Programming language: Crystal
Tags: GUI Library    
Latest version: v0.1.0

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Crystal Bindings to Qt 5 Beta

Bindings for the Qt5 Framework using bindgen.

Platform support

System Status Qt version OOTB?
ArchLinux Works always 5.10 YES
Ubuntu 17.04 Works 5.9 YES
Ubuntu 16.04 Works 5.5 YES
MacOS Help wanted ? ?
Windows Help wanted ? ?
Other systems Help wanted ? ?

Ready-to-use Qt versions: 5.5 to 5.10

Project Goals

  • Just Works™ - Drop the dependency into a project, and use it.
  • Providing an API that feels native to Crystal
  • Focus on the GUI components (That is, QtCore, QtGui, QtWidgets)


Add this to your application's shard.yml:

    github: Papierkorb/qt5.cr
    branch: master-ready-to-use

Your users will require the Qt5 libraries on their system.

Additional development dependencies

Using your systems package manager:

  • ArchLinux pacman -S qt5-base
  • Debian apt-get install qtbase5-dev
  • Ubuntu apt-get install qtbase5-dev

Sample code

Have a look in samples/!

A short Hello World snippet looks like this:

require "qt5" # Require it!

qApp = Qt::Application.new # Create the application

# Display something on the screen
label = Qt::Label.new "Hello from Crystal/Qt!"

Qt::Application.exec # And run it!


A note on Qt's license

A common misconception is that you have to pay for Qt to use it in closed-source applications.

This project assumes you'll link to Qt dynamically. In this case, you can use Qt free of charge including for closed-source, commercial applications under the terms of the LGPL.

You can build closed-source applications using Crystal, this shard, and Qt for free.

Note: This section is to combat this misconception, the authors of qt5.cr are in no way responsible to check if the same terms apply in your jurisdiction.

Generating the bindings

If you want to work on qt5.cr itself, or have a custom build of Qt you want to use, you'll have to generate the bindings yourself.

These steps can be followed from a project using qt5.cr, or from within qt5.cr itself. For the latter, just check out the master branch instead of changing a shard.yml.

Important: For this you'll also have to meet the dependencies of bindgen.

Naming scheme

As qt5.cr supports many different versions of Qt on different platforms, generated bindings follow a naming scheme. The scheme is as follows:

  • KERNEL-LIB_C-ARCH-qtVERSION, e.g. linux-gnu-x86_64-qt5.10
  • KERNEL is the OS kernel, e.g. linux, darwin, windows
  • LIB_C is the lib C name, e.g. gnu, musl, win32
  • ARCH is the architecture, e.g. i686, x86_64, arm
  • VERSION is the Qt version, e.g. 5.5, 5.6, ...

The naming scheme is not strictly enforced. However, it should always end with -qtVERSION!

Generating all binding versions

The master-ready-to-use branch is built using this method:

  1. Change into the qt5.cr directory
  2. If you want to change which bindings to generate, edit support/generate_bindings.cr
  3. Run crystal support/generate_bindings.cr

The script will automatically download, unpack, build and generate all configured versions of Qt. It'll store the Qt5 versions in a directory called download_cache/. Subsequent invocations of that script will use these cached assets. The first run may take a long time.

Generating a specific binding version

  1. Use the master branch of qt5.cr in your shard.yml
  2. Run crystal deps to download dependencies
  3. Decide which version of Qt to use, and build the scheme (See above)
  4. Export the binding scheme: export BINDING_PLATFORM=linux-gnu-x86_64-qt5.10
  5. If you're not using your systems Qt: export QMAKE=/path/to/qmake
  6. Run bindgen: lib/bindgen/tool.sh qt.yml --stats
  7. Verify: crystal spec

Future things to do

  • Forwarding qHash() of wrapped types (to Object#hash)
  • Integration with LibEvent: Right now, Qt blocks the whole thread.
  • The rest of the billion Qt classes of interest
  • Everything in the to be done category
  • Integration for the Qt Designer UI designer
  • Integration for Qt Linguist
    • Localization/Translation for your applications!
  • UI test library, with adapter for spec
    • Also, actual tests - Let's catch whacko bugs right in the CI!
  • Automated copy (and adaption) of the Qt documentation, for easy Crystal-specific docs
    • The Qt Docs license should allow this if done correctly


  1. Talk to Papierkorb in #crystal-lang about what you're gonna do.
  2. You got the go-ahead? The project's in an early state: Things may change without notice under you.
  3. Then do the rest, PR and all. You know the drill.


The Qt bindings, including the generated and manually-written parts, are subject to the MPL-2 license. You can find a copy attached of the full license text in the LICENSE file.

This project claims no copyright on the Qt framework or of any of its trademarks, source, or any other assets.

Questions? Contact Papierkorb.


  • Papierkorb Stefan Merettig - creator, maintainer

*Note that all licence references and agreements mentioned in the qt5.cr README section above are relevant to that project's source code only.