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FLTK 1.3.0 Tutorial This a tutorial can be used by the absolute FLTK beginner. In the course of the tutorial the most common widgets will be explained and you will gain a good overview of the FLTK toolkit. The examples have been kept as short and simple as possible so it will not take a lot of time to understand them. I ported FLTK to DOS and took the screenshots in DOS. The examples will work without any changes on any platform FLTK can be used for. Contents 1. Introduction 2. The FLTK structure 3. Installation of the FLTK toolkit 4. The first program 5. The button widget 6. Callback functions 7. Input and Output boxes 8. The editor widget 9. The browser widget 10. The menubar widget 11. Toolbar and drop-down list 12. A dialog window with radio buttons 13. Displaying images 14. Grouping widgets in Tabs 15. Handling mouse events part1 16. Handling mouse events part2 17. Displaying the events generated by FLTK 18. The tree widget 19. References

1. Introduction FLTK shall stand for Fast Light ToolKit and is a GUI written in C++ for C++ programs. It can be used on Linux, Windows, Apple Mac and DOS. FLTK has lower memory requirements than other toolkits and can be linked as a static library with an application. It can also be compiled as a shared library too. FLTK has been in development over many years and the currently latest version is 1.3.0. There had been a version 2.0 before but unfortunately this branch never got out of alpha and development of that has been canceled now in favor of version 1.3.0. So 1.3.0 is the version any new development should be based on. 2. The FLTK structure Being written in C++ FLTK defines a class for every widget. GUI toolkits usually refer to all sorts of objects, like buttons, input boxes, scrollbars etc as widgets. The base class for all widgets is the Fl_Widget class. All widgets are subclasses from the Fl_Widget class or again subclasses from these subclasses. This are some of the direct subclasses of Fl_Widget: Fl_Box, Fl_Button, Fl_Group, Fl_Input_, Fl_Menu_, Fl_Progress and Fl_Timer. A subclass of Fl_Group again is Fl_Window, a class you will be using in every program. An example of a long tree of subclasses is FL_Radio_Round_Button. As shown below this button type is a subclass of Fl_Round_Button which is a subclass of Fl_Light_Button which is again a subclass of Fl_Button. The FL_Radio_Round_Button class has access to all methods or functions defined in one of the classes it is a subclass of. You will have to check in the documentation whether any of these classes has a method which does what you want to achieve. There is also the FL global (static) class containing state information and global methods for the current application. In addition several non-class functions and symbols are provided, they are grouped into

header files with lower-case names. 3. Installation of the FLTK toolkit a.) Linux download the latest source, unpack it and then do configure,make,install. Then compile your program e.g. as: "fltk-config' --compile example.cxx" or if you use images: "fltk-config --use-images --compile example.cxx" Further details can be found in the FLTK manual here: http://www.fltk.org/doc-1.3/basics.html There is a section called "Compiling Programs with Standard Compilers" further below on that page. You can also read the README.Unix.txt file that is included in the FLTK source code package. This also covers using FLTK with the Code::Blocks IDE. b.) Windows There are a number of alternatives to develop FLTK programs on Windows. The FLTK site just has the source code so you either compile FLTK on Windows or download binaries from the net as described below. b1.) DEV-CPP This is an IDE which uses MinGW to generate C and C++ programs on Windows. You can download it here: http://www.bloodshed.net/dev/devcpp.html Then you can download a "devpak" of FLTK 1.3.0 here: http://nanox-microwindows-nxlib-fltk-for-dos.googlecode.com/files/fltk-130-1gp.DevPak After starting DEV-CPP select "Tools" from the menu and "Package Manager". In there select "Install" and open the downloaded DevPak to install it. Then open a new project (File->New->Project), select the "GUI" tab and in there select "FLTK". After a few questions how to name the project and the program file this will come up with the default FLTK program which you can build and run by entering "F9". b2.) Code::Blocks This is another good IDE using MinGW. If you open a new project, you can select the FLTK icon in there. After that you will have enter the location of the FLTK files. You can download the binaries here: http://code.google.com/p/fltkwinbin/downloads/list and then put them into a directory of your choice. Then enter that path into the Code::Blocks' input box. Code::Blocks just needs the path to the root FLTK directory where bin, include, lib, share and test are in. You can then select file->new->empty file and save that as main. Then cut and past one of the examples in this tutorial into the edit window and save the file.

Then right-click on the project, select "Build options" and add the following libraries to the linker settings: libcomctl32.a, libcomdlg32.a, libole32.a,libgdi32.a and libuuid.a. You find these libraries in the "CodeBlocks\MinGW\lib\" directory. After this select Build->Run or CTRL-F10 that should build the project and run it. b3.) Compile FLTK on Windows with MinGW. Both DEV-CPP and Code::Blocks install MinGW on your PC. If you install MinGW after you already have installed one of these IDEs Windows will point to the new MinGW directory and and that causes problems with DEV-CPP. Details how to compile FLTK with MinGW are in the file README.MSWindows.txt which is included in the FLTK source code package. It also described in there how to use FLTK with Cygwin. You can also compile FLTK on Windows with Code::Blocks if you follow this tutorial: http://gintasdx.althirius-studios.com/2011/08/tutorial-codeblocks-with-fltk.html b4.) Microsoft Visual C++ This is covered in the file README.MSWindows.txt. Further details can also be found here: http://research.cs.wisc.edu/graphics/Courses/559-f2009/Main/Tutorial1 c.) Apple OS X Please read the file README.OSX.txt which is included in the FLTK source code package. d.) DOS Download the DJGPP package from http://code.google.com/p/nanox-microwindows-nxlib-fltk-for-dos/downloads/list , edit the start.bat file in there to your paths. The required FLTK libraries are already included in the DJGPP package but can be downloaded from that site separately as well. You can compile the examples either with this line (observe the line wrap here): gpp -g -I/djgpp/include -o example.exe example.cxx -L/djgpp/lib -lfltk -lNX11 -lnano-X -lfreetype For the examples which load an image you have to add additional parameters to this line: gpp -g -I/djgpp/include -o ex13.exe ex13.cxx -L/djgpp/lib -lfltk_images -lfltk -lNX11 -lnano-X -lfreetype -ljpeg -lpng -lz Or you enter a shell with "sh" and use the "fltk-config" script: sh-2.04$ 'fltk-config' --compile example.cxx sh-2.04$ 'fltk-config' --use-images --compile example.cxx

4. The first program This tutorial starts with very simple examples. Some readers may consider them too simple but those may read these parts more quickly. Our first program just opens a window with a title. You can terminate the program by closing the window with your mouse or pressing the ESC key. To run this or any other example please copy the lines below and paste them into the editor that you will use for compiling the code. #include #include int main() { Fl_Window win(400, 400,"FLTK Tutorial - Example 1"); // Display the window // Create a window - width, height, label (=title) win.show(); // Run and return return Fl::run(); } All programs must include the file to include the FLTK global class FL. In addition the program must include a header file for each FLTK class it uses, in our case it is just Fl_Window, a subclass of Fl_Group. The statement: Fl_Window win(400, 400,"FLTK Tutorial - Example 1"); creates a new object of the Fl_Window class called "win". The call also defines the size of the window to be created and the title string. Then there is a call the "show" method of the Fl_Window class to display the window: win.show(); Finally every FLTK program has to have the Fl::run() statement: return Fl::run(); This enters the FLTK event loop. The program now waits for events, like mouse clicks or keystrokes to happen and act upon them. When the window is closed or the ESC key pressed, this function will return.

5. The button widget Here are two examples that add a button to the window made in the example above. The first one extends the example above while the other defines a subclass of FL_Window which gives the code a completely different structure. #include #include #include int main(int argc, char **argv) { // Create a window - width, height, label (=title) Fl_Window *win = new Fl_Window(340,180,"FLTK Tutorial - Example 2"); // Set color of window to white win->color(FL_WHITE); // Begin adding children to this window win->begin(); //Create a button - x , y , width, height, label Fl_Button *button1 = new Fl_Button(25,15,140,40,"OK"); // Set color of button to red button1->color(FL_RED); // Stop adding children to this window win->end(); // Display the window win->show(); // Run and return return Fl::run(); } Since we are using a new widget here, the button widget, we have to include a header file for that class first. The statement: Fl_Window *win = new Fl_Window(340,180,"FLTK Tutorial - Example 2"); creates a pointer to the new window object "win". This is different to the first example and we will have to use "win->show();" now instead of "win.show();" as before. Then we use a "set" method to turn the color of our window to white: win->color(FL_WHITE); FLTK usually has a corresponding "get" method for each "set" method. Here "Fl_color c = win->color();" would return the current window color in "c". Then there is: win->begin(); that tells FLTK to start a group of children for our "win" object. This statement could be

omitted and FLTK will add this implicitly then. Following that we create a pointer to a new button object: Fl_Button *button1 = new Fl_Button(25,15,140,40,"OK"); and make a "set" statement to set its color to red. The statement win->end(); will tell FLTK that we are done defining the children for the "win" object. The defined group will be set to the parent of the window, in this case to NULL because "win" does not have a parent. The following statements will cause the window to be displayed and enter the FLTK event loop. So far we have not defined classes in the examples. To show how this can be done using FLTK classes and inheritance we rewrite the example above: #include #include #include class MyWindow : public Fl_Window { public: MyWindow(int width, int height, const char* title=0) : Fl_Window(width,height,title) { // Set color of window to white color(FL_WHITE); // Begin adding children to this window begin(); //Create a button - x , y , width, height, label Fl_Button *button1 = new Fl_Button(25,15,140,40,"OK"); // Set color of button to red button1->color(FL_RED); // Stop adding children to this window end(); // Display the window show(); } }; int main() { // Create a window with our new class - width, height, label (=title) MyWindow win(340,180,"FLTK Tutorial - Example 2++"); // Run and return return Fl::run(); } Here the statement class MyWindow : public Fl_Window creates a class called MyWindow which is derived from the Fl_Window class. In the constructor of this class we define the color of the window, the button as a child of the window and display the window. Since the "this" pointer is implicit, you do not need a pointer in front of the begin(), end() and show() statements.

In the main function we just create a new object of the MyWindow class called "win" and then enter the FLTK event loop. 6. Callback functions Now we will add a callback function which will be called by FLTK as soon as the button is clicked. This callback function will then change the color of the button. There is no screenshot provided since it looks like the one in the previous example. #include #include #include void button1_cb(Fl_Widget* buttonptr){ if (buttonptr->color() == FL_BLUE) { buttonptr->color(FL_RED); //toggle }else { buttonptr->color(FL_BLUE);//toggle } } int main(int argc, char **argv) { // Create a window - width, height, label (=title) Fl_Window *win = new Fl_Window(340,180,"FLTK Tutorial - Example 3"); // Begin adding children to this window win->begin(); //Create a button - x , y , width, height, label Fl_Button *button1 = new Fl_Button(25,15,140,40,"Click me!"); button1->color(FL_RED); //register callback function with this button button1->callback(button1_cb); win->color(FL_WHITE); // Stop adding children to this window win->end(); // Display the window win->show(); // Run and return return Fl::run(); } The statement: button1->callback(button1_cb); defines that the callback "button1_cb" will be called when the user clicks on it. This function is defined as void button1_cb(Fl_Widget* buttonptr) Please observe that a pointer to the Fl_Widget class is passed and not to Fl_Button. This way we can only use methods defined in Fl_Widget. For this example this is fine since we will only be using the "color" method defined in Fl_Widget. If we want to use methods defined in the Fl_Button class we will have to cast the buttonptr to a Fl_Button class e.g: Fl_Button* b = (Fl_Button*)buttonptr; The rest of the function checks if the button color is blue and if yes turns it to red and vice versa.

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