Termux FLTK
![fltk window](https://www.fltk.org/doc-1.3/hello_cxx.png)
image from [fltk.org](https://www.fltk.org/).

# Termux Desktop GUI Programming

Howdy folks. This one is a continuation of the previous [tutorial](https://code.sololearn.com/Wu48arwICgth) where I showed how to setup Termux with a desktop environment (xfce4) via a VNC server. So make sure you have the previous tutorial mastered before trying this one.

Here we will see how to code a simple "Hello World" window and then execute it.

We will use **FLTK** (*Fast lightweight ToolKit*), a lightweight open source library for making graphical user interfaces for X.

# Installations
## X11 headers
FLTK library will need X11 installed, which could be already installed when you followed the previous Termux tutorial. The X11 headers might not be installed though, so you will need to install them as well. Run this command:

```
pkg install xorgproto
```
## FLTK
Then we need to install the FLTK library. Run this command:
```
pkg install fltk
```

>The static library version is also available in the termux repo for making statically compiled binaries.
>>``` pkg install fltk-static```
## Xfce Terminal
We will also need a functioning terminal in XFCE desktop environment. So you might want to install this as well:

```
pkg install xfce4-terminal
```

# main.cpp

Let's copy and paste the code from [fltk.org tutorial](https://www.fltk.org/doc-1.3/basics.html)

Create and edit file named **main.cpp**.
This file should contain this: 
```
#include < FL/Fl.H >
#include < FL/Fl_Window.H >
#include < FL/Fl_Box.H >

int main(int argc, char **argv) {
    Fl_Window *window = new Fl_Window(340,180);
    Fl_Box *box = new Fl_Box(20,40,300,100,
    "Hello, World!");
    box->box(FL_UP_BOX);
    box->labelfont(FL_BOLD+FL_ITALIC);
    box->labelsize(36);
    box->labeltype(FL_SHADOW_LABEL);
    window->end();
    window->show(argc, argv);
    return Fl::run();
}

```

# CMakeLists.txt

We use **cmake** to build the **Makefile**.

First we create and edit a file named **CMakeLists.txt**, as such:

```
cmake_minimum_required(VERSION 3.0)

project(hellofltk VERSION 0.0.1)

include_directories(
/data/data/com.termux/files/usr/include)
link_directories(
/data/data/com.termux/files/usr/lib)
link_libraries(fltk)

add_executable(a.out main.cpp)
```

Secondly we build the **Makefile** like so:

```
cmake -H. -B_builds -G "Unix Makefiles"
```

Third, we build the executable:

```
cmake --build _builds
```

There should be an executable named **a.out** in this _builds folder.

(How original for an executable name :) )

# VNC viewer

Now log in the vnc server as shown in the previous tutorial.

Once logged in your desktop display, open a terminal and cd to the directory of the executable **a.out** and execute it as such:

```
./a.out
```

# Voilà

There should be a new window opened that says *[Hello, World!]*.

# Prologue

After this, I hope more people realize how much Linux and C / C++ is a great combination.

More info on **FLTK** at [fltk.org](https://www.fltk.org/).

© Paul Caron, aka ChillPill
Termux FLTK GUI Programming Tutorial
