FocusContainer Component

The FocusContainer component provides a flexible and primitive focus navigation system for CanvasEngine. It allows you to manage focus navigation between focusable child elements using keyboard, gamepad, or programmatic control.

This component is especially useful for creating menu systems, lists, and any interface that requires keyboard/gamepad navigation.

Basic Usage

html

<FocusContainer tabindex={0}>
  <Button tabindex={0} text="Button 1" />
  <Button tabindex={1} text="Button 2" />
  <Button tabindex={2} text="Button 3" />
</FocusContainer>

Properties

Property	Type	Description
`tabindex`	`number`	Focus index for the container (default: 0 if present)
`controls`	`Controls \| Signal<Controls>`	Controls configuration for automatic navigation
`onFocusChange`	`(index: number, element: Element \| null) => void`	Callback when focus changes
`autoScroll`	`boolean \| ScrollOptions`	Enable automatic scrolling to focused element (default: false)
`viewport`	`Viewport`	Viewport instance to use for scrolling (optional, uses context viewport by default)

You can also use all properties from DisplayObject.

Making Elements Focusable

To make an element focusable, add a tabindex attribute:

Canvas Components

For Canvas components (Button, Sprite, Rect, etc.), use the tabindex prop directly:

html

<FocusContainer tabindex={0}>
  <Button tabindex={0} text="Item 1" />
  <Button tabindex={1} text="Item 2" />
  <Button tabindex={2} text="Item 3" />
</FocusContainer>

DOM Elements

For DOM elements (inside DOMContainer), use attrs.tabindex:

html

<FocusContainer tabindex={0}>
  <DOMContainer>
    <button attrs={{ tabindex: 0 }}>Button 1</button>
    <button attrs={{ tabindex: 1 }}>Button 2</button>
    <button attrs={{ tabindex: 2 }}>Button 3</button>
  </DOMContainer>
</FocusContainer>

Here's a complete example demonstrating focus navigation within a DOMContainer with scoped CSS styling. This example shows how keyboard controls can be used to navigate through DOM buttons, with visual feedback through focus states.

Focus Navigation with DOM

Navigate through a scrollable list of DOM buttons using keyboard controls (arrow keys or gamepad)

Preview

Key Features

Keyboard Navigation: Use arrow keys (up/down) to navigate through the button list
Gamepad Support: Automatically works with gamepad directional buttons
Action Trigger: Press Space or Enter to trigger button action
Scoped Styles: CSS is scoped to the playground instance and properly injected
Smooth Transitions: Visual feedback with hover and focus states via CSS
Auto-Scroll: Container has overflow handling for scrollable content

The FocusContainer can automatically handle navigation when you provide a controls configuration:

html

<script>
import { signal } from 'canvasengine'

const controls = signal({
  up: {
    repeat: true,
    bind: 'up',
    keyDown() {
      console.log('Up pressed')
    }
  },
  down: {
    repeat: true,
    bind: 'down',
    keyDown() {
      console.log('Down pressed')
    }
  },
  action: {
    bind: ['space', 'enter'],
    keyDown() {
      console.log('Action pressed')
    }
  }
})
</script>

<FocusContainer tabindex={0} controls={controls}>
  <Button tabindex={0} text="Item 1" />
  <Button tabindex={1} text="Item 2" />
  <Button tabindex={2} text="Item 3" />
</FocusContainer>

The navigation controls automatically:

Up/Down arrows: Navigate to previous/next focusable element
Left/Right arrows: Navigate to previous/next (useful for horizontal lists)
Space/Enter: Trigger action on focused element (emits pointertap event)

Automatic Scrolling with Viewport

When using a Viewport with a long list, you can enable automatic scrolling to keep the focused element visible:

html

<Viewport worldWidth={2000} worldHeight={5000}>
  <FocusContainer tabindex={0} autoScroll={true}>
    <Button tabindex={0} y={0} text="Item 1" />
    <Button tabindex={1} y={100} text="Item 2" />
    <Button tabindex={2} y={200} text="Item 3" />
    <!-- ... many more items ... -->
    <Button tabindex={49} y={4900} text="Item 50" />
  </FocusContainer>
</Viewport>

Scroll Options

You can customize the scroll behavior:

html

<FocusContainer 
  tabindex={0} 
  autoScroll={{ 
    padding: 50,    // Padding around the element in pixels (default: 0)
    smooth: true,   // Enable smooth scrolling animation (default: false)
    center: true,   // Center the element in the viewport (default: true)
    duration: 300   // Animation duration in ms if smooth=true (default: 300)
  }}
>
  <!-- ... -->
</FocusContainer>

Reacting to Focus Changes

Using onFocusChange Callback

html

<script>
import { signal } from 'canvasengine'

const selectedIndex = signal(0)

const handleFocusChange = (index, element) => {
  if (index !== null) {
    selectedIndex.set(index)
    console.log('Focus changed to index:', index)
  }
}
</script>

<FocusContainer 
  tabindex={0} 
  onFocusChange={handleFocusChange}
>
  <Button tabindex={0} text="Item 1" />
  <Button tabindex={1} text="Item 2" />
  <Button tabindex={2} text="Item 3" />
</FocusContainer>

Two-way Synchronization with Signals

You can pass a signal directly to the tabindex property of the FocusContainer. This enables two-way synchronization:

When the focus changes (via keyboard, gamepad, or FocusManager), the signal is automatically updated.
When you update the signal manually, the focus automatically moves to the new index.

IMPORTANT

When using a signal for tabindex, you should not update the same signal inside onFocusChange or handleFocusChange, as this is handled automatically and could lead to unnecessary updates.

html

<script>
import { signal } from 'canvasengine'

const selectedIndex = signal(0)

// You can change the focus at any time by updating the signal
const goToSecondItem = () => {
  selectedIndex.set(1)
}
</script>

<!-- The signal is automatically synced with the focus state -->
<FocusContainer tabindex={selectedIndex}>
  <Button tabindex={0} text="Item 1" />
  <Button tabindex={1} text="Item 2" />
  <Button tabindex={2} text="Item 3" />
</FocusContainer>

<Button text="Go to Item 2" click={goToSecondItem} />

Using Hooks

You can use reactive hooks to track focus state:

html

<script>
import { useFocusIndex, useFocusedElement, useFocusChange } from 'canvasengine'
import { mount, effect } from 'canvasengine'

mount((element) => {
  // Find FocusContainer
  const findFocusContainer = (el) => {
    if (el.tag === 'FocusContainer') return el
    if (el.children) {
      for (const child of Array.isArray(el.children) ? el.children : [el.children]) {
        const found = findFocusContainer(child)
        if (found) return found
      }
    }
    return null
  }

  const focusContainer = findFocusContainer(element)
  if (focusContainer) {
    const containerId = focusContainer.componentInstance.getContainerId()
    
    // Get current index signal
    const focusIndex = useFocusIndex(containerId)
    effect(() => {
      console.log('Current focus index:', focusIndex?.())
    })
    
    // Get focused element signal
    const focusedElement = useFocusedElement(containerId)
    effect(() => {
      const element = focusedElement?.()
      if (element) {
        console.log('Focused element:', element)
      }
    })
    
    // Subscribe to focus changes
    useFocusChange(containerId, (index, element) => {
      console.log('Focus changed to index', index)
    })
  }
})
</script>

You can control focus programmatically using the FocusManager:

html

<script>
import { focusManager } from 'canvasengine'
import { mount } from 'canvasengine'

mount((element) => {
  const focusContainer = findFocusContainer(element)
  if (focusContainer) {
    const containerId = focusContainer.componentInstance.getContainerId()
    
    // Set focus to specific index
    focusManager.setIndex(containerId, 2)
    
    // Navigate to next/previous
    focusManager.navigate(containerId, 'next')
    focusManager.navigate(containerId, 'previous')
    
    // Get element at index
    const element = focusManager.getElement(containerId, 1)
  }
})
</script>

Complete Example

Here's a complete example showing a menu with visual feedback:

html

<script>
import { signal, computed } from 'canvasengine'

const selectedIndex = signal(0)
const items = signal([
  { id: 0, label: "Item 1", color: "#ff6b6b" },
  { id: 1, label: "Item 2", color: "#4ecdc4" },
  { id: 2, label: "Item 3", color: "#45b7d1" },
  { id: 3, label: "Item 4", color: "#f9ca24" },
  { id: 4, label: "Item 5", color: "#6c5ce7" },
])

const controls = signal({
  up: {
    repeat: true,
    bind: 'up',
    keyDown() {
      console.log('Up pressed')
    }
  },
  down: {
    repeat: true,
    bind: 'down',
    keyDown() {
      console.log('Down pressed')
    }
  },
  action: {
    bind: ['space', 'enter'],
    keyDown() {
      console.log('Action pressed on item', selectedIndex())
    }
  }
})

const handleFocusChange = (index, element) => {
  if (index !== null) {
    selectedIndex.set(index)
  }
}
</script>

<Canvas backgroundColor="#2c3e50">
  <Container x={400} y={300}>
    <Text 
      text="Focus Navigation Example" 
      x={0} 
      y={-250} 
      anchor={{ x: 0.5, y: 0.5 }}
      style={{ fontSize: 32, fill: "#ecf0f1" }}
    />
    
    <FocusContainer 
      tabindex={0} 
      controls={controls}
      onFocusChange={handleFocusChange}
    >
      <Container y={-100}>
        @for (item of items) {
          <Container y={@item.@id * 80}>
            <Rect
              tabindex={@item.@id}
              width={300}
              height={60}
              x={0}
              y={0}
              anchor={{ x: 0.5, y: 0.5 }}
              color={@item.@color}
              alpha={computed(() => selectedIndex() === @item.@id ? 1 : 0.5)}
            />
            <Text
              text={@item.@label}
              x={0}
              y={0}
              anchor={{ x: 0.5, y: 0.5 }}
              style={{ fontSize: 24, fill: "#ffffff" }}
            />
            @if (selectedIndex() === @item.@id) {
              <Rect
                width={320}
                height={80}
                x={0}
                y={0}
                anchor={{ x: 0.5, y: 0.5 }}
                color="#ffffff"
                alpha={0.2}
              />
            }
          </Container>
        }
      </Container>
    </FocusContainer>
  </Container>
</Canvas>

Long List with Viewport

For long lists that require scrolling:

html

<script>
import { signal } from 'canvasengine'

const items = signal(
  Array.from({ length: 50 }, (_, i) => ({
    id: i,
    label: `Item ${i + 1}`,
    y: i * 100
  }))
)

const controls = signal({
  up: { repeat: true, bind: 'up' },
  down: { repeat: true, bind: 'down' },
  action: { bind: ['space', 'enter'] }
})
</script>

<Viewport worldWidth={2000} worldHeight={5000}>
  <FocusContainer 
    tabindex={0} 
    controls={controls}
    autoScroll={{ smooth: true, center: true }}
  >
    @for (item of items) {
      <Button 
        tabindex={@item.@id} 
        y={@item.@y} 
        text={@item.@label}
      />
    }
  </FocusContainer>
</Viewport>

API Reference

FocusManager

The FocusManager is a singleton that manages all focus containers. You can access it directly:

typescript

import { focusManager } from 'canvasengine'

// Register a container (done automatically by FocusContainer)
focusManager.registerContainer(id, data)

// Navigate
focusManager.navigate(containerId, 'next' | 'previous')

// Set focus index
focusManager.setIndex(containerId, index)

// Get element at index
const element = focusManager.getElement(containerId, index)

// Get signals
const indexSignal = focusManager.getCurrentIndexSignal(containerId)
const elementSignal = focusManager.getFocusedElementSignal(containerId)

Hooks

`useFocusIndex(containerId: string)`

Returns the current focus index signal for a container.

typescript

const focusIndex = useFocusIndex('my-container')
effect(() => {
  console.log('Current index:', focusIndex?.())
})

`useFocusedElement(containerId: string)`

Returns the current focused element signal for a container.

typescript

const focusedElement = useFocusedElement('my-container')
effect(() => {
  const element = focusedElement?.()
  if (element) {
    console.log('Focused element:', element)
  }
})

`useFocusChange(containerId: string, callback: (index: number | null, element: Element | null) => void)`

Subscribes to focus changes and calls the callback whenever focus changes.

typescript

useFocusChange('my-container', (index, element) => {
  console.log('Focus changed to index', index)
})

Best Practices

Use sequential tabindex values: Start from 0 and increment by 1 for each focusable element
Handle focus changes reactively: Use onFocusChange or hooks to update UI state
Enable auto-scroll for long lists: Use autoScroll={true} when elements might be outside the viewport
Combine with Controls: Provide a controls prop for automatic keyboard/gamepad navigation
Visual feedback: Always provide visual indication of which element is focused

Limitations

Focusable elements must be direct or nested children of the FocusContainer
Tabindex values should be unique within a container
Elements with tabindex < 0 are not registered as focusable

Common Properties

Property	Type	Description
x	number	X-coordinate position of the display object.
y	number	Y-coordinate position of the display object.
width	number	Width of the display object.
height	number	Height of the display object.
scale	object	Scale of the display object.
anchor	object	Anchor point of the display object.
skew	object	Skew of the display object.
tint	number	Tint color of the display object.
rotation	number	Rotation of the display object in radians.
angle	number	Rotation of the display object in degrees.
zIndex	number	Z-index of the display object.
roundPixels	boolean	Whether to round pixel values.
cursor	string	Cursor style when hovering over the display object.
visible	boolean	Visibility of the display object.
alpha	number	Alpha transparency of the display object.
pivot	object	Pivot point of the display object.
filters	array	Filters applied to the display object.
maskOf	Element	Element that this display object masks.
blendMode	string	Blend mode for rendering.
filterArea	object	Filter area for rendering.

Layout Properties

Pour obtenir la documentation complète et détaillée sur toutes les propriétés de mise en page, consultez la documentation officielle de PixiJS Layout.

Sizing and Dimensions

Property	Type	Description
width	number/string	Width of the display object. Accepts pixels or percentage (e.g. '50%').
height	number/string	Height of the display object. Accepts pixels or percentage (e.g. '50%').
minWidth	number/string	Minimum width the object can shrink to.
minHeight	number/string	Minimum height the object can shrink to.
maxWidth	number/string	Maximum width the object can expand to.
maxHeight	number/string	Maximum height the object can expand to.
aspectRatio	number	Ratio between width and height (e.g. 1.5 for 3:2 ratio).

Flex Layout

Property	Type	Description
flexDirection	string	Direction of flex items. Values: 'row', 'column', 'row-reverse', 'column-reverse'.
flexWrap	string	Whether items wrap. Values: 'wrap', 'nowrap', 'wrap-reverse'.
justifyContent	string	Alignment along main axis. Values: 'flex-start', 'flex-end', 'center', 'space-between', 'space-around'.
alignItems	string	Alignment along cross axis. Values: 'flex-start', 'flex-end', 'center', 'stretch', 'baseline'.
alignContent	string	Alignment of lines with multiple items. Values: 'flex-start', 'flex-end', 'center', 'stretch', 'space-between', 'space-around'.
alignSelf	string	Override of parent's alignItems for specific item.
flexGrow	number	Grow factor of item relative to other items.
flexShrink	number	Shrink factor of item relative to other items.
flexBasis	number/string	Initial size of item before flex growing/shrinking.
gap	number/object	Gap between items.
rowGap	number	Gap between rows.
columnGap	number	Gap between columns.

Positioning

Property	Type	Description
positionType	string	Type of positioning. Values: 'relative', 'absolute', 'static'.
top	number/string	Distance from the top edge.
right	number/string	Distance from the right edge.
bottom	number/string	Distance from the bottom edge.
left	number/string	Distance from the left edge.

Spacing, Margins and Borders

Property	Type	Description
margin	number/array	Space outside border box. Can be single value or array for different sides.
padding	number/array	Space inside border box. Can be single value or array for different sides.
border	number/array	Border width. Can be single value or array for different sides.

Object Fitting and Alignment

Property	Type	Description
objectFit	string	How object is resized to fit layout box. Values: 'contain', 'cover', 'fill', 'none', 'scale-down'.
objectPosition	string	Anchor point of object inside layout box. E.g. 'center', 'top left'.
transformOrigin	string	Pivot point for rotation and scaling of layout box.

Shadow

Property	Type	Description
blur	number	Blur strength.
color	number	Color of the shadow.
offset	object	Offset of the shadow.
quality	number	Quality of the shadow.

Hook before destroy

html

<script>
  import {
    signal,
    animatedSignal,
    effect,
    animatedSequence,
  } from "canvasengine";
  import MyViewport from "./viewport.ce";
  
  let bool = signal(true)
  const opacity = animatedSignal(1, { duration: 500 });

  const click = async () => {
    bool.set(!bool())
  }

  const beforeDestroy = async () => {
    await animatedSequence([
      () => opacity.set(0),
    ])
    console.log("before destroy")
  }
</script>


<Canvas antialias={true}>
     <Container onBeforeDestroy={beforeDestroy}>
        @if (bool) {
            <Rect width={300} height={300} color="red" alpha={opacity} click />
        }
    </Container>
</Canvas>

FocusContainer Component

Basic Usage

Properties

Making Elements Focusable

Canvas Components

DOM Elements

DOM Navigation with Scoped Styles

Focus Navigation with DOM

Key Features

Navigation with Controls

Automatic Scrolling with Viewport

Scroll Options

Reacting to Focus Changes

Using onFocusChange Callback

Two-way Synchronization with Signals

Using Hooks

Programmatic Navigation

Complete Example

Long List with Viewport

API Reference

FocusManager

Hooks

`useFocusIndex(containerId: string)`

`useFocusedElement(containerId: string)`

`useFocusChange(containerId: string, callback: (index: number | null, element: Element | null) => void)`

Best Practices

Limitations

Common Properties

Layout Properties

Sizing and Dimensions

Flex Layout

Positioning

Spacing, Margins and Borders

Object Fitting and Alignment

Shadow

Hook before destroy

FocusContainer Component ​

Basic Usage ​

Properties ​

Making Elements Focusable ​

Canvas Components ​

DOM Elements ​

DOM Navigation with Scoped Styles ​

Focus Navigation with DOM

Key Features ​

Navigation with Controls ​

Automatic Scrolling with Viewport ​

Scroll Options ​

Reacting to Focus Changes ​

Using onFocusChange Callback ​

Two-way Synchronization with Signals ​

Using Hooks ​

Programmatic Navigation ​

Complete Example ​

Long List with Viewport ​

API Reference ​

FocusManager ​

Hooks ​

useFocusIndex(containerId: string) ​

useFocusedElement(containerId: string) ​

useFocusChange(containerId: string, callback: (index: number | null, element: Element | null) => void) ​

Best Practices ​

Limitations ​

Common Properties ​

Layout Properties ​

Sizing and Dimensions ​

Flex Layout ​

Positioning ​

Spacing, Margins and Borders ​

Object Fitting and Alignment ​

Shadow ​

Hook before destroy ​

FocusContainer Component

Basic Usage

Properties

Making Elements Focusable

Canvas Components

DOM Elements

DOM Navigation with Scoped Styles

Key Features

Navigation with Controls

Automatic Scrolling with Viewport

Scroll Options

Reacting to Focus Changes

Using onFocusChange Callback

Two-way Synchronization with Signals

Using Hooks

Programmatic Navigation

Complete Example

Long List with Viewport

API Reference

FocusManager

Hooks

`useFocusIndex(containerId: string)`

`useFocusedElement(containerId: string)`

`useFocusChange(containerId: string, callback: (index: number | null, element: Element | null) => void)`

Best Practices

Limitations

Common Properties

Layout Properties

Sizing and Dimensions

Flex Layout

Positioning

Spacing, Margins and Borders

Object Fitting and Alignment

Shadow

Hook before destroy