Shoes, worn over libui.

Clogs runs Shoes programs on plain CRuby. No browser engine, no JVM — just libui, a small native widget library that ships as a prebuilt shared object for Linux, macOS and Windows.

require "clogs"

Shoes.app(title: "Hello", width: 400, height: 200) do
  para "Hello, ", strong("Shoes"), "!", size: :title
  button("Push me") { @note.replace "Aha! Clicked." }
  @note = para "Nothing pushed so far"
end

gem install clogs
clogs hello.rb

clogs is a small stand-in for Shoes 3's own shoes command: it requires clogs for you and runs the program you name. ruby hello.rb (with a top-level require "clogs" as above) works exactly the same way.

The Shoes API itself comes from Lacci, the display-independent half of Scarpe. Lacci owns the DSL and the drawable tree; Clogs is a Lacci display service and owns the pixels.

your Shoes program
        |
      Lacci                the Shoes DSL, drawable tree, events
        |
      Clogs                layout, painting, widgets, input
        |
libui/FOX/wx/Qt/GTK3/NAppGUI   one native window, one canvas

The bottom layer is swappable. libui is the default because it is the only one that installs without a compiler; CLOGS_BACKEND=fox runs the same Clogs on FXRuby, CLOGS_BACKEND=wx on wxRuby3, CLOGS_BACKEND=qt on Qt 6 through a C shim in ext/qt -- Ruby has no maintained Qt binding, so that backend brings its own -- CLOGS_BACKEND=gtk3 on ruby-gnome, and CLOGS_BACKEND=nappgui on NAppGUI through a second C shim in ext/nappgui, for the same reason and one more: its osmain macro wants to define main(). All six pass the same 11 of 12 Shoes samples. All five alternatives can blit a bitmap, which libui cannot, making an artwork-heavy frame 10x to 150x cheaper; wx, Qt, gtk3 and NAppGUI match libui's drawing exactly, while FOX trades antialiasing and alpha for more speed still.

gtk3 is the one to read first: on Linux libui is GTK3 and Cairo, one C wrapper down, so the difference between those two columns is what the wrapper costs rather than what the toolkit can do. The measurements, the trade-offs and rake compare are in docs/backends.md.

You can also select it explicitly, which is useful when the same program should run under Scarpe's webview backend too:

SCARPE_DISPLAY_SERVICE=clogs ruby my_app.rb

Clogs paints the entire Shoes document into a single libui canvas, including the widgets. That is not a shortcut: libui has no way to place a native control at an arbitrary position, and Shoes needs exactly that. The trade-offs — and a tested feature-by-feature matrix — are in docs/libui_shoes_coverage.md.

The short version: layout, text, links, art drawables, images, widgets, events, animation and dialogs all work. Video, sound, blur and multiple windows do not.

cd clogs
bundle install
rake test                                  # unit tests plus real windowed runs
ruby -Ilib examples/kitchen_sink.rb        # see it

The tests open real windows, so on a headless machine run them under Xvfb:

xvfb-run -a rake test

Two environment variables make Shoes apps scriptable, which is how Clogs tests itself and how you can screenshot an app from CI:

CLOGS_EXIT_AFTER_MS=800 CLOGS_SCREENSHOT=shot.png ruby -Ilib examples/kitchen_sink.rb

MIT.