dawarich/app/javascript/maps_maplibre/layers/fog_layer.js

/**
 * Fog of war layer
 * Shows explored vs unexplored areas using canvas overlay
 * Does not extend BaseLayer as it uses canvas instead of MapLibre layers
 */
export class FogLayer {
  constructor(map, options = {}) {
    this.map = map
    this.id = 'fog'
    this.visible = options.visible !== undefined ? options.visible : false
    this.canvas = null
    this.ctx = null
    this.clearRadius = options.clearRadius || 1000 // meters
    this.points = []
  }

  add(data) {
    this.points = data.features || []
    this.createCanvas()
    if (this.visible) {
      this.show()
    }
    this.render()
  }

  update(data) {
    this.points = data.features || []
    this.render()
  }

  createCanvas() {
    if (this.canvas) return

    // Create canvas overlay
    this.canvas = document.createElement('canvas')
    this.canvas.className = 'fog-canvas'
    this.canvas.style.position = 'absolute'
    this.canvas.style.top = '0'
    this.canvas.style.left = '0'
    this.canvas.style.pointerEvents = 'none'
    this.canvas.style.zIndex = '10'
    this.canvas.style.display = this.visible ? 'block' : 'none'

    this.ctx = this.canvas.getContext('2d')

    // Add to map container
    const mapContainer = this.map.getContainer()
    mapContainer.appendChild(this.canvas)

    // Update on map move/zoom/resize
    this.map.on('move', () => this.render())
    this.map.on('zoom', () => this.render())
    this.map.on('resize', () => this.resizeCanvas())

    this.resizeCanvas()
  }

  resizeCanvas() {
    if (!this.canvas) return

    const container = this.map.getContainer()
    this.canvas.width = container.offsetWidth
    this.canvas.height = container.offsetHeight
    this.render()
  }

  render() {
    if (!this.canvas || !this.ctx || !this.visible) return

    const { width, height } = this.canvas

    // Clear canvas
    this.ctx.clearRect(0, 0, width, height)

    // Draw fog overlay
    this.ctx.fillStyle = 'rgba(0, 0, 0, 0.6)'
    this.ctx.fillRect(0, 0, width, height)

    // Clear circles around visited points
    this.ctx.globalCompositeOperation = 'destination-out'

    this.points.forEach(feature => {
      const coords = feature.geometry.coordinates
      const point = this.map.project(coords)

      // Calculate pixel radius based on zoom level
      const metersPerPixel = this.getMetersPerPixel(coords[1])
      const radiusPixels = this.clearRadius / metersPerPixel

      this.ctx.beginPath()
      this.ctx.arc(point.x, point.y, radiusPixels, 0, Math.PI * 2)
      this.ctx.fill()
    })

    this.ctx.globalCompositeOperation = 'source-over'
  }

  getMetersPerPixel(latitude) {
    const earthCircumference = 40075017 // meters at equator
    const latitudeRadians = latitude * Math.PI / 180
    const zoom = this.map.getZoom()
    return earthCircumference * Math.cos(latitudeRadians) / (256 * Math.pow(2, zoom))
  }

  show() {
    this.visible = true
    if (this.canvas) {
      this.canvas.style.display = 'block'
      this.render()
    }
  }

  hide() {
    this.visible = false
    if (this.canvas) {
      this.canvas.style.display = 'none'
    }
  }

  toggle(visible = !this.visible) {
    if (visible) {
      this.show()
    } else {
      this.hide()
    }
  }

  remove() {
    if (this.canvas) {
      this.canvas.remove()
      this.canvas = null
      this.ctx = null
    }

    // Remove event listeners
    this.map.off('move', this.render)
    this.map.off('zoom', this.render)
    this.map.off('resize', this.resizeCanvas)
  }
}