demo-c.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- 
All application entry points should start with `app`
You can defined aliases for namespaces in here.  
XML namespaces are not fully supported in general, just these three special cases:
- `vs.fltk` for the fltk widgets, `fl` by default
- `vs.templ` for the static templates, `s` by default
- `vs.core` for core features, no prefix set by default.
 -->
<app xmlns:fl="vs.fltk">
    <fl:window box="0,0,320,240" label="Demo Counter (C)">
        <!-- 
        Mixins allow you to reuse props as a baseline for multiple instances. 
        In this case for all fl:buttons covered in this scope
        -->
        <mixin name="+fl:button" bg.colour="#aa3300" label.colour="#99ee4f" />

        <!--
        Instead of having a script for every single button, it is better to group their callbacks into one,
        even more so when logically related.
        -->
        <script lang="c">
        <![CDATA[ 
        unsigned int counter = 0;

        void _update(){
            static char str_buf[32];
            itoa(counter,str_buf,10);
            $$prop($("main-text"),"label",str_buf);
        }

        void on_add(){
            counter++;
            _update();
        }

        void on_dec(){
            counter--;
            _update();
        }

        /* Register the previous functions as callbacks.
         * Registration is needed to expose symbols outside a script.
         * Each language has its own mechanisms to do that.
         */
        $cb(on_add);
        $cb(on_dec);
        ]]>
        </script>

        <fl:label name="main-text" label="0" label.size="90" box="20,20,280,120" />
        <fl:button label="Add" on.callback="on_add" box="20,160,80,50" />
        <fl:button label="Remove" on.callback="on_dec" box="120,160,80,50" />
        <fl:button label="Console" box="220,160,80,50">
            <script lang="c" compact="true">
                //The compact form of a C script automatically wraps your code
                //as the default callback. Not every language supports a compact form.
                $log(LOG_LOG,"Hello world!");
            </script>
        </fl:button>
    </fl:window>
</app>