FLTK Fl_Input / Fl_Output Example

// FLTK Input and Output Example
// by Jonathan Metzgar
// CC-By-Attribution License
//
// This program will initialize a Fl_Input widget and a Fl_Output widget
// The program also creates two buttons: one to quit the program and one to
// process the data. The Model-View-Controller pattern is used to separate
// data from the GUI.

#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Box.H>
#include <FL/Fl_Input.H>
#include <FL/Fl_Output.H>
#include <FL/Fl_Button.H>

#include <string>
#include <iostream>
#include <map>


//////////////////////////////////////////////////////////////////////
// E X T E R N A L   L I B R A R I E S ///////////////////////////////
//////////////////////////////////////////////////////////////////////


#pragma comment(lib, "fltk.lib")
#pragma comment(lib, "comctl32.lib")


//////////////////////////////////////////////////////////////////////
// S T R U C T S /////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////


struct Model
{
    std::string input;
};


struct View {
    Fl_Input* input = nullptr;
    Fl_Output* output = nullptr;
};


//////////////////////////////////////////////////////////////////////
// G L O B A L   V A R I A B L E S ///////////////////////////////////
//////////////////////////////////////////////////////////////////////


Model model;
View view;


//////////////////////////////////////////////////////////////////////
// P R O T O T Y P E S ///////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////


void TransformData(const std::string& input, std::string& output);
void OnInputChanged(Fl_Widget* w, void* userdata);
void OnProcessClicked(Fl_Widget* w, void* userdata);
void OnQuitClicked(Fl_Widget* w, void* userdata);
Fl_Window* CreateWindow();


//////////////////////////////////////////////////////////////////////
// C A L L B A C K S /////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////


void OnInputChanged(Fl_Widget* w, void* userdata) {
    // check for NULL pointer
    if (!view.input) return;

    // The value() method of Fl_Input will return a C-style
    // string which we can use with a std::string
    model.input = view.input->value();
}


void OnProcessClicked(Fl_Widget* w, void* userdata) {
    if (!view.output) return;

    // This is where we can process the input in some way
    std::string transformed;
    TransformData(model.input, transformed);

    // Note 1: We call c_str() method from std::string to get
    // a C style Null terminated string
    // Note 2: the value(string) method of Fl_Output is used
    // to set the current value
    view.output->value(transformed.c_str());
}


void OnQuitClicked(Fl_Widget* w, void* userdata) {
    // We expect userdata to be the Window
    if (!userdata) return;

    // Cast the void* pointer back to a Fl_Window* pointer
    Fl_Window* window = (Fl_Window*)userdata;

    // The hide() method will close the window
    window->hide();
}


//////////////////////////////////////////////////////////////////////
// F U N C T I O N S /////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////


// TransformData(input, output) simply adds " transformed" to the input
// string
void TransformData(const std::string& input, std::string& output) {
    output = input + " transformed!";
}


Fl_Window* CreateWindow() {
    Fl_Window* window = new Fl_Window(640, 480);
    Fl_Box* box = new Fl_Box(20, 40, 600, 100, "Input/Output Example");
    box->box(FL_UP_BOX);
    box->labelfont(FL_BOLD + FL_ITALIC);
    box->labelsize(36);
    box->labeltype(FL_SHADOW_LABEL);

    // We use these to ensure adequate spacing of widgets
    const int x = 100;
    int y = 160;
    const int w = 100;
    const int h = 25;
    const int Spacing = 10;

    view.input = new Fl_Input(x, y, 2 * w, h, "Input");
    y += h + Spacing;
    view.output = new Fl_Output(x, y, 2 * w, h, "Output");
    y += h + Spacing;

    Fl_Button* processBtn = new Fl_Button(x, y, w, h, "Process");
    y += h + Spacing;
    Fl_Button* quitBtn = new Fl_Button(x, y, w, h, "Quit");

    // Register callbacks
    view.input->callback(OnInputChanged, nullptr);
    processBtn->callback(OnProcessClicked, nullptr);
    quitBtn->callback(OnQuitClicked, (void*)window);

    window->end();
    return window;
}


int main(int argc, char** argv) {
    Fl_Window* window = CreateWindow();
    window->show(argc, argv);
    return Fl::run();
}