CSC/ECE 517 Fall 2010/ch1 S10 MM
Introduction
A GUI toolkit is a set of widgets and APIs that can be used and extended to construct a graphical user interface application. At a minimum a GUI toolkit will provide generic graphical widgets to display to the screen, and an eventing system to tie interactive widget pieces with other widgets, or to a data model. Most toolkits will provide widget containers for easy layouts, abstract data model types and containers, and an easy to use mechanism for implementing an observer pattern for linking widgets and data structures. Advanced toolkits, such as Qt, will even offer convenience widgets for advanced data display, concurrent programming abstractions, or even a whole browser backend (based on Webkit, in Qt's case). Ideally a toolkit would work across several different operating systems with very minimal changes to the application code or compilation process.
Most GUI toolkits are natively composed in C++. Object-oriented language features are all but required for the level of base functionality extension required in a large GUI systems. In many cases, though, bindings for the toolkit will spring up in different languages, and usually the most useful bindings will be in a dynamic scripting language such as Python, or Ruby. This page will talk about several GUI toolkit bindings in the Ruby language.
Dynamically typed languages offer many different advantages for GUI development. Since GUIs typically work with many different simple and composite data types, and the toolkit itself adds a large number of class types on top of that, defining class interfaces and usable data structures, and making them available to the right widgets at the right time within the application can be tedious in statically typed languages. Dynamic languages offer the ability to define, and redefine these things, allowing very rapid development.
The only downside to coding with the dynamic languages is that the speed of the application will suffer due to interpreter overhead, but even for large applications this may be acceptable if the application does not require a particularly high frame rate under heavy load. Logistically, however, in many cases there are problems with the level of support and maintenance in a particular binding project. It is always useful to look at when the last version control checkin was made for a project if that is available, and try to compare the latest binding release date with the latest native implementation release date. Also, it is usually harder to find documentation for the specific dynamic language that you are using, and you may be stuck reading C++ API documentation, and potentially source code for the project when you hit something you did not expect. There are also usually slight complications with deployment, and there may be licensing discrepancies between the C++ and Python/Ruby versions as well.
Overview of Ruby GUI Toolkits
Ruby/Tk
Tk is an older GUI toolkit, originally written in Tcl. Tk offers a good set of generic widgets, widget containers for relatively easy layouts, a Canvas, and event binding. Unfortunately none of these features are very advanced, and they're generally quirky to use once you've used either a wxWidgets base system or a Qt system. For example, Tk appears to only give you a single callback or variable binding for widget output and events, instead of providing a more robust mechanism for observing data changes through events or signals. You could roll your own mechanism with those features, but that could get tedious in a hurry. Also, the widgets are drawn in a distinctly Tk-style, instead of in the native style of the OS. It is highly desirable for a production GUI application to offer the standard idioms that a user expects in a native OS application, so Tk probably should never be used for a globally deployed application.
Example
Pros and Cons
QtRuby
Qt is well-supported open source GUI toolkit that is available under the LGPL license. QtRuby attempts to offer the vast array of functionality provided by Qt in Ruby form.
Unfortunately it appears that QtRuby is not being actively maintained, as the last release was in August of 2009.
Example
Advantages of a Dynamic Language
Pros and Cons
wxRuby
wxWidgets is a very popular GUI toolkit as it has been under an open license resembling the LGPL for much longer than Qt. It is entirely open source and never developed exclusively by a for-profit company. Documentation for wxWidgets is generally very good, although a lot of documentation for wxPython is generally found when hitting google.
Example
Pros and cons
Other GUI toolkits
- FXRuby
- Ruby-GNOME2
- Shoe