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About Dialogue

With the Gtk::AboutDialog widget is a easy to provide a user with the information about the application. There are many pieces of information that you can provide about the application. These include the application name, copyright, version, license, authors, document-writers, artists and translators. However, not all applications will have all of these items. The good thing is they are optional. If you do not define them they will simply not show up.


#!/usr/bin/env ruby
require 'gtk2'

authors = ["Author #1", "Author #2"]
documenters = ["Documenter #1", "Documenter #2"]

dialog =

# We are not really handling the error here. The purpose
# of this blockis only to show how it could be done
  logo_book ="/tmp/logo.png")
rescue GLib::FileError => err
  print "I/O ERROR (%s): %s\n" % [err.class, err]
rescue Gdk::PixbufError => err
  print "IMAGE ERROR (%s): %s\n" % [err.class, err]
rescue => err
  print "Unexpected ERROR (%s): %s\n" % [err.class, err]
  raise # re-raise the unexpected error
  dialog.logo = logo_book

# Set application data that will be displayed in the
# main dialog. = "GtkAboutDialog"
dialog.version = "1.0"
dialog.copyright = "(C) 2007 Andrew Krause"
dialog.comments = "All About GtkAboutDialog"

# Set the license text, which is usually loaded from
# a file. Also, set the web site address and label.
dialog.license = "Free to all!" = ""
dialog.website_label = ""

# Set the application authors, documenters and translators.
dialog.authors = authors
dialog.documenters = documenters
dialog.translator_credits = "Translator #1\nTranslator #2"
# NOTE: all these properties are optional
# dialog.artists = ["Artist #1", "Artist #2"]

# dialog.show_all

Before we start discussing the pixbuf let us mention the Gtk::AboutDialog#logo.

Sets a pixbuf displayed as logo in the about dialogue. If this is not set, it defaults to Gtk::Window.default_icon_list. Since 2.6; (see: Gtk::AboutDialog#logo=)
  • logo: A Gdk::Pixbuf displayed as logo for the about dialogue.
  • Returns: logo


Gdk::Pixbuf is a class that contains information about an image stored in memory. It allows you to build images manually by placing shapes or pixels, or load a prebuilt images from a file. We will only be discussing the latter in our tutorial. To load an image from a file you use If you do not specify the size, this method will load the image of with an initial size set to the actual size of the image:, width = nil, height = nil)

Creates a new pixbuf by loading an image from a file. The file format is detected automatically. Possible exceptions are in the Gdk::PixbufError and GLib::FileError.

  • filename: Name of file to load
  • width: The width the image should have or nil for default width. Since 2.4
  • height: The height the image should have or nil for default height. Since 2.4
  • Returns: A newly-created pixbuf, or raise an exception if any of several error conditions occurred:
    • the file could not be opened,
    • there was no loader for the file's format,
    • there was not enough memory to allocate the image buffer, or
    • the image file contained invalid data.

As you can see this method will raise an exception if things go wrong. There are two exception types that you should be concerned about:

Here is a sample of what you can do or how to handle pixbuf related errors:

rescue GLib::FileError => err
  print "I/O ERROR (%s): %s\nCode:%s\nDomain:%s\n" %
       [err.class, err, err.code, err.domain]
rescue Gdk::PixbufError => err
    print "IMAGE ERROR (%s): %s\nCode:%s\nDomain:%s\n" %
       [err.class, err, err.code, err.domain]
rescue => err # This may not be a good idea
  print "Undefined ERROR (%s): %s\n" % [err.class, err]
  raise   # re-raise the unexpected error
  puts "All went well."

The domain and code methods of exception object should provide additional subcategories for the exception. Indeed you should be familiar with error codes, to utilize these programmatically, for instance:

rescue Gdk::PixbufError => err
  if err.code == Gdk::PixbufError::CORRUPT_IMAGE
    print "Your image in file: %s is corupted, please replace it\n" % [file]

Resizing and image interpolation modes

You can resize the image during or after you load its file. You may wish to resize it after reloading, because the method allowing to do it provides image quality control (see: GdkInterpType)

scale(dest_width, dest_height, interp_type = Gdk::Pixbuf::INTERP_BILINEAR)
Create a new Gdk::Pixbuf containing a copy of src(self) scaled to dest_width x dest_height. Leaves src(self) unaffected. interp_type should be Gdk::Pixbuf::INTERP_NEAREST if you want maximum speed (but when scaling down Gdk::Pixbuf::INTERP_NEAREST is usually unusably ugly). The default interp_type should be Gdk::Pixbuf::INTERP_BILINEAR which offers reasonable quality and speed. For more complicated scaling see Gdk::Pixbuf#scale! and Gdk::Pixbuf#composite!.
  • dest_width: the width of destination image
  • dest_height: the height of destination image
  • interp_type: the interpolation type for the transformation. (GdkInterpType
  • Returns : the new Gdk::Pixbuf, or nil if not enough memory could be allocated for it.

This enumeration describes the different interpolation modes that can be used with the scaling functions. Gdk::Pixbuf::INTERP_NEAREST is the fastest scaling method, but has horrible quality when scaling down. Gdk::Pixbuf::BILINEAR is the best choice if you are not sure what to choose, it has a good speed/quality balance.

Note : Cubic filtering is missing from the list; hyperbolic interpolation is just as fast and results in higher quality.

  • INTERP_NEAREST : - Nearest neighbor sampling; this is the fastest and lowest quality mode. Quality is normally unacceptable when scaling down, but may be OK when scaling up.
  • INTERP_TILES : - This is an accurate simulation of the PostScript image operator without any interpolation enabled. Each pixel is rendered as a tiny parallelogram of solid color, the edges of which are implemented with antialiasing. It resembles nearest neighbor for enlargement, and bilinear for reduction.
  • INTERP_BILINEAR : - Best quality/speed balance; use this mode by default. Bilinear interpolation. For enlargement, it is equivalent to point-sampling the ideal bilinear-interpolated image. For reduction, it is equivalent to laying down small tiles and integrating over the coverage area.
  • INTERP_HYPER : - This is the slowest and highest quality reconstruction function. It is derived from the hyperbolic filters in Wolberg's "Digital Image Warping", and is formally defined as the hyperbolic-filter sampling the ideal hyperbolic-filter interpolated image (the filter is designed to be idempotent for 1:1 pixel mapping).

Help Menu Option

The About Dialogue usually appears an a Help Menu, which makes this point as good as any to mention how to handle Help menu option itself. We will not talk about the complete solution here, because menus will not be covered until chapter (9) "Menus and Toolbars". What is worth mentioning here is that help can come in many text formats which on top of that are handled on different platforms with different applications.

Let me start with an oxymoron: In order to handle "Help" in a platform independent manner we need to figure out on which platform our application is running. If we are interested only in the major three OS families such as Unix/Linux, OS X, and Microsoft Windows we can pull it off with something like the following code:

class DisplayHelp
  def self.print(file)
      when /ix/i, /ux/i, /gnu/i, /sysv/i, /solaris/i, /sunos/, /bsd/i
        system "xdg-open #{file}"   # Unix/Linux
      when /win/i, /ming/i
        system "start #{file}"      # Microsoft Windows
      when /universal-darwin/
        system "open #{file}"       # Apple's osx
        raise "Unknown operating system: [#{RUBY_PLATFORM}]"

# Main program
if __FILE__ == $0

The above code opens any reasonable file format even images and text files with os-specific application. The following table may give you a better idea:

O.S.     | Command             *.txt, *.html, *.pdf, *.png, ...
Windows  | start   ..... start index.html,       or:   start some.pdf
OSX      | open ........ open index.html,        or:   open some.pdf
Linux    | xdg-open .... xdg-open index.html,    or:   xdg-open some.pdf
Last modified:2009/03/10 06:24:44
References:[tut-gtk2-dialog] [tut-gtk]