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#963 in GUI

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MIT license

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RAUI Crates.ioDocs.rs


RAUI is a renderer agnostic UI system that is heavily inspired by React's declarative UI composition and the UE4 Slate widget components system.

🗣 Pronunciation: RAUI is pronounced like "ra" ( the Egyptian god ) + "oui" (french for "yes" ) — Audio Example.

The main idea behind RAUI architecture is to treat UI as another data source that you transform into your target renderable data format used by your rendering engine of choice.



Application is the central point of user interest. It performs whole UI processing logic. There you apply widget tree that wil be processed, send messages from host application to widgets and receive signals sent from widgets to host application.

// Coords mapping tell RAUI renderers how to convert coordinates
// between virtual-space and ui-space.
let mapping = CoordsMapping::new(Rect {
    left: 0.0,
    right: 1024.0,
    top: 0.0,
    bottom: 576.0,

// Application is UI host.
let mut application = Application::default();
// we use setup functions to register component and props mappings for serialization.
// we can also register them at any time one by one.
application.register_component("app", FnWidget::pointer(app));

// Widget tree is simply a set of nested widget nodes, usually made with special macros.
let tree = widget! {
    (app {
        // <named slot name> = ( <widget to put in a slot> )
        title = (title_bar: {"Hello".to_owned()})
        content = (vertical_box [
            (#{"hi"} button: {"Say hi!".to_owned()})
            (#{"exit"} button: {"Close".to_owned()})

// some dummy widget tree renderer.
// it reads widget unit tree and transforms it into target format.
let mut renderer = HtmlRenderer::default();

// `apply()` sets new widget tree.

// `render()` calls renderer to perform transformations on processed application widget tree.
if let Ok(output) = application.render(&mapping, &mut renderer) {
    println!("* OUTPUT:\n{}", output);

// by default application won't process widget tree if nothing was changed.
// "change" is either any widget state change, or new message sent to any widget (messages
// can be sent from application host, for example a mouse click, or from another widget).
if let Ok(output) = application.render(&mapping, &mut renderer) {
    println!("* OUTPUT:\n{}", output);


Widgets are divided into three categories:

  • WidgetNode - used as source UI trees (variant that can be either a component, unit or none)
  widget! {
      (app {
          // <named slot name> = ( <widget to put in a slot> )
          title = (title_bar: {"Hello".to_owned()})
          content = (vertical_box [
              (#{"hi"} button: {"Say hi!".to_owned()})
              (#{"exit"} button: {"Close".to_owned()})
  • WidgetComponent - you can think of them as Virtual DOM nodes, they store:
    • pointer to component function (that process their data)
    • unique key (that is a part of widget ID and will be used to tell the system if it should carry its state to next processing run)
    • boxed cloneable properties data
    • listed slots (simply: widget children)
    • named slots (similar to listed slots: widget children, but these ones have names assigned to them, so you can access them by name instead of by index)
  • WidgetUnit - an atomic element that renderers use to convert into target renderable data format for rendering engine of choice.
  widget! {{{
    TextBoxNode {
        text: "Hello World".to_owned(),

Component Function

Component functions are static functions that transforms input data (properties, state or neither of them) into output widget tree (usually used to simply wrap another components tree under one simple component, where at some point the simplest components returns final WidgetUnit's). They work together as a chain of transforms - root component applies some properties into children components using data from its own properties or state.

#[derive(PropsData, Debug, Default, Copy, Clone, Serialize, Deserialize)]
struct AppProps {
    pub index: usize,
fn app(context: WidgetContext) -> WidgetNode {
    let WidgetContext {
        props, named_slots, ..
    } = context;
    // easy way to get widgets from named slots.
    unpack_named_slots!(named_slots => { title, content });
    let index = props.read::<AppProps>().map(|p| p.index).unwrap_or(0);

    // we always return new widgets tree.
    widget! {
        // `#{key}` - provided value gives a unique name to node. keys allows widgets
        //      to save state between render calls. here we just pass key of this widget.
        // `vertical_box` - name of widget component to use, this one is built into RAUI.
        // `[...]` - listed widget slots. here we just put previously unpacked named slots.
        (#{index} vertical_box [


This may bring up a question: "If i use only functions and no objects to tell how to visualize UI, how do i keep some data between each render run?". For that you use states. State is a data that is stored between each processing calls as long as given widget is alive (that means: as long as widget id stays the same between two processing calls, to make sure your widget stays the same, you use keys - if no key is assigned, system will generate one for your widget but that will make it possible to die at any time if for example number of widget children changes in your common parent, your widget will change its id when key wasn't assigned). Some additional notes: While you use properties to send information down the tree and states to store widget data between processing cals, you can communicate with another widgets and host application using messages and signals! More than that, you can use hooks to listen for widget life cycle and perform actions there. It's worth noting that state uses properties to hold its data, so by that you can for example attach multiple hooks that each of them uses different data type as widget state, this opens the doors to be very creative when combining different hooks that operate on the same widget.

#[derive(PropsData, Debug, Default, Copy, Clone, Serialize, Deserialize)]
struct ButtonState {
    pub pressed: bool,


Hooks are used to put common widget logic into separate functions that can be chained in widgets and another hooks (you can build a reusable dependency chain of logic with that). Usually it is used to listen for life cycle events such as mount, change and unmount, additionally you can chain hooks to be processed sequentially in order they are chained in widgets and other hooks.

#[derive(MessageData, Debug, Copy, Clone, PartialEq, Eq)]
enum ButtonAction {

fn use_empty(context: &mut WidgetContext) {
    context.life_cycle.mount(|_| {
        println!("* EMPTY MOUNTED");

    context.life_cycle.change(|_| {
        println!("* EMPTY CHANGED");

    context.life_cycle.unmount(|_| {
        println!("* EMPTY UNMOUNTED");

// you use life cycle hooks for storing closures that will be called when widget will be
// mounted/changed/unmounted. they exists for you to be able to reuse some common logic across
// multiple components. each closure provides arguments such as:
// - widget id
// - widget state
// - message sender (this one is used to message other widgets you know about)
// - signal sender (this one is used to message application host)
// although this hook uses only life cycle, you can make different hooks that use many
// arguments, even use context you got from the component!
fn use_button(context: &mut WidgetContext) {
    context.life_cycle.mount(|context| {
        println!("* BUTTON MOUNTED: {}", context.id.key());
        let _ = context.state.write(ButtonState { pressed: false });

    context.life_cycle.change(|context| {
        println!("* BUTTON CHANGED: {}", context.id.key());
        for msg in context.messenger.messages {
            if let Some(msg) = msg.as_any().downcast_ref::<ButtonAction>() {
                let pressed = match msg {
                    ButtonAction::Pressed => true,
                    ButtonAction::Released => false,
                println!("* BUTTON ACTION: {:?}", msg);
                let _ = context.state.write(ButtonState { pressed });
                let _ = context.signals.write(*msg);

    context.life_cycle.unmount(|context| {
        println!("* BUTTON UNMOUNTED: {}", context.id.key());

fn button(mut context: WidgetContext) -> WidgetNode {
    let WidgetContext { key, props, .. } = context;
    println!("* PROCESS BUTTON: {}", key);

    widget! {
        (#{key} text_box: {props.clone()})

What happens under the hood:

  • Application calls button on a node
    • button calls use_button hook
      • use_button calls use_empty hook
    • use_button logic is executed
  • button logic is executed


RAUI exposes the Application::layout() API to allow use of virtual-to-real coords mapping and custom layout engines to perform widget tree positioning data, which is later used by custom UI renderers to specify boxes where given widgets should be placed. Every call to perform layouting will store a layout data inside Application, you can always access that data at any time. There is a DefaultLayoutEngine that does this in a generic way. If you find some part of its pipeline working different than what you've expected, feel free to create your custom layout engine!

let mut application = Application::default();
let mut layout_engine = DefaultLayoutEngine;
    "* TREE INSPECTION:\n{:#?}",
if application.layout(&mapping, &mut layout_engine).is_ok() {
    println!("* LAYOUT:\n{:#?}", application.layout_data());


RAUI allows you to ease and automate interactions with UI by use of Interactions Engine - this is just a struct that implements perform_interactions method with reference to Application, and all you should do there is to send user input related messages to widgets. There is DefaultInteractionsEngine that covers widget navigation, button and input field - actions sent from input devices such as mouse (or any single pointer), keyboard and gamepad. When it comes to UI navigation you can send raw NavSignal messages to the default interactions engine and despite being able to select/unselect widgets at will, you have typical navigation actions available: up, down, left, right, previous tab/screen, next tab/screen, also being able to focus text inputs and send text input changes to focused input widget. All interactive widget components that are provided by RAUI handle all NavSignal actions in their hooks, so all user has to do is to just activate navigation features for them (using NavItemActive unit props). RAUI integrations that want to just use use default interactions engine should make use of this struct composed in them and call its interact method with information about what input change was made. There is an example of that feature covered in Tetra integration crate (TetraInteractionsEngine struct).

NOTE: Interactions engines should use layout for pointer events so make sure that you rebuild layout before you perform interactions!

let mut application = Application::default();
// default interactions engine covers typical pointer + keyboard + gamepad navigation/interactions.
let mut interactions = DefaultInteractionsEngine::default();
// we interact with UI by sending interaction messages to the engine.
interactions.interact(Interaction::PointerMove(Vec2 { x: 200.0, y: 100.0 }));
    Vec2 { x: 200.0, y: 100.0 },
// navigation/interactions works only if we have navigable items (such as `button`) registered
// in some navigable container (usually containers with `nav_` prefix).
let tree = widget! {
    (#{"app"} nav_content_box [
        // by default navigable items are inactive which means we have to tell RAUI we activate
        // them to interact with them.
        (#{"button"} button: {NavItemActive} {
            content = (#{"icon"} image_box)
let mapping = CoordsMapping::new(Rect {
    left: 0.0,
    right: 1024.0,
    top: 0.0,
    bottom: 576.0,
    .layout(&mapping, &mut DefaultLayoutEngine)
// Since interactions engines require constructed layout to process interactions we have to
// process interactions after we layout the UI.
application.interact(&mut interactions).unwrap();


  • RAUI + Tetra In-Game An example of an In-Game integration of RAUI with custom Material theme, using Tetra as a renderer.

    RAUI + Tetra In-Game

  • RAUI + Tetra todo app An example of TODO app with Tetra renderer and dark theme Material component library.

    RAUI + Tetra todo app


Any contribution that improves quality of the RAUI toolset is highly appreciated.

  • If you have a feature request, create an Issue post and explain the goal of the feature along with the reason why it is needed and its pros and cons.
  • Whenever you would like to create na PR, please create your feature branch from next branch so when it gets approved it can be simply merged using GitHub merge button
  • All changes are staged into next branch and new versions are made out of its commits, master is considered stable/release branch.
  • Changes should pass tests, you run tests with: cargo test --all --features all.
  • This readme file is generated from the lib.rs documentation and can be re-generated by using cargo readme.


RAUI is still in early development phase, so prepare for these changes until v1.0:

  • Integrate RAUI into one public open source Rust game.
  • Write documentation.
  • Write MD book about how to use RAUI properly and make UI efficient.
  • Implement VDOM diffing algorithm for tree rebuilding optimizations.
  • Find a solution (or make it a feature) for moving from trait objects data into strongly typed data for properties and states.

Things that now are done:

  • Add suport for layouting.
  • Add suport for interactions (user input).
  • Create renderer for GGEZ game framework.
  • Create basic user components.
  • Create basic Hello World example application.
  • Decouple shared props from props (don't merge them, put shared props in context).
  • Create TODO app as an example.
  • Create In-Game app as an example.
  • Create renderer for Oxygengine game engine.
  • Add complex navigation system.
  • Create scroll box widget.
  • Add "immediate mode UI" builder to give alternative to macros-based declarative mode UI building (with zero overhead, it is an equivalent to declarative macros used by default, immediate mode and declarative mode widgets can talk to each other without a hassle).
  • Add data binding property type to easily mutate data from outside of the application.
  • Create tesselation renderer that produces Vertex + Index + Batch buffers ready for mesh renderers.
  • Create renderer for Tetra game framework.
  • Move from widget_component! and widget_hook! macro rules to pre_hooks and post_hooks function attributes.
  • Add derive PropsData and MessageData procedural macros to gradually replace the need to call implement_props_data! and implement_message_data! macros.
  • Add support for portals - an easy way to "teleport" sub-tree into another tree node (useful for modals and drag & drop).
  • Add support for View-Model for sharing data between host app and UI.


~59K SLoC