Crate ratatui_image

Expand description

§Image widgets with multiple graphics protocol backends for ratatui

ratatui is an immediate-mode TUI library. ratatui-image tackles 3 general problems when rendering images with an immediate-mode TUI:

Query the terminal for available graphics protocols

Some terminals may implement one or more graphics protocols, such as Sixels, or the iTerm2 or Kitty graphics protocols. Guess by env vars. If that fails, query the terminal with some control sequences. Fallback to “halfblocks” which uses some unicode half-block characters with fore- and background colors.

Query the terminal for the font-size in pixels.

If there is an actual graphics protocol available, it is necessary to know the font-size to be able to map the image pixels to character cell area. Query the terminal with some control sequences for either the font-size directly, or the window-size in pixels and derive the font-size together with row/column count.

Render the image by the means of the guessed protocol.

Some protocols, like Sixels, are essentially “immediate-mode”, but we still need to avoid the TUI from overwriting the image area, even with blank characters. Other protocols, like Kitty, are essentially stateful, but at least provide a way to re-render an image that has been loaded, at a different or same position. Since we have the font-size in pixels, we can precisely map the characters/cells/rows-columns that will be covered by the image and skip drawing over the image.

§Quick start

use ratatui::{backend::TestBackend, Terminal, Frame};
use ratatui_image::{picker::Picker, StatefulImage, protocol::StatefulProtocol};

struct App {
    // We need to hold the render state.
    image: StatefulProtocol,
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let backend = TestBackend::new(80, 30);
    let mut terminal = Terminal::new(backend)?;

    // Should use Picker::from_query_stdio() to get the font size and protocol,
    // but we can't put that here because that would break doctests!
    let mut picker = Picker::from_fontsize((8, 12));

    // Load an image with the image crate.
    let dyn_img = image::ImageReader::open("./assets/Ada.png")?.decode()?;

    // Create the Protocol which will be used by the widget.
    let image = picker.new_resize_protocol(dyn_img);

    let mut app = App { image };

    // This would be your typical `loop {` in a real app:
    terminal.draw(|f| ui(f, &mut app))?;
    // It is recommended to handle the encoding result
    app.image.last_encoding_result().unwrap()?;
    Ok(())
}

fn ui(f: &mut Frame<'_>, app: &mut App) {
    // The image widget.
    let image = StatefulImage::default();
    // Render with the protocol state.
    f.render_stateful_widget(image, f.area(), &mut app.image);
}

The picker::Picker helper is there to do all this font-size and graphics-protocol guessing, and also to map character-cell-size to pixel size so that we can e.g. “fit” an image inside a desired columns+rows bound, and so on.

The Image widget has a fixed size in rows/columns. If the image pixel size exceeds the pixel area of the rows/columns, the image is scaled down proportionally to “fit” once. If the actual rendering area is smaller than the initial rows/columns, it is simply not rendered at all. The big upside is that this widget is stateless (in terms of ratatui, i.e. immediate-mode), and thus can never block the rendering thread/task. A lot of ratatui apps only use stateless widgets, so this factor is also important when chosing.
The StatefulImage widget adapts to its render area at render-time. It can be set to fit, crop, or scale to the available render area. This means the widget must be stateful, i.e. use render_stateful_widget which takes a mutable state parameter. The resizing and encoding is blocking, and since it happens at render-time it is a good idea to offload that to another thread or async task, if the UI must be responsive (see examples/thread.rs and examples/tokio.rs).

§Examples

examples/demo.rs is a fully fledged demo.
examples/thread.rs shows how to offload resize and encoding to another thread, to avoid blocking the UI thread.
examples/tokio.rs same as thread.rs but with tokio.

The lib also includes a binary that renders an image file, but it is focused on testing.

§Features

crossterm or termion should match your ratatui backend. termwiz is available, but not working correctly with ratatui-image.
serde for #[derive]s on picker::ProtocolType for convenience, because it might be useful to save it in some user configuration.
image-defaults (default) just enables image/defaults (image has default-features = false). To only support a selection of image formats and cut down dependencies, disable this feature, add image to your crate, and enable its features/formats as desired. See https://doc.rust-lang.org/cargo/reference/features.html#feature-unification/.
tokio whether to use tokio’s UnboundedSender in ThreadProtocol

Modules§

errors
picker: Helper module to build a protocol, and swap protocols at runtime
protocol: Protocol backends for the widgets
thread: Widget that separates resize+encode from rendering. This allows for rendering to be non-blocking, offloading resize+encode into another thread. See examples/async.rs for how to setup the threads and channels. At least one worker thread for resize+encode is required, the example shows how to combine the needs-resize-polling with other terminal events into one event loop.

Structs§

CropOptions: Specifies which sides to be clipped when cropping an image.
Image: Fixed size image widget that uses Protocol.
StatefulImage: Resizeable image widget that uses a protocol::StatefulProtocol state.

Enums§

FilterType: Available Sampling Filters.
Resize: Resize method

Traits§

ResizeEncodeRender

Type Aliases§

FontSize: The terminal’s font size in (width, height)