build Gem Version glimmer-dsl-libui

:radio_button: libui - a portable GUI library - for Ruby


gem install libui
  • The gem package contains the official release of the libui shared library versions 4.1 for Windows, Mac, and Linux.
    • Namely libui.dll, libui.dylib, and (only 1.8MB in total).
  • No dependency
    • The libui gem uses the standard Ruby library Fiddle to call C functions.
Windows Mac Linux


  • If you are using the 32-bit (x86) version of Ruby, you need to download the 32-bit (x86) native dll. See Development.
  • On Windows, libui may not work due to missing DLLs. In that case, you need to install Visual C++ Redistributable. See (#48)


require 'libui'

UI = LibUI


main_window = UI.new_window('hello world', 200, 100, 1)

button = UI.new_button('Button')

UI.button_on_clicked(button) do
  UI.msg_box(main_window, 'Information', 'You clicked the button')

UI.window_on_closing(main_window) do
  puts 'Bye Bye'

UI.window_set_child(main_window, button)


See examples directory.

General Rules

Compared to original libui written in C,

  • The method names are snake_case.
  • If the last argument is nil, it can be omitted.
  • You can pass a block as a callback.
    • The block will be converted to a Proc object and added to the last argument.
    • Even in that case, it is possible to omit the last argument when nil.

You can use the documentation for libui's Go bindings as a reference.

DSLs for LibUI

LibUI is not object-oriented, but provides high portability with minimal implementation. If you want to write in an object-oriented way, please use the following DSLs built on top of LibUI.

How to use fiddle pointers?

require 'libui'
UI = LibUI

Convert a pointer to a string.

label = UI.new_label("Ruby")
p pointer = UI.label_text(label) # #<Fiddle::Pointer>
p pointer.to_s # Ruby

If you need to use C structs, you can do the following.

font_button = UI.new_font_button

# Allocate memory 
font_descriptor = UI::FFI::FontDescriptor.malloc = Fiddle::RUBY_FREE
# font_descriptor = UI::FFI::FontDescriptor.malloc(Fiddle::RUBY_FREE) # fiddle 1.0.1 or higher

UI.font_button_on_changed(font_button) do
  UI.font_button_font(font_button, font_descriptor)
  p family:  font_descriptor.Family.to_s,
    size:    font_descriptor.Size,
    weight:  font_descriptor.Weight,
    italic:  font_descriptor.Italic,
    stretch: font_descriptor.Stretch
  • Callbacks
    • In Ruby/Fiddle, a C callback function is written as an object of Fiddle::Closure::BlockCaller or Fiddle::Closure. In this case, you need to be careful about Ruby's garbage collection. If the function object is collected, memory will be freed and a segmentation violation will occur when the callback is invoked.
# to a local variable to prevent it from being collected by GC.
handler.MouseEvent   = (c1 =, [0]) {})
handler.MouseCrossed = (c2 =, [0]) {})
handler.DragBroken   = (c3 =, [0]) {})

How to create an executable (.exe) on Windows

OCRA (One-Click Ruby Application) builds Windows executables from Ruby source code.

In order to build a exe with Ocra, include 3 DLLs from ruby_builtin_dlls folder:

ocra examples/control_gallery.rb        ^
  --dll ruby_builtin_dlls/libssp-0.dll  ^
  --dll ruby_builtin_dlls/libgmp-10.dll ^
  --dll ruby_builtin_dlls/libffi-7.dll  ^
  --gem-all=fiddle                      ^

Add additional options below if necessary.

  --window                              ^
  --add-all-core                        ^
  --chdir-first                         ^
  --icon assets\app.ico                 ^
  --verbose                             ^
  --output out\gallery.exe


git clone
cd libui
bundle install
bundle exec rake vendor:default # download shared libraries for all platforms
bundle exec rake test

You can use the following rake tasks to download the shared library required for your platform.

rake -T

rake vendor:default      # Downlaod [linux_x64, mac_arm, windows_x64] to vendor directory
rake vendor:linux_x64    # Download for Linux to vendor directory
rake vendor:linux_x86    # Download for Linux to vendor directory
rake vendor:mac_arm      # Download libui.dylib for Mac to vendor directory (universal binary)
rake vendor:mac_x64      # Download libui.dylib for Mac to vendor directory
rake vendor:windows_x64  # Download libui.dll for Windows to vendor directory
rake vendor:windows_x86  # Download libui.dll for Windows to vendor directory

For example, If you are using a 32-bit (x86) version of Ruby on Windows, type rake vendor:windows_x86.

Or Set environment variable LIBUIDIR to specify the path to the shared library.


Would you like to add your commits to libui?

  • Please feel free to send us your pull requests.
    • Small corrections, such as typo fixes, are appreciated.
  • Did you find any bugs? Enter in the issues section!

I have seen many OSS projects abandoned. The main reason is that no one has the right to commit to the original repository, except the founder. Do you need commit rights to my repository? Do you want to get admin rights and take over the project? If so, please feel free to contact me @kojix2.


This project is inspired by libui-ruby.

While libui-ruby uses Ruby-FFI, this gem uses Fiddle.


MIT License.