MapLibre Camera

Camera control patterns using the useMapCamera composable.

Announce: "I'm using maplibre-camera to implement camera control correctly."

The Iron Rule

NEVER access

map.flyTo()

useMapCamera

// WRONG: Direct map access
const map = inject(MAP_KEY)
map.flyTo({ center: [lng, lat], zoom: 10 })

// CORRECT: Use the composable
const { flyTo } = useMapCamera()
await flyTo({ center: [lng, lat], zoom: 10 })

useMapCamera Composable

Location:

src/composables/map/useMapCamera.ts

What It Provides

const {
  // State
  center,        // Ref<{lng, lat}> - current center
  zoom,          // Ref<number> - current zoom
  pitch,         // Ref<number> - current pitch (0-85)
  bearing,       // Ref<number> - current bearing (0-360)
  isAnimating,   // Ref<boolean> - animation in progress
  isLoaded,      // Computed<boolean> - map ready
  
  // Methods (all return Promise<void>)
  flyTo,         // Smooth arc animation
  easeTo,        // Linear interpolation
  jumpTo,        // Instant move
  fitBounds,     // Fit to bounding box
  
  // Lifecycle
  cleanup        // Remove event listeners
} = useMapCamera(options)

Options

interface UseMapCameraOptions {
  initialCenter?: [number, number]  // Default: [0, 20]
  initialZoom?: number              // Default: 2
  initialPitch?: number             // Default: 0
  initialBearing?: number           // Default: 0
  syncFromMap?: boolean             // Default: true - sync state from map events
}

Animation Methods

flyTo - Dramatic Arc Animation

await flyTo({
  center: [2.3522, 48.8566],  // Paris
  zoom: 12,
  pitch: 45,
  bearing: 30,
  duration: 3000  // 3 seconds
})
// Promise resolves when animation completes

Use for: Dramatic camera moves, showing user a new location

easeTo - Linear Interpolation

await easeTo({
  center: [2.3522, 48.8566],
  zoom: 12,
  duration: 1000
})

Use for: Quick, responsive moves (faster than flyTo)

jumpTo - Instant Move

jumpTo({
  center: [2.3522, 48.8566],
  zoom: 12
})
// No promise - instant

Use for: Initial positioning, resetting view

fitBounds - Fit to Bounding Box

await fitBounds(
  [[minLng, minLat], [maxLng, maxLat]],
  { padding: 50, maxZoom: 15 }
)

Use for: Showing all candidates, fitting to region

Feedback Loop Prevention

The composable prevents infinite loops between state and map:

// Inside useMapCamera
let isProgrammaticMove = false

function flyTo(options) {
  isProgrammaticMove = true  // Flag: we initiated this
  map.flyTo(options)
  map.once('moveend', () => {
    isProgrammaticMove = false
  })
}

// Map event listener
map.on('move', () => {
  if (!isProgrammaticMove) {
    // Only sync state if user moved the map
    center.value = map.getCenter()
  }
})

This prevents: Component → updates state → triggers watcher → calls map method → triggers event → updates state → ...

Globe Visibility Filtering

For globe projection, filter markers to visible hemisphere:

// src/composables/map/useGlobeVisibility.ts
export function isVisibleOnGlobe(
  pointLng: number,
  pointLat: number,
  centerLng: number,
  centerLat: number
): boolean {
  const toRad = (d: number) => d * Math.PI / 180
  const lat1 = toRad(pointLat)
  const lat2 = toRad(centerLat)
  const dLng = toRad(pointLng - centerLng)
  
  // Cosine of angle between points on sphere
  const cosAngle = 
    Math.sin(lat1) * Math.sin(lat2) + 
    Math.cos(lat1) * Math.cos(lat2) * Math.cos(dLng)
  
  // Visible if on front hemisphere (with small buffer)
  return cosAngle > -0.1
}

Use with computed to filter candidates:

const visibleCandidates = computed(() => 
  candidates.value.filter(c => 
    isVisibleOnGlobe(c.lng, c.lat, center.value.lng, center.value.lat)
  )
)

Cinematic Intro Animation

For custom animations beyond built-in methods:

// src/composables/map/useCinematicIntro.ts
export function useCinematicIntro() {
  async function animate(
    map: MapLibreMap,
    target: { lng: number, lat: number },
    options: { duration?: number, signal?: AbortSignal }
  ): Promise<void> {
    return new Promise((resolve) => {
      const startTime = performance.now()
      let rafId: number
      
      function frame(currentTime: number) {
        if (options.signal?.aborted) {
          cancelAnimationFrame(rafId)
          resolve()
          return
        }
        
        const progress = (currentTime - startTime) / (options.duration || 3000)
        const eased = easeOutCubic(Math.min(progress, 1))
        
        // Interpolate camera
        map.jumpTo({
          center: lerp(startCenter, target, eased),
          zoom: lerp(startZoom, targetZoom, eased)
        })
        
        if (progress < 1) {
          rafId = requestAnimationFrame(frame)
        } else {
          resolve()
        }
      }
      
      rafId = requestAnimationFrame(frame)
    })
  }
  
  return { animate }
}

Anti-Patterns

DON'T: Access Map Directly

// WRONG
const map = inject(MAP_KEY)
map.flyTo({ center })

// CORRECT
const { flyTo } = useMapCamera()
await flyTo({ center })

DON'T: Forget to Await Animations

// WRONG: May cause race conditions
flyTo({ center: a })
flyTo({ center: b })  // Interrupts first animation!

// CORRECT: Await each animation
await flyTo({ center: a })
await flyTo({ center: b })

DON'T: Check Map Before isLoaded

// WRONG: Map may not be ready
onMounted(() => {
  flyTo({ center })  // May fail!
})

// CORRECT: Wait for map
watch(isLoaded, (loaded) => {
  if (loaded) flyTo({ center })
})

References

See

references/camera-examples.md