Interactivity

Interactivity is done through observers. Let’s recap on what observers are:

Observers are a type of a one-shot system, that is run when specific event is triggered on specific entity.

We define these observers, which take On<E: Event> that specify for which event it listens. Then we attach it to a spawned entity (local observer).

We can listen to ANY event we want, even our own custom events. But in practise, the Pointer<T> events are the most common. These events are related to bevy_picking, which are fired when for example a mouse cursor clicks when pointing at the entity.

• Pointer<Click>
• Pointer<Over>
• Pointer<Out>
• Pointer<Down>
• Pointer<Up>
• Pointer<Drag>

These events also have metadata that you can access through the On event, like for example which mouse button was pressed.

Example

ui.spawn((
    Name::new("Exit Button"),
    UiLayout::window()
        .anchor(Anchor::Center)
        .pos(Rl((50.0, 50.0)))
        .size((200.0, 50.0))
        .pack(),
    Sprite::from_image(asset_server.load("images/button.png")),

// Interactivity is done through observers, you can query anything here
)).observe(|_: On<Pointer<Click>>, mut exit: MessageWriter<AppExit>| {
    
    // Close the app on click
    exit.write(AppExit::Success);
});