FLTK Tutorial

Introduction

Installation

Widgets

Handling Event

System events

Mouse events

Keyboard events

Introduction

The Fast Light Tool Kit (“FLTK”, pronounced “fulltick”) is a cross-platform C++ GUI toolkit

FLTK was originally developed by Mr. Bill Spitzak

FLTK website: http://www.fltk.org/index.php

Documentation: http://www.fltk.org/documentation.php

Why FLTK ?

It’s Free Open Source Software

It’s cross platform

It supports OpenGL

It has a graphical user interface builder called FLUID

Install FLTK

http://www.fltk.org/software.php get source code and unzip it

Linux/ Unix/ Mac OSX

./configure && make && make install

Mac Xcode

Xcode project file can be found in fltk-source/ide/

Windows Visual Studio

Open fltk-source/ide/VisualC/fltk.sln and build

In fltk-source copy FL folder to vc/include

In fltk-source/lib copy all files to vc/lib

Linking

Visual Studio

Add fltk.lib, wsock32.lib, comctl32.lib,fltkgl.lib, fltkforms.lib, and fltkimages.lib (or fltkd.lib, etc.) to linker input

Linux/ Unix

`fltk-config --use-gl --use-images --use-forms --cxxflags –ldflags`

Widgets

Common FLTK Widgets

Buttons

Includes radio buttons and check boxes

Text box

Display and receive strings

Valuators

Display and receive numbers

Groups

Containers such as tabs and group boxes

Also includes windows and OpenGL windows

FLTK Hello World#include <FL/Fl.H>

//FLTK global class

#include <FL/Fl_Window.H>

#include <FL/Fl_Box.H>

Int main(int argc, char **argv)

{

Fl_Window *window = new Fl_Window(300, 180);

Fl_Box *box = new Fl_Box(20, 40, 260, 100,

"Hello World");

box->box(FL_UP_BOX);

//tell FLTK that we will not add any more widgets to window

window->end();

//show the window and enter the FLTK event loop:

window->show(argc, argv);

return Fl::run();

}

180

300

20

40

260

100

FLTK Callbacks

Sets a functions to call when the value of a widget changes

void functionName(Fl_Widget*, void*)

Called function passed pointer to the widget that changed and optional pointer to data

Can be activated by keyboard shortcut

Callback Demo

void button_cb(Fl_Widget *widget, void *data)

{

Fl_Button *button = (Fl_Button*)widget;

button->label("Thank you");

}

Int main(int argc, char **argv)

{

...

Fl_Button *button = new Fl_Button(50, 70, 200, 40, "Click Me");

button->callback(button_cb);

...

}

Custom Widgets

Subclass an existing widget

hold a list of child widgets and handle them together

Custom Widget

Composite widget

Slider and text box

When the value of one changes the other is updated

Will use slider internally to store data

Easier because already has min, max, etc.

Main function#include <FL/Fl.H>

#include <FL/Fl_Window.H>

#include "CustomWidget.h"

int main(int argc, char **argv)

{

Fl_Window *window = new Fl_Window(300, 120);

CustomWidget *customWidget = new CustomWidget(50, 50, 200, 20);

window->end();

window->show(argc, argv);

return Fl::run();

}

Widget is a composition so we will inherit Fl_Group

Class CustomWidget : Fl_Group {

Constructor with default FLTK parameters

public:

CustomWidget(int x, int y, int w, int h, char *l =0) : Fl_Group(x, y, w, h, l);

Our two widgets

private:

Fl_Int_Input*input;

Fl_Slider*slider;

Slider will store our data

Current value

Bounds

Step size

Common slider properties

public:

int value();

void value(intv);

int minimum();

void minimum(int min);

int maximum();

void maximum(int max);

void bounds(int min, int max);

Internal callbacks

static void input_cb(Fl_Widget *w, void *d);

static void slider_cb(Fl_Widget *w, void *d);

void input_cb2();

void slider_cb2();

Constructor: Layout

Int const in_w = 40;

input = new Fl_Int_Input(x, y, in_w,

h);

slider = new Fl_Slider(x + in_w, y,

w- in_w, h);

slider->type(FL_HOR_SLIDER);

Constructor: Data

bounds(1, 100);

value(1);

Constructor: Callbacks

//The callback is done each time the text is changed by the user

input->when(FL_WHEN_CHANGED);

input->callback(input_cb, this);

slider->callback(slider_cb, this);

Static callbacks

void CustomWidget::input_cb(Fl_Widget *w,

void *d)

{

((CustomWidget*)d)->input_cb2();

}

void CustomWidget::slider_cb(Fl_Widget *w,

void *d)

{

((CustomWidget*)d)->slider_cb2();

}

Callbacks: Update the other widget

void CustomWidget::input_cb2()

{

Int val;

sscanf(input->value(), "%d", &val);

slider->value(val);

}

void CustomWidget::slider_cb2()

{

char val[16];

sprintf(val, "%d", (int)(slider->value() + 0.5));

input->value(val);

}

Properties

Int CustomWidget::value()

{

return (int)(slider->value() + 0.5);

}

void CustomWidget::value(intv)

{

slider->value(v);

slider_cb2();

}

System Events

Focus events

Mouse enters/leaves program

Program gains/loses focus

Clipboard events

Widget events

Activation/deactivation

Show/hide

Mouse Events

Button pushed down

Mouse moved while button pressed (drag)

Button release

Mouse moved

Mouse wheel

Keyboard Events

Key Up/Down

FLTK Events

Override int handle(int event)

Return 0 if event unused

Event will continue to be passed around

Return 1 if event used

Event is consumed

Slider responds to up/down keys

Int CustomWidget::handle(int event)

{

if ( event == FL_KEYDOWN )

{

if ( Fl::event_key() == FL_Up )

{

value(value() + 1);

return 1;

}

else if ( Fl::event_key() == FL_Down )

{

value(value() - 1);

return 1;

}

}

return Fl_Group::handle(event);

}