
            glVertex3f(-1.0f, 1.0f, 0.0f);// Top Left
            glVertex3f( 1.0f, 1.0f, 0.0f);// Top Right
            glVertex3f( 1.0f,-1.0f, 0.0f);// Bottom Right
            glVertex3f(-1.0f,-1.0f, 0.0f);// Bottom Left
        glEnd();// Done Drawing The Quad
  }

void GLWidget::DrawModel()
{
    if(bFlag == false)
    {
        glTriangle();
        bFlag == true;
    }
    else
    {
        glQuard();
        bFlag = false'
    }
}

Source code

connect(ui->pushButton,SIGNAL(clicked()),ui->centralWidget,SLOT(glTriangle()));