# raui
RAUI is a renderer agnostic UI system that is heavily inspired by **React**'s declarative UI
composition and the **Unreal Engine Slate** widget components system.
> 🗣 **Pronunciation:** RAUI is pronounced like **"ra"** ( the Egyptian god ) + **"oui"**
> (french for "yes" ) — [Audio Example][pronounciation].
[pronounciation]: https://itinerarium.github.io/phoneme-synthesis/?w=/%27rawi/
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.
## Architecture
### [`Application`]
[`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.
### Widgets
Widgets are divided into three categories:
- **[`WidgetNode`]** - used as source UI trees (variant that can be either a component, unit or
none)
- **[`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.
### 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.
#### States
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.
### Hooks
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.
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
### Layouting
RAUI exposes the [`Application::layout()`][core::application::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!
### Interactivity
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 RAUI App crate
(`AppInteractionsEngine` struct).
**NOTE: Interactions engines should use layout for pointer events so make sure that you rebuild
layout before you perform interactions!**
[`Application`]: core::application::Application
[`WidgetNode`]: core::widget::node::WidgetNode
[`WidgetComponent`]: core::widget::component::WidgetComponent
[`WidgetUnit`]: core::widget::unit::WidgetUnit
[`DefaultLayoutEngine`]: core::layout::default_layout_engine::DefaultLayoutEngine
[`NavSignal`]: core::widget::component::interactive::navigation::NavSignal
[`NavItemActive`]: core::widget::component::interactive::navigation::NavItemActive
[`perform_interactions`]: core::interactive::InteractionsEngine::perform_interactions
[`interact`]:
core::interactive::default_interactions_engine::DefaultInteractionsEngine::interact
[`DefaultInteractionsEngine`]:
core::interactive::default_interactions_engine::DefaultInteractionsEngine
License: MIT OR Apache-2.0