Tuix

A terminal UI framework for Elixir, inspired by OpenTUI.

Build declarative, component-based TUIs with a LiveView-style programming model: state lives in assigns, events arrive in callbacks, and render/1 describes the UI as a tree of boxes and text. Tuix resolves the tree with a flexbox-subset layout engine and writes only the terminal cells that changed.

defmodule Counter do
  use Tuix.App

  @impl true
  def mount(_opts, app) do
    {:ok, assign(app, count: 0)}
  end

  @impl true
  def handle_event(%Tuix.Event.Key{key: "+"}, app) do
    {:noreply, update(app, :count, &(&1 + 1))}
  end

  def handle_event(%Tuix.Event.Key{key: "q"}, app) do
    {:stop, :normal, app}
  end

  def handle_event(_event, app), do: {:noreply, app}

  @impl true
  def render(assigns) do
    box border: :rounded, title: "Counter", padding: 1, gap: 1 do
      text("Count: #{assigns.count}", fg: "#00FF00", attrs: [:bold])
      text("Press + to increment, q to quit", fg: :bright_black)
    end
  end
end

Tuix.run(Counter)

Try it: mix run examples/counter.exs

Features

• LiveView-style apps - mount/2, handle_event/2, handle_info/2, and a pure render/1 over assigns. Any Elixir message (timers, Task results, PubSub broadcasts) can drive the UI through handle_info/2.
• Declarative components - box and text are plain data constructors; conditionals and comprehensions compose naturally inside do blocks.
• Flexbox-subset layout - flex_direction, flex_grow, gap, padding, borders, fixed and percentage sizes.
• Diffed rendering - frames are cell buffers; unchanged rows are skipped with a single term comparison and only changed cells are written, as position-addressed ANSI runs.
• Unicode-aware - grapheme-based cells with correct handling of wide characters (CJK, emoji), with an ASCII fast path.
• Pure Elixir - no NIFs, no ports, no external binaries. Raw terminal mode comes from OTP itself.
• Testable without a terminal - Tuix.TestRenderer renders any app or element tree to a text snapshot or inspectable cell buffer.

Requirements

• Elixir 1.15+
• Erlang/OTP 29+

OTP 29 provides raw terminal mode (:shell.start_interactive/1), the terminfo-aware :io_ansi module used for terminal setup and capability detection, and SIGWINCH delivery for resize events.

Installation

Add tuix to your dependencies in mix.exs:

def deps do
  [
    {:tuix, "~> 0.1.0"}
  ]
end

Core concepts

Apps

A Tuix app is a module using the Tuix.App behaviour. State lives in assigns, updated with assign/2,3 and update/3. Callbacks return {:noreply, app} to continue or {:stop, reason, app} to quit. Tuix.run/2 takes over the terminal (raw mode + alternate screen), blocks until the app stops, and restores the terminal on exit - including crashes.

Rendering is event-driven: nothing is written unless state changes, and render/1 is treated as a pure function of assigns, so no-op messages cost nothing.

Components

box border: :single, flex_direction: :row, gap: 2, padding: 1 do
  text("left", fg: :cyan)

  box flex_grow: 1 do
    text("stretches to fill the remaining space")
  end

  text("right", attrs: [:bold, :underline])
end

Box props:width / height (cells, {:percent, n}, or "50%"), flex_direction (:column default, :row), flex_grow, gap, padding, border (:single, :rounded, :double), border_color, title, bg.

Text props:fg, bg, attrs (:bold, :dim, :italic, :underline, :blink, :reverse, :strikethrough). Multi-line strings render one line per row.

Colors: hex strings ("#FF8800"), RGB tuples ({255, 136, 0}), or named atoms (:red, :bright_cyan, ...).

Events

Keyboard input arrives as %Tuix.Event.Key{} with a key (a grapheme like "a" or a named atom like :up, :enter, :escape) and ctrl / alt / shift modifier flags. Terminal resizes arrive as %Tuix.Event.Resize{} and automatically reflow the layout.

Testing

test "renders the counter" do
  assert Tuix.TestRenderer.render_to_text(Counter, 14, 3, count: 42) ==
           """
           ┌────────────┐
           │Count: 42   │
           └────────────┘
           """
           |> String.trim_trailing()
end

render/4 returns the underlying Tuix.Buffer for structured assertions on individual cells and their styles.

Design notes and known trade-offs

• Full-tree re-render per state change is the LiveView-style trade-off: simple mental model, no manual invalidation. The frame diff keeps terminal writes minimal regardless.
• Resize detection uses SIGWINCH where the OTP/platform supports it (:os.set_signal/2), falling back to 250ms polling elsewhere.
• Wide-character edge case: a continuation cell changing without its head cell is not repainted. This only occurs when new content partially overlaps a wide grapheme.
• No mouse, focus, or input components yet - see the roadmap.

Roadmap

• Input, Select, and ScrollBox components with focus management
• Mouse support
• justify_content / align_items / wrapping in the layout engine
• Kitty keyboard protocol
• Animation / frame-loop rendering mode

Documentation

Documentation can be generated with ExDoc:

mix docs

Once published, the docs can be found at https://hexdocs.pm/tuix.

License

Copyright 2026 Ryan Winchester

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.