BlurWindow.vala

// Compile: valac --pkg=gtk+-3.0 --pkg=gdk-x11-3.0 BlurWindow.vala

[DBus (name = "org.pantheon.gala")]
public interface IGala : Object { 
    public abstract void disable_blur_behind (uint32 xid) throws Error;
    public abstract void enable_blur_behind (uint32 xid, int x, int y, int width, int height, uint8 opacity) throws Error;
}

const string CSS_DATA = """
    window {
        background-color: %s;
        color: #fff;
    }
    
    button {
        color: #fff;
    }
""";


Gtk.Window window;
Gtk.CssProvider provider;
Gtk.ColorButton cbutton;
Gtk.Scale op_slider;

public static int main (string[] args) {
    Gtk.init (ref args);

    window = new Gtk.Window ();
    window.set_visual (Gdk.Screen.get_default ().get_rgba_visual ());
    window.set_default_size (500, 500);
    window.destroy.connect (() => Gtk.main_quit ());
    window.show_all ();

    provider = new Gtk.CssProvider ();
    provider.load_from_data (CSS_DATA.printf ("rgba (255, 255, 255, 0.0)"));
    Gtk.StyleContext.add_provider_for_screen (window.get_screen (), provider, 600);

    var xwin = (Gdk.X11.Window)window.get_window ();
    uint32 id = (uint32)xwin.get_xid ();

    IGala? gala = Bus.get_proxy_sync (BusType.SESSION, "org.pantheon.gala", "/org/pantheon/gala");
    Idle.add (() => {
        gala.enable_blur_behind (id, 0, 0, 0, 0, 255);
        return false;
    });

    op_slider = new Gtk.Scale.with_range (Gtk.Orientation.HORIZONTAL, 0, 1, 0.1);
    op_slider.hexpand = true;
    op_slider.value_changed.connect (set_background);

    cbutton = new Gtk.ColorButton ();
    cbutton.color_set.connect (set_background);

    var blur_switch = new Gtk.Switch ();
    blur_switch.active = true;
    blur_switch.halign = Gtk.Align.START;
    blur_switch.notify["active"].connect (() => {
        if (blur_switch.active) {
            gala.enable_blur_behind (id, 0, 0, 0, 0, 255);
        } else {
            gala.disable_blur_behind (id);
        }
    });


    var animate_button = new Gtk.Button.with_label ("Animate effect opacity");
    animate_button.clicked.connect (() => {
        uint8 current_opacity = 0;
        Timeout.add (10, () => {
            gala.enable_blur_behind (id, 0, 0, 0, 0, current_opacity);
            bool ret = current_opacity < 255;
            current_opacity += 5;
            return ret;
        });
    });

    var grid = new Gtk.Grid ();
    grid.margin = 24;
    grid.column_homogeneous = true;
    grid.column_spacing = 6;
    grid.row_spacing = 6;
    grid.attach (new Gtk.Label ("Enable blur:"), 0, 0, 1, 1);
    grid.attach (blur_switch, 1, 0, 1, 1);
    grid.attach (new Gtk.Label ("Window tint:"), 0, 1, 1, 1);
    grid.attach (cbutton, 1, 1, 1, 1);
    grid.attach (new Gtk.Label ("Background opacity:"), 0, 2, 1, 1);
    grid.attach (op_slider, 1, 2, 1, 1);
    grid.attach (animate_button, 1, 3, 1, 1);

    window.add (grid);
    window.show_all ();

    Gtk.main ();
    return 0;
}

void set_background () {
    Gtk.StyleContext.remove_provider_for_screen (window.get_screen (), provider);

    var c = cbutton.rgba;
    string str = "rgba (%i, %i, %i, %s)".printf ((int)(c.red * 255),
                                                (int)(c.green * 255),
                                                (int)(c.blue * 255),
                                                op_slider.get_value ().to_string ().replace (",", "."));
    provider = new Gtk.CssProvider ();
    provider.load_from_data (CSS_DATA.printf (str));

    Gtk.StyleContext.add_provider_for_screen (window.get_screen (), provider, 600);    
}