[clue-tech] First example Ruby Gtk program

[Dennis J Perkins]

#! /usr/bin/env ruby

# Display the canonical "hello world" message of a first
# program in a new programming language.

# Note that this program has a flaw that manifests itself 
# when shutting down.  Clicking on the close button makes
# the window disappear, but the event loop is still running.
# This solution to this issue will be shown in another example
# program.

# Use Ruby's gtk2 library.
require "gtk2"

# Initialize Gtk.
Gtk.init

# Create the toplevel window,
win = Gtk::Window.new

# Add a title to the program.
win.set_title "Hello World"

# Add a 10-pixel border to the edge of the toplevel window canvas.
win.border_width = 10

# Create a label to display our "Hello world" message.
label = Gtk::Label.new "Hello world"

# Add our newly created label to the toplevel window.
win.add label

# Widgets are not automatically visible, so make them visible now.
# The toplevel window should be made visible last to avoid seeing 
# widgets and the toplevel window change size as the packing manager
# change size as the packing manager figures out the appropriate sizes
# for everything.

label.show
win.show

# Start the event loop.
Gtk.main