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.

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!

License: MIT OR Apache-2.0