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Lab 30: Fl_Progress bar and Timer events (Part I)

1. Description
2. Copying Visual Studio Project
3. Adding widgets in FLUID
4. Adding timer event callbacks
5. How to submit

Description

• In this lab we create a window with a button to animate a progress bar widget:

   

  Part I of the lab adds a timer event, which allows the application to receive notifications at a specific time interval. Part II of the lab the progress bar animation driven by the timer notifications.

   

Copying Visual Studio Project

• The prototype for this project is Lab 4, an empty window:

  
      c255labs\labs\c255_lab04
  
  

• Make a copy of Lab 4 subfolder, or download and unzip c255_lab04.zip

• Rename the new folder as c255_lab30_timer.

• Open solution file in Visual Studio and finish the usual steps to rename the project.

   

Adding widgets in FLUID

• Start FLUID program and open project

  
      c255labs\labs\c255_lab30_timer\fluid_project\CFluidWindow.fl
  
  

• Select Window win_app object in FLUID tree view. Use menu

  
      New/Buttons/Button...
  
  

  Name the new button btn_animate in the properties/C++ dialog.

• Use menu

  
      New/Other/Progress...
  
  

  to add the Fl_Progress bar widget and name it bar_progress in the properties/C++ dialog.

• Save FLUID project and generate C++ code by

  
      File/Write Code...
  
  

   

Adding timer event callbacks

1. Open solution

   
       c255labs\labs\c255_lab30_timer\c255_lab30.sln
   
   

   in Visual Studio.

2. Download the new versions of

   • CMainWindow.h

   • CMainWindow.cpp

3. Compile and test the program.

4. Open CMainWindow.h in the text editor and examine the code:

   • New constant TICK_TIMEOUT specifies the time interval at which the program wants to update the progress bar during the animation. It is a double value specifying the interval in seconds. For example, 0.05 indicates 50 milliseconds.

   • Another constant, DEFAULT_PROGRESS_COUNT indicates progress bar increments between 0% and 100%. For example, an increment of 10 creates progress values

     
         0%, 10%, 20%, 30%, ..., 100%
     
     

   • CMainWindow::callback_btn_animate() is the callback function attached to the button.

   • CMainWindow::callback_animate() is the callback function invoked by the system timer.

5. Open CMainWindow.cpp in the text editor and examine the code:

   • The static member variable CMainWindow::TICK_TIMEOUT must be initialized in the implementation file. Notice the absence of the static keyword in the initialization code. Strangely, using it here is a syntax error, because it conflicts with other C++ rules for the static keyword in the implementation file.

   • Constructor CMainWindow::CMainWindow() initializes the m_progress_count to zero.

   • CMainWindow::show() attaches the callback function to the button widget.

   • When the user clicks "Animate", the CMainWindow::callback_btn_animate():

     • sets the progress count to the default value, and

     • calls CMainWindow::click_btn_animate().

   • CMainWindow::click_btn_animate() calls Fl::add_timeout(), asking FLTK to invoke CMainWindow::callback_animate() after TICK_TIMEOUT seconds.

   • CMainWindow::callback_animate() is called by the timer - this is a one-time timer event. To repeat the event, the function calls the Fl::repeat_timeout(). The "payload" here is the call to CMainWindow::animate(), which does the actual animation.

   • CMainWindow::animate() decrements the m_progress_count. If the progress count becomes zero, the function returns false, and the animation sequence terminates. Otherwise animation sequence continues: the function returns true, the Fl::repeat_timeout() is called again, and the animation sequence continues.

    

How to submit

• This is a self-learning lab. There are no files to submit. Make sure to complete all required steps to build and test the project on your own home computer.