I would like to connect QGLWidget widget in Qt to the Main Window UI. Basically, I would like to send a signal to the QGLWidget when user clicks on a button. I have defined a signal and a slot in my MainWindow and GLWidget as follows:

**Signal**


Qt Code: 
  1. class MainWindow : public QMainWindow
  2.         {
  3.         	Q_OBJECT
  4.        ...
  5.         signals:
  6.         	void draw(void);
  7.         ...
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**Slot**

Qt Code: 
  1. class GLWidget : public QGLWidget
  2.         {
  3.         	Q_OBJECT
  4.       ..
  5.         public slots:
  6.          	void updateScreen(void);
  7.              ...
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and in MainWindow.cpp
I do



Qt Code: 
  1. void  MainWindow::on_drawButton_clicked()
  2.         	{
  3.     //do stuff to draw function in paintGL
  4.         	    	emit draw();
  5.                 qDebug()<<"draw emmited";
  6.     ..
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I connect them in MainWindows Constructor as follows..

Qt Code: 
  1. GLWidget *g = new GLWidget;
  2.     connect(this, SIGNAL(draw()), g, SLOT(updateScreen()));
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updateScreen() has a message to let me know if the slot is executed. I tried updateGL() and update()

Qt Code: 
  1. void GLWidget::updateScreen(void)
  2.     		 {
  3.     		 qDebug()<<"I'm Updating!";
  4.     		 updateGL();
  5.     		 update();
  6.     		 }
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The slot is being executed, but the screen is not being updated to reflect the new things I have drawn on the screen

**The screen only update when I resizeGL is called from actions**

I use a temporary fix using a timer..

Qt Code: 
  1. //temporary fix
  2. 	 QTimer *timer = new QTimer(this);
  3. 	 connect(timer, SIGNAL(timeout()), this, SLOT(updateScreen()));
  4. 	 timer->start(1000);
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My GLWidget.cpp file is below..

Qt Code: 
  1. ...
  2.  
  3.         #include "glwidget.h"
  4.         #include "motion.h"
  5.         #include "MainWindow.h"
  6.         #include <GL/glut.h>
  7.  
  8.        ...
  9.          void GLWidget::initializeGL()
  10.         	 {
  11.             glClearColor(1.0,1.0,1.0,1.0);
  12.         	GLUquadricObj *qobj = gluNewQuadric();	
  13.         	gluQuadricDrawStyle(qobj,GLU_FILL);
  14.         	gluQuadricNormals(qobj,GLU_SMOOTH);	
  15.         	glClearDepth( 1.0f );
  16.         	glEnable(GL_DEPTH_TEST);
  17.         	glShadeModel(GL_SMOOTH);
  18.         	double eqn[] = {0.01f,0.0f,0.01f,-1.0f};// enable clip plane	
  19.         	glClipPlane(GL_CLIP_PLANE0,eqn);
  20.         	setupLight();
  21.         	}
  22.  
  23.  
  24.  
  25.         void GLWidget::paintGL()
  26.         	{
  27.  
  28.         	 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  29.         	 glMatrixMode(GL_MODELVIEW);
  30.         	 glPushMatrix();
  31.         	 glLoadIdentity();
  32.         	 glTranslatef(0.0, 0.0, -5.0);
  33.              glRotatef(xRot / 16.0, 1.0, 0.0, 0.0);
  34.              glRotatef(yRot / 16.0, 0.0, 1.0, 0.0);
  35.              glRotatef(zRot / 16.0, 0.0, 0.0, 1.0);
  36.         	 //glTranslated(xTrans / 20.0, yTrans/ 20.0, 0.0f);
  37.         	 glScalef(scale, scale, 1.0); 
  38.         	 m.drawControlFunction();
  39.         	 glPopMatrix();
  40.  
  41.         	 }
  42.  
  43.         //ok for now
  44.         void GLWidget::resizeGL(int w, int h){
  45.  
  46.         	 int side = qMin(w, h);
  47.         	 double ratio = (double)w/(double)h;
  48.              //glViewport((w - side) / 2, (h - side) / 2, side, side);
  49.         	 glViewport (0, 0, (GLsizei) w, (GLsizei) h); 
  50.         	 glMatrixMode(GL_PROJECTION);
  51.              glLoadIdentity();
  52.         	 gluPerspective(70.0f, ratio, 0.1f, 1000.0f);
  53.            //  glOrtho(-15.0, +15.0, -10.0, +15.0, 1.0, 15.0);
  54.  
  55.              glMatrixMode(GL_MODELVIEW);
  56.         	 glLoadIdentity ();
  57.              glTranslatef(0.0f, 0.0f, -10.0f);
  58.         }
  59.  
  60.  
  61.  
  62.           ...
  63.  
  64.         	 void GLWidget::updateScreen(void)
  65.         		 {
  66.  
  67.         		 qDebug()<<"Im working";
  68.  
  69.         			updateGL();
  70.         			update();
  71.         			repaint();
  72.         		 }
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