Using the Qt OpenGL example program we introduced in the labs.

You can find it at: /home/jungle/pj/www/453/box/test NOTE: newly commented globjwin.cpp and main.cpp

• The Qt main loop - main.cpp

  (This file will most likely remain unchanged for most of your 453 carreers.)

• Play with Qt and some of the widgets it provides.

  A widget can be thought of as a Window Gadget. For example: the window itself, a slider, button, text box, etc.

  You should reference the documentation for specifics on parameters.

  Be aware of the order of widgets. Their placing in the code in this example has a relationship with their placing in the window.

  • Add a label to the x slider.

    The label class is QLabel You need to add this code: QLabel *labelx = new QLabel(this); labelx->setText("x rot"); labelx->setAlignment( AlignCenter); vlayout->addWidget( labelx ); don't forget to include qlabel.h Change the alignment: label->setAlignment (AlignCenter / AlignLeft / AlignRight etc)

  • Add the labels for y and z rotation.
    
  • Add an LCD number to show the value of rotations.

    The LCD class is QLCDNumber You need to add this code: QLCDNumber *lcdx = new QLCDNumber( 3, this, "lcdx" ); vlayout->addWidget(lcdx); QObject::connect( x, SIGNAL(valueChanged(int)),lcdx,SLOT(display(int)) ); don't forget to include qlcdnumber.h You need to connect the slider signal to the lcd slot: SLOT(display(int). This is an example of a one to many relationship of signals and slots. There is 1 signal (SIGNAL(valueChanged(int)) emitted by the slider when you move it; and 2 slots: * SLOT(setXRotation(int) * SLOT(display(int)) that are executed when the signal is emitted. The first sets the rotation of the object in the openGL window and the second sets the value of degrees in the LCD number display.

  • Add a button that will reset the display, the sliders and the LCD number to 0.

    The button class is QButton This is another example of a many to many relationship. It should reset: * all sliders positions * all lcd numbers * object rotations

  Remember to check the documentation.

  Main

  The main() function is used to perform some initialisation before control is passed to Qt.

  
  int main( int argc, char **argv )
  {
      QApplication a(argc,argv);			
  
      GLObjectWindow w;
      w.resize( 400, 350 );
      a.setMainWidget( &w );
      w.show();
      return a.exec();
  }
  

  Explanation of code:

  
      QApplication a(argc,argv);			
  

  The QApplication class controls the program flow. It is required for any Qt application.

  argc and argv are C/C++ features. They are the number of command line arguments and the array of command line arguments respectively.

  
      GLObjectWindow w;
  

  GLObjectWindow is our class that contains all of the Qt GUI specific code. It opens a window that has a menu, some sliders and an openGL canvas in which to draw our openGL objects.

  
      w.resize( 400, 350 );
  

  w.resize(); sets the initial size size of the window.

  
      a.setMainWidget( &w );
  

  a.setMainWidget(&w) says that the main widget for this Qt application (a) is w the GLObjectWindow.

  
      w.show();
  

  It is possible to have a widget that is not visible at the start of the program, or indeed can be visible or hidden during different parts of a program. We want to be able to see the main widget which is our GLObjectWindow, so we have to show it. Bear in mind that widgets are never visible when they are created, you must show()them for them to be visible.

  
      return a.exec();
  

  This is where main() passes control to Qt. This is the main loop. This is the point of return when the program exits.

  Useful References

  Qt Reference Documentation

  The Qt tutorials

  Qt's classes

  Contact me
  email: pj@cpsc.ucalgary.ca
  Tel:  (403) 220 7041.