FLTK Tutorial by Xu

Report
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 ?
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It’s Free Open Source Software
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It’s cross platform
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It supports OpenGL

It has a graphical user interface builder called FLUID
Install FLTK
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http://www.fltk.org/software.php get source code and unzip it
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Linux/ Unix/ Mac OSX

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Mac Xcode

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./configure && make && make install
Xcode project file can be found in fltk-source/ide/
Windows Visual Studio
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Open fltk-source/ide/VisualC/fltk.sln and build
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In fltk-source copy FL folder to vc/include
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In fltk-source/lib copy all files to vc/lib
Linking
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Visual Studio
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Add fltk.lib, wsock32.lib, comctl32.lib,fltkgl.lib, fltkforms.lib, and fltkimages.lib
(or fltkd.lib, etc.) to linker input
Linux/ Unix
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`fltk-config --use-gl --use-images --use-forms --cxxflags –ldflags`
Widgets
Common FLTK Widgets
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Buttons
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Text box
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Display and receive strings
Valuators

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Includes radio buttons and check boxes
Display and receive numbers
Groups
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Containers such as tabs and group boxes
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Also includes windows and OpenGL windows
FLTK Hello World
40
#include <FL/Fl.H>
20
180
//FLTK global class
100
#include <FL/Fl_Window.H>
#include <FL/Fl_Box.H>
260
Int main(int argc, char **argv)
{
300
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();
}
FLTK Callbacks
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Sets a functions to call when the value of a widget changes
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void functionName(Fl_Widget*, void*)
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Called function passed pointer to the widget that changed and optional
pointer to data
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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
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Subclass an existing widget
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hold a list of child widgets and handle them together
Custom Widget
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Composite widget
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Slider and text box
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When the value of one changes the other is updated
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Will use slider internally to store data
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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();
}
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Widget is a composition so we will inherit Fl_Group
Class CustomWidget : Fl_Group {
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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);
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Our two widgets
private:
Fl_Int_Input*input;
Fl_Slider*slider;
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Slider will store our data
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Current value
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Bounds
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Step size
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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);
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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();
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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);
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Constructor: Data
bounds(1, 100);
value(1);
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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
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Focus events
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Mouse enters/leaves program
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Program gains/loses focus
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Clipboard events
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Widget events
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Activation/deactivation
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Show/hide
Mouse Events
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Button pushed down
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Mouse moved while button pressed (drag)
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Button release
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Mouse moved
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Mouse wheel
Keyboard Events
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Key Up/Down
FLTK Events
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Override int handle(int event)
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Return 0 if event unused
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Return 1 if event used
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Event will continue to be passed around
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);
}

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