Crate ratatui

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ratatui is a library used to build rich terminal users interfaces and dashboards.

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Adding ratatui as a dependency

Add the following to your Cargo.toml:

[dependencies]
crossterm = "0.26"
ratatui = "0.20"

The crate is using the crossterm backend by default that works on most platforms. But if for example you want to use the termion backend instead. This can be done by changing your dependencies specification to the following:

[dependencies]
termion = "1.5"
ratatui = { version = "0.20", default-features = false, features = ['termion'] }

The same logic applies for all other available backends.

Features

Widgets which add dependencies are gated behind feature flags to prevent unused transitive dependencies. The available features are:

Creating a Terminal

Every application using ratatui should start by instantiating a Terminal. It is a light abstraction over available backends that provides basic functionalities such as clearing the screen, hiding the cursor, etc.

use std::io;
use ratatui::{backend::CrosstermBackend, Terminal};

fn main() -> Result<(), io::Error> {
    let stdout = io::stdout();
    let backend = CrosstermBackend::new(stdout);
    let mut terminal = Terminal::new(backend)?;
    Ok(())
}

If you had previously chosen termion as a backend, the terminal can be created in a similar way:

ⓘ
use std::io;
use ratatui::{backend::TermionBackend, Terminal};
use termion::raw::IntoRawMode;

fn main() -> Result<(), io::Error> {
    let stdout = io::stdout().into_raw_mode()?;
    let backend = TermionBackend::new(stdout);
    let mut terminal = Terminal::new(backend)?;
    Ok(())
}

You may also refer to the examples to find out how to create a Terminal for each available backend.

Building a User Interface (UI)

Every component of your interface will be implementing the Widget trait. The library comes with a predefined set of widgets that should meet most of your use cases. You are also free to implement your own.

Each widget follows a builder pattern API providing a default configuration along with methods to customize them. The widget is then rendered using Frame::render_widget which takes your widget instance and an area to draw to.

The following example renders a block of the size of the terminal:

use std::{io, thread, time::Duration};
use ratatui::{
    backend::CrosstermBackend,
    widgets::{Block, Borders},
    Terminal
};
use crossterm::{
    event::{self, DisableMouseCapture, EnableMouseCapture},
    execute,
    terminal::{disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen},
};

fn main() -> Result<(), io::Error> {
    // setup terminal
    enable_raw_mode()?;
    let mut stdout = io::stdout();
    execute!(stdout, EnterAlternateScreen, EnableMouseCapture)?;
    let backend = CrosstermBackend::new(stdout);
    let mut terminal = Terminal::new(backend)?;

    terminal.draw(|f| {
        let size = f.size();
        let block = Block::default()
            .title("Block")
            .borders(Borders::ALL);
        f.render_widget(block, size);
    })?;

    // Start a thread to discard any input events. Without handling events, the
    // stdin buffer will fill up, and be read into the shell when the program exits.
    thread::spawn(|| loop {
        event::read();
    });

    thread::sleep(Duration::from_millis(5000));

    // restore terminal
    disable_raw_mode()?;
    execute!(
        terminal.backend_mut(),
        LeaveAlternateScreen,
        DisableMouseCapture
    )?;
    terminal.show_cursor()?;

    Ok(())
}

Layout

The library comes with a basic yet useful layout management object called Layout. As you may see below and in the examples, the library makes heavy use of the builder pattern to provide full customization. And Layout is no exception:

use ratatui::{
    backend::Backend,
    layout::{Constraint, Direction, Layout},
    widgets::{Block, Borders},
    Frame,
};
fn ui<B: Backend>(f: &mut Frame<B>) {
   let chunks = Layout::default()
        .direction(Direction::Vertical)
        .margin(1)
        .constraints(
            [
                Constraint::Percentage(10),
                Constraint::Percentage(80),
                Constraint::Percentage(10)
            ].as_ref()
        )
        .split(f.size());
    let block = Block::default()
         .title("Block")
         .borders(Borders::ALL);
    f.render_widget(block, chunks[0]);
    let block = Block::default()
         .title("Block 2")
         .borders(Borders::ALL);
    f.render_widget(block, chunks[1]);
}

This let you describe responsive terminal UI by nesting layouts. You should note that by default the computed layout tries to fill the available space completely. So if for any reason you might need a blank space somewhere, try to pass an additional constraint and don’t use the corresponding area.

Re-exports

Modules

Macros

  • assert_buffer_eq
    Assert that two buffers are equal by comparing their areas and content.
  • border
    Macro that constructs and returns a Borders object from TOP, BOTTOM, LEFT, RIGHT, NONE, and ALL. Internally it creates an empty Borders object and then inserts each bit flag specified into it using Borders::insert().