Context

R3BL TUI library & suite of apps focused on developer productivity

We are working on building command line apps in Rust which have rich text user interfaces (TUI). We want to lean into the terminal as a place of productivity, and build all kinds of awesome apps for it.

  1. 🔮 Instead of just building one app, we are building a library to enable any kind of rich TUI development w/ a twist: taking concepts that work really well for the frontend mobile and web development world and re-imagining them for TUI & Rust.

  2. 🌎 We are building apps to enhance developer productivity & workflows.

r3bl_tui crate

Text User Interface library for Rust

You can build fully async TUI (text user interface) apps with a modern API that brings the best of the web frontend development ideas to TUI apps written in Rust:

  1. Reactive & unidirectional data flow architecture from frontend web development (React, Redux).
  2. Responsive design w/ CSS, flexbox like concepts.
  3. Declarative style of expressing styling and layouts.

And since this is using Rust and Tokio you get the advantages of concurrency and parallelism built-in. No more blocking the main thread for user input, for async middleware, or even rendering 🎉.

This framework is loosely coupled and strongly coherent meaning that you can pick and choose whatever pieces you would like to use w/out having the cognitive load of having to grok all the things in the codebase. Its more like a collection of mostly independent modules that work well w/ each other, but know very little about each other.

Here are some framework highlights:

Examples to get you started

Here's a video of the demo in action:

https://user-images.githubusercontent.com/2966499/200138653-c0cf925f-2c91-4908-9ed5-1e216b5dd547.webm

  1. You can run cargo run --example demo in the tui/examples folder to see a demo of the library in action and play with it. The examples cover the entire surface area of the TUI API. You can also take a look at the tests in the source as well tui/src/.

  2. The design docs and architecture diagrams in the docs folder are a good place to start to get a feel for the architecture of the framework. You can get a mental model of how everything fits and what the TUI lifecycle is.

  3. Additionally the r3blrsutils_core has the tui_core module which contains dependencies that are used by the tui module. They include:

    1. ANSI text support.
    2. Core dimensions and units that are used for positioning and sizing.
    3. Grapheme cluster segment and unicode support (emoji support).
    4. Lolcat support.
    5. CSS like styling support.

Life of an input event

There is a clear separation of concerns in this module. To illustrate what goes where, and how things work let's look at an example that puts the main event loop front and center & deals w/ how the system handles an input event (key press or mouse).

text 🧍⌨️🖱️ input → [TerminalWindow] event ↑ ↓ [ComponentRegistry] creates ┊ [App] ───────────■ [Component]s at 1st render ┊ │ ┊ │ ┌──────■ id=1 has focus ┊ │ │ ┊ ├→ [Component] id=1 ───┐ ┊ ├→ [Component] id=2 │ ┊ └→ [Component] id=3 │ default │ handler ←───────────────────────┘

Let's trace the journey through the diagram when an input even is generated by the user (eg: a key press, or mouse event). When the app is started via cargo run it sets up a main loop, and lays out all the 3 components, sizes, positions, and then paints them. Then it asynchronously listens for input events (no threads are blocked). When the user types something, this input is processed by the main loop of [TerminalWindow].

  1. The [Component] that is in [FlexBox] w/ id=1 currently has focus.
  2. When an input event comes in from the user (key press or mouse input) it is routed to the [App] first, before [TerminalWindow] looks at the event.
  3. The specificity of the event handler in [App] is higher than the default input handler in [TerminalWindow]. Further, the specificity of the [Component] that currently has focus is the highest. In other words, the input event gets routed by the [App] to the [Component] that currently has focus ([Component] id=1 in our example).
  4. Since it is not guaranteed that some [Component] will have focus, this input event can then be handled by [App], and if not, then by [TerminalWindow]'s default handler. If the default handler doesn't process it, then it is simply ignored.
  5. In this journey, as the input event is moved between all these different entities, each entity decides whether it wants to handle the input event or not. If it does, then it returns an enum indicating that the event has been consumed, else, it returns an enum that indicates the event should be propagated.

Now that we have seen this whirlwind overview of the life of an input event, let's look at the details in each of the sections below.

Here's an architecture diagram that will be useful to keep in mind as we go through the details of the following sections:

The window

The main building blocks of a TUI app are:

  1. [TerminalWindow] - You can think of this as the main "window" of the app. All the content of your app is painted inside of this "window". And the "window" conceptually maps to the screen that is contained inside your terminal emulator program (eg: tilix, Terminal.app, etc). Your TUI app will end up taking up 100% of the screen space of this terminal emulator. It will also enter raw mode, and paint to an alternate screen buffer, leaving your original scroll back buffer and history intact. When you exit this TUI app, it will return your terminal to where you'd left off. You don't write this code, this is something that you use.
  2. [App] - This is where you write your code. You pass in a [App] to the [TerminalWindow] to bootstrap your TUI app. You can just use [App] to build your app, if it is a simple one & you don't really need any sophisticated layout or styling. But if you want layout and styling, now we have to deal with [FlexBox], [Component], and [crate::Style].

Layout and styling

Inside of your [App] if you want to use flexbox like layout and CSS like styling you can think of composing your code in the following way:

  1. [App] is like a box or container. You can attach styles and an id here. The id has to be unique, and you can reference as many styles as you want from your stylesheet. Yes, cascading styles are supported! 👏 You can put boxes inside of boxes. You can make a container box and inside of that you can add other boxes (you can give them a direction and even relative sizing out of 100%).
  2. As you approach the "leaf" nodes of your layout, you will find [Component] trait objects. These are black boxes which are sized, positioned, and painted relative to their parent box. They get to handle input events and render [RenderOp]s into a [RenderPipeline]. This is kind of like virtual DOM in React. This queue of commands is collected from all the components and ultimately painted to the screen, for each render! You can also use Redux to maintain your app's state, and dispatch actions to the store, and even have async middleware!

Component, ComponentRegistry, focus management, and event routing

Typically your [App] will look like this:

```rust /// Async trait object that implements the [App] trait.

[derive(Default)]

pub struct AppWithLayout { pub componentregistry: ComponentRegistry, pub hasfocus: HasFocus, } ```

As we look at [Component] & [App] more closely we will find a curious thing [ComponentRegistry] (that is managed by the [App]). The reason this exists is for input event routing. The input events are routed to the [Component] that currently has focus.

The [HasFocus] struct takes care of this. This provides 2 things:

  1. It holds an id of a [FlexBox] / [Component] that has focus.
  2. It also holds a map that holds a [crate::Position] for each id. This is used to represent a cursor (whatever that means to your app & component). This cursor is maintained for each id. This allows a separate cursor for each [Component] that has focus. This is needed to build apps like editors and viewers that maintains a cursor position between focus switches.

Another thing to keep in mind is that the [App] and [TerminalWindow] is persistent between re-renders. The Redux store is also persistent between re-renders.

Input event specificity

[TerminalWindow] gives [Component] first dibs when it comes to handling input events. If it punts handling this event, it will be handled by the default input event handler. And if nothing there matches this event, then it is simply dropped.

Redux for state management

If you use Redux for state management, then you will create a [crate::redux] [crate::Store] that is passed into the [TerminalWindow]. Here's an example of this.

```rust use crossterm::event::; use r3bl_rs_utils::; use super::*;

const DEBUG: bool = true;

pub async fn runapp() -> CommonResult<()> { throws!({ if DEBUG { trytosetloglevel(log::LevelFilter::Trace)?; } else { trytosetlog_level(log::LevelFilter::Off)?; }

// Create store.
let store = create_store().await;

// Create an App (renders & responds to user input).
let shared_app = AppWithLayout::new_shared();

// Exit if these keys are pressed.
let exit_keys: Vec<KeyEvent> = vec![KeyEvent {
  code: KeyCode::Char('q'),
  modifiers: KeyModifiers::CONTROL,
}];

// Create a window.
TerminalWindow::main_event_loop(store, shared_app, exit_keys).await?

}); }

async fn createstore() -> Store { let mut store: Store = Store::default(); store.addreducer(AppReducer::new()).await; store } ```

Grapheme support

Unicode is supported (to an extent). There are some caveats. The [crate::UnicodeStringExt] trait has lots of great information on this graphemes and what is supported and what is not.

Lolcat support

An implementation of [crate::lolcat::cat] w/ a color wheel is provided.

Other crates that depend on this

This crate is a dependency of the following crates:

  1. r3bl_rs_utils crates (the "main" library)

Issues, comments, feedback, and PRs

Please report any issues to the issue tracker. And if you have any feature requests, feel free to add them there too 👍.