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Lab 6: Fl_Box, Fl_Image, Fl_JPEG_Image

1. Description
2. Copying Visual Studio Project
3. Adding widgets in FLUID
4. Adding button callback function
5. How to submit

Description

• FLTK classes Fl_Box and Fl_Image provide facilities to load and draw images in FLTK. In this lab we will display Joint Photographic Experts Group (JPEG) file. The Fl_JPEG_Image class supports loading, caching, and drawing of JPEG and File Interchange Format (JFIF) images.

• When user clicks the button, the callback function will load, resize, and draw the image inside the Fl_Box widget:

   

   

Copying Visual Studio Project

• The prototype for this project is Lab 4:

  
      c255labs\labs\c255_lab04
  
  

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

• Rename the new folder as c255_lab06_jpeg.

• 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_lab06_jpeg\fluid_project\CFluidWindow.fl
  
  

• Use FLUID menu or Widget Bin to add the widgets to your window. Select Window win_app object in FLUID tree view. Use menu

  
      New/Other/Box
  
  

  to add Fl_Box widget to the window. It appears in the design view as a square box.

• In the properties window, name the widget as box_jpeg_image.

• Add a push button,

  
      New/Buttons/Button
  
  

• Name the button in the Properties/C++ as btn_show_text and btn_show_jpeg.

• Specify button label in Properties/GUI as "Show JPEG"

• Save FLUID project and generate C++ code by

  
      File/Write Code...
  
  

   

Adding button callback function

1. Open solution

   
       c255labs\labs\c255_lab06_jpeg\c255_lab06.sln
   
   

   in Visual Studio.

2. Open CMainWindow.h in text editor. Add NEW callback code as shown:

   
   // CMainWindow.h
   
   #ifndef _CMAINWINDOW_H_INCLUDED_
   #define _CMAINWINDOW_H_INCLUDED_
   
   #include "../fluid_project/CFluidWindow.h"
   
   // NEW
   #include <FL/Fl_Shared_Image.H>
   #include <FL/Fl_JPEG_Image.H>
   
   class CMainWindow : public CFluidWindow {
       Fl_Image* jpeg_image;       // NEW
   public:
       CMainWindow();              // NEW
   
       void show();
       void click_btn_show_jpeg(); // NEW
   
       // callback functions
       static void callback_window_closing(Fl_Widget* widg, void* userdata_);
   
       // NEW
       static void callback_btn_show_jpeg(Fl_Widget* widg, void* userdata_);
   };//class CMainWindow
   
   #endif // _CMAINWINDOW_H_INCLUDED_
   
   

3. Notice that the CMainWindow class has the data member

   
       Fl_Image* jpeg_image;
   
   

4. Open CMainWindow.cpp in the text editor.

5. Download the new version of CMainWindow.cpp , or add NEW code manually:

   
   // Lab 6: Fl_Box, Fl_Image, Fl_JPEG_Image
   // CMainWindow.cpp
   
   #include "CMainWindow.h"
   
   // NEW
   CMainWindow::CMainWindow()
       : jpeg_image( nullptr )
   {
   }
   
   void CMainWindow::show()
   {
       // Window callbacks:
       win_app->callback( (Fl_Callback*)CMainWindow::callback_window_closing, (void*)(this) );
   
       // NEW
       btn_show_jpeg->callback( (Fl_Callback*)CMainWindow::callback_btn_show_jpeg, (void*)(this) );
   
       // Make the window visible:
       win_app->show();
   }
   
   // callback functions
   void CMainWindow::callback_window_closing(Fl_Widget* widg, void* userdata_) {
       std::cout << "X button clicked -- exiting the program\n";
       while( Fl::first_window() ) {
           Fl::first_window()->hide();
       }
   }
   
   // NEW
   void CMainWindow::callback_btn_show_jpeg(Fl_Widget* widg, void* userdata_)
   {
       CMainWindow* win = static_cast< CMainWindow* > ( userdata_ );
       win->click_btn_show_jpeg();
   }
   
   // NEW
   void CMainWindow::click_btn_show_jpeg()
   {
       std::cout << "btn_show_jpeg click\n";
       Fl_JPEG_Image* jpeg_image_orig = new Fl_JPEG_Image( "../../JPEG/bird.JPG" );
       // copy allow us to resize the image:
       jpeg_image = jpeg_image_orig->copy( box_jpeg_image->w(), box_jpeg_image->h() );
       delete jpeg_image_orig;
       box_jpeg_image->image( jpeg_image );
       win_app->redraw();
   }
   
   

6. Compile and test the program.

    

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.