tui-scrollbar

Smooth, fractional scrollbars for Ratatui. Part of the tui-widgets suite by Joshka.

GitHub Repository · API Docs · Examples · Changelog · Contributing · Crate source

Use this crate when you want scrollbars that communicate position and size more precisely than full-cell glyphs. The widget renders into a Buffer for a given Rect and stays reusable by implementing Widget for &ScrollBar.

Feature highlights

• Fractional thumbs: render 1/8th-cell steps for clearer position/size feedback.
• Arrow endcaps: optional start/end arrows with click-to-step support.
• Backend-agnostic input: handle pointer + wheel events without tying to a backend.
• Stateless rendering: render via Widget for &ScrollBar with external state.
• Metrics-first: [ScrollMetrics] exposes pure geometry for testing and hit testing.

Why not Ratatui's scrollbar?

Ratatui's built-in scrollbar favors simple full-cell glyphs and a stateful widget workflow. This crate chooses fractional glyphs for more precise thumbs, keeps rendering stateless, and exposes a small interaction API plus pure metrics so apps can control behavior explicitly.

Installation

cargo add tui-scrollbar

Quick start

This example renders a vertical [ScrollBar] into a Buffer using a fixed track size and offset. Use it as a minimal template when you just need a thumb and track on screen. If you prefer named arguments, use [ScrollLengths].

use ratatui_core::buffer::Buffer;
use ratatui_core::layout::Rect;
use ratatui_core::widgets::Widget;
use tui_scrollbar::{ScrollBar, ScrollBarArrows, ScrollLengths};

let area = Rect::new(0, 0, 1, 6);
let lengths = ScrollLengths {
    content_len: 120,
    viewport_len: 30,
};
let scrollbar = ScrollBar::vertical(lengths)
    .arrows(ScrollBarArrows::Both)
    .offset(45);

let mut buffer = Buffer::empty(area);
scrollbar.render(area, &mut buffer);

Conceptual overview

The scrollbar works in three pieces:

1. Your app owns content_len, viewport_len, and offset (lengths along the scroll axis).
2. [ScrollMetrics] converts those values into a thumb position and size.
3. [ScrollBar] renders the track + thumb using fractional glyphs.

Most apps update offset in response to input events and re-render each frame.

Units and subcell conversions

content_len, viewport_len, and offset are measured in logical units along the scroll axis. For many apps, those units are items or lines. The ratio between viewport_len and content_len is what matters, so any consistent unit works.

Zero lengths are treated as 1.

Layout integration

This example shows how to reserve a column for a vertical [ScrollBar] alongside your content. Use the same pattern for a horizontal [ScrollBar] by splitting rows instead of columns.

use ratatui_core::buffer::Buffer;
use ratatui_core::layout::{Constraint, Layout, Rect};
use ratatui_core::widgets::Widget;
use tui_scrollbar::{ScrollBar, ScrollLengths};

let area = Rect::new(0, 0, 12, 6);
let [content_area, bar_area] = area.layout(&Layout::horizontal([
    Constraint::Fill(1),
    Constraint::Length(1),
]));

let lengths = ScrollLengths {
    content_len: 400,
    viewport_len: 80,
};
let scrollbar = ScrollBar::vertical(lengths).offset(0);

let mut buffer = Buffer::empty(area);
scrollbar.render(bar_area, &mut buffer);

Interaction loop

This pattern assumes you have enabled mouse capture in your terminal backend and have the scrollbar Rect (bar_area) from your layout each frame. Keep a [ScrollBarInteraction] in your app state so drag operations persist across draws. Mouse events are handled via [ScrollBar::handle_mouse_event], which returns a [ScrollCommand] to apply.

use ratatui_core::layout::Rect;
use tui_scrollbar::{ScrollBar, ScrollBarInteraction, ScrollCommand, ScrollLengths};

let bar_area = Rect::new(0, 0, 1, 10);
let lengths = ScrollLengths {
    content_len: 400,
    viewport_len: 80,
};
let scrollbar = ScrollBar::vertical(lengths).offset(0);
let mut interaction = ScrollBarInteraction::new();
let mut offset = 0;

if let Event::Mouse(event) = event::read()? {
    if let Some(ScrollCommand::SetOffset(next)) =
        scrollbar.handle_mouse_event(bar_area, event, &mut interaction)
    {
        offset = next;
    }
}

Metrics-first workflow

This example shows how to compute thumb geometry without rendering via [ScrollMetrics]. It's useful for testing, hit testing, or when you want to inspect thumb sizing directly.

use tui_scrollbar::{ScrollLengths, ScrollMetrics, SUBCELL};

let track_cells = 12;
let viewport_len = track_cells * SUBCELL;
let content_len = viewport_len * 6;
let lengths = ScrollLengths {
    content_len,
    viewport_len,
};
let metrics = ScrollMetrics::new(lengths, 0, track_cells as u16);
assert!(metrics.thumb_len() >= SUBCELL);

Glyph selection

The default glyphs include Symbols for Legacy Computing so the thumb can render upper/right partial fills that are missing from the standard block set. Use [GlyphSet] when you want to switch to a glyph set that avoids legacy symbols.

use tui_scrollbar::{GlyphSet, ScrollBar, ScrollLengths};

let lengths = ScrollLengths {
    content_len: 10,
    viewport_len: 5,
};
let scrollbar = ScrollBar::vertical(lengths).glyph_set(GlyphSet::unicode());

API map

Widgets

• [ScrollBar]: renders vertical or horizontal scrollbars with fractional thumbs.

Supporting types

• [ScrollBarInteraction]: drag capture state for pointer interaction.
• [ScrollMetrics]: pure math for thumb sizing and hit testing.
• [GlyphSet]: glyph selection for track and thumb rendering.
• [ScrollBarArrows]: arrow endcap configuration.

Enums and events

• [ScrollBarOrientation], [ScrollBarArrows], [TrackClickBehavior]
• [ScrollEvent], [ScrollCommand]
• [PointerEvent], [PointerEventKind], [PointerButton]
• [ScrollWheel], [ScrollAxis]

Features

• crossterm: enables the handle_mouse_event adapter for crossterm mouse events.

Important

• Zero lengths are treated as 1.
• Arrow endcaps are disabled by default; configure them with [ScrollBarArrows].
• The default [GlyphSet] hides the track using spaces; use [GlyphSet::box_drawing] or [GlyphSet::unicode] for a visible track.
• The default glyphs use Symbols for Legacy Computing for missing upper/right eighth blocks. Use [GlyphSet::unicode] if you need only standard Unicode block elements.

See also

• tui-scrollbar examples
• scrollbar_mouse example
• scrollbar example
• Widget
• Ratatui

More widgets

For the full suite of widgets, see tui-widgets.

License

Copyright (c) Josh McKinney

This project is licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

See CONTRIBUTING.md.