Cross-platform UI with Qt4 and Ruby - Mac/Linux HOWTO
Today I’ve spent the day working on figuring out how to make UIs using Ruby and Qt4. If you haven’t heard of it, Qt4 is an awesome UI framework written in C++. Since C++ is way too much work, some great KDE devs wrote a bindings generator for Qt4 called qt4-qtruby. While this package is fairly “linuxy”, it’s pretty easy to build it on Mac OS X too, making it possible to write GUI programs for OS X without having to delve into RubyCocoa which has too much hackiness (in my opinion), or even worse, Objective C. Furthermore, your code that you write on OS X will look great on Windows and Linux too!
Starting from scratch
First, install Ruby. If you’re using Linux, you’ll probably use the package manager to install Ruby and the Ruby development libraries! (Ubuntu will run sudo apt-get install ruby irb ruby-dev) OS X Tiger ships with Ruby by default, but you’ll want to install an updated version, via the Ruby one-click installer, then disable the old Ruby by using the following command:
## Only do this on Mac! Linux doesn’t need this nonsense ##
touch ~/.bashrc && echo ‘export PATH="/usr/local/bin:$PATH"’ >> ~/.bashrc
sudo mv /usr/lib/libruby.1.dylib /usr/lib/_libruby.1.dylib
Installing Qt4 and QtRuby
First, install Qt4 by using your package manager on Linux (in Ubuntu, use the -kdecopy packages, they are more up to date), or by downloading the DMG from the Qt/Mac Open Source Edition Download page. You’ll also need MacPorts (and by proxy, the XCode tools). Also, download the Qt4 Ruby bindings source code from Rubyforge and save it to the Desktop.
Here’s the cool thing about QtRuby, and the advantage of building it from source: the build framework for QtRuby scans through whatever version of Qt you have installed, and dynamically builds the bindings. This means, there’s no waiting for new Qt features to be available in Ruby, it’s always up-to-date! Which is quite handy, because it seems like every minor version of Qt has new cool stuff.
Next, we have to do a bit of hackery - unfortunately, there’s no easy way to install QtRuby but it’s not so hard. Here’s what you’ll run:
cd ~/Desktop
sudo port install cmake ## CMake is a cool build system
tar -xzvf qt4-qtruby-1.4.9.tgz && cd ./qt4-qtruby-1.4.9
cmake .
make && sudo make install
Try it out!
Once you’ve got it built, try this sample code to see some of the new features in Qt 4.3 - this code will run a natively-styled wizard in Windows, Mac, and Linux without any changes! Unfortunately, this code isn’t very elegant or Ruby-like, but it’s a base that someone could write a really elegant UI framework over like RoR.
require ‘Qt’
a = Qt::Application.new(ARGV)
def create_intro_page
page = Qt::WizardPage.new do |p|
p.title = "Introduction"
end
label = Qt::Label.new("This is a wizard!")
label.word_wrap = true
layout = Qt::VBoxLayout.new do |v|
v.add_widget(label)
end
page.layout = layout
page
end
wiz = Qt::Wizard.new do |x|
x.add_page(create_intro_page())
x.set_window_title("Test Wizard")
x.show
end
a.exec
 On Mac OS X |
 On Linux |
In summary:
- Install a Ruby that doesn’t suck, and hack your environment so it works right
- Install Qt and MacPorts
- Build QtRuby and install it
- Make UIs for all 3 platforms without hating your life
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Rasmus said,
July 25, 2007 @ 7:12 am
I wish all guides to installing stuff on Mac would be like this one.
Shadowfiend said,
July 27, 2007 @ 5:14 pm
It bears mentioning that the actual bindings generator sitting behind this is Smoke (written in Perl) -- Smoke is actually capable of generating bindings for many different languages, on top of which certain additional customizations are added for the particular language. This tool is what is used to generate most of the Qt and KDE bindings, including, I believe, the Qyoto C#/Mono bindings.
The other disadvantage is that, while you can definitely write applications like this, in order to distribute them, you’ll need people to have:
* Ruby
* Qt (the right version)
* QtRuby
That’s fine for limited distribution, but for wide-scale it would probably be a problem. Nonetheless, this is kickass, as Qt is something like the coolest UI toolkit on the face of the planet
And just imagine… When Qt 4.4 comes out, it’ll come with WebKit integrated! 
Paul Betts said,
July 27, 2007 @ 10:06 pm
This is definitely a problem I’m aware of. My grandiose plan is to make Rake tasks that automatically package an application for all three platforms, doing “the right thing” for Win, Mac, and Linux. However, that’s a pretty far-out vision - in the interim, basically my plan is to include the Qt and QtRuby libraries statically in the .app. I’m also considering the actual main executable a stub that possibly goes out and downloads the Ruby one-click installer.
For Linux, it really isn’t a problem at all - you just set the dependencies in the DEB/RPM. Mac and Windows are the “hard” ones, especially Windows having weird compiler issues on top of the packaging issues.
Senthil Nayagam said,
July 30, 2007 @ 2:59 am
I agree possibilities are enormous for cross platform applications.
I was pretty excited to see a book on qtruby
http://pragmaticprogrammer.com/titles/ctrubyqt/index.html
but ruby qt4 gem/bindings for windows are still not available.
last message I see in the rubyforge discussion is over a year old
http://rubyforge.org/forum/message.php?msg_id=9388
the ruby version which windows generally use, one click installer or instant rails is compiled with VC++ and not mingw.
hope someone builds a mswin32 gem for us
Senthil
del.icio.us bookmarks - 2007-08-26 said,
August 27, 2007 @ 2:20 am
[…] Cross-platform UI with Qt4 and Ruby – Mac/Linux HOWTO ยป Thursday Night […]
Gabe Johnson said,
April 5, 2008 @ 12:52 pm
Hi, thanks for the post, it helped.
I am not sure if the Qt/Ruby bindings are being actively developed any longer. The most recent version (1.4.9) from http://rubyforge.org/projects/korundum/ is (as of today) ten months old. It does not compile correctly out of the box, so it can be made to work if you are patient.
Here’s how:
1. After downloading qt-ruby-1.4.9, you’ll need to also get some more recent perl code. Go here: http://websvn.kde.org/trunk/KDE/kdebindings/kalyptus/ and download the files ‘kalyptus’ and ‘kalyptusCxxToSmoke.pm’, and replace your local versions with those.
2. cmake .
3. make
It will fail at some point with an error complaining about a header file that can’t be found. Edit the c++ file (in my case it was x_14.cpp) and simply comment out the offending line. The c++ file was generated by smoke, which is done earlier in the ‘make’ process.
4. make (again)
5. sudo make install
The ruby code in this blog post works! Unfortunately, the ‘Hello world’ code I’ve seen elsewhere fails. I don’t know if this has to do with changes to the Qt API or not, since I’m a Qt nube.
Hope that helps somebody, somewhere.
Simone D. said,
April 6, 2008 @ 2:43 am
It worked for me too (thanks Gabe Johnson for your tip)!
Dilney said,
April 21, 2008 @ 2:25 pm
Thanks for the post and thanks Gabe Johnson for the tip. I finally got it working…