Circle

Circles are circular overlays that can be drawn on the map with customizable radius, stroke, and fill properties. They are useful for representing areas, ranges, or zones.

Composable Functions

Basic Circle

For a small number of circles, you can specify options directly. Specifying an id helps prevent unnecessary recomposition.

@Composable
fun MapViewScope.Circle(
    center: GeoPointInterface,
    radiusMeters: Double,
    geodesic: Boolean = false,
    strokeColor: Color = Color.Red,
    strokeWidth: Dp = 2.dp,
    fillColor: Color = Color.White.copy(alpha = 0.5f),
    extra: Serializable? = null,
    id: String? = null
)

Circle with State

For a large number of circles or when moving circles, using state is recommended. Specifying an id helps prevent unnecessary recomposition.

CircleState(
    center: GeoPointInterface,
    radiusMeters: Double,
    geodesic: Boolean = false,
    strokeColor: Color = Color.Red,
    strokeWidth: Dp = 2.dp,
    fillColor: Color = Color.White.copy(alpha = 0.5f),
    extra: Serializable? = null,
    id: String? = null
)

@Composable
fun MapViewScope.Circle(state: CircleState)

Parameters

• center: Geographic center point of the circle (GeoPointInterface)
• radiusMeters: Radius in meters (Double)
• geodesic: Whether to draw the circle using geodesic edges that follow the Earth’s curvature (default: false)
• strokeColor: Color of the circle’s border (default: Color.Red)
• strokeWidth: Width of the border line (default: 2.dp)
• fillColor: Fill color of the circle interior (default: semi-transparent white)
• extra: Additional data attached to the circle (Serializable?)
• id: Unique identifier for the circle (String?)

Usage Examples

Basic Circle

// Replace MapView with your chosen map provider, such as GoogleMapView, MapboxMapView
MapView(state = mapViewState) {
    Circle(
        center = GeoPoint.fromLatLong(37.7749, -122.4194),
        radiusMeters = 1000.0, // 1km radius
        strokeColor = Color.Blue,
        fillColor = Color.Blue.copy(alpha = 0.3f),
        id = "downtown-area"
    )
}

Interactive Circle with Markers

Based on the example app, here’s how to create an interactive circle with draggable markers:

@Composable
fun InteractiveCircleExample() {
    var centerPosition by remember {
        mutableStateOf(GeoPoint.fromLatLong(37.7749, -122.4194))
    }
    var radiusMeters by remember { mutableStateOf(1000.0) }

    // Calculate edge marker position
    val edgePosition = remember(centerPosition, radiusMeters) {
        // Calculate a point that's 'radiusMeters' meters away from center
        // This is simplified - actual calculation would consider Earth's curvature
        val latOffset = radiusMeters / 111000.0 // Rough meters per degree latitude
        GeoPoint.fromLatLong(
            centerPosition.latitude + latOffset,
            centerPosition.longitude
        )
    }

    val circleState = CircleState(
        center = centerPosition,
        radiusMeters = radiusMeters,
        strokeColor = Color.Blue,
        fillColor = Color.Blue.copy(alpha = 0.3f),
        clickable = true,
        onClick = { circleEvent ->
            println("Circle clicked at: ${circleEvent.clicked}")
        }
    )

    val centerMarker = MarkerState(
        position = centerPosition,
        icon = DefaultIcon(
            fillColor = Color.Blue,
            label = "C"
        ),
        draggable = false
    )

    val edgeMarker = MarkerState(
        position = edgePosition,
        icon = DefaultIcon(
            fillColor = Color.Green,
            label = "E"
        ),
        draggable = true,
        onDrag = { markerState ->
            // Calculate new radius based on edge marker position
            val distance = calculateDistance(centerPosition, markerState.position)
            radiusMeters = distance
        }
    )

    // Replace MapView with your chosen map provider, such as GoogleMapView, MapboxMapView
    MapView(
        state = mapViewState
    ) {
        Circle(circleState)
        Marker(centerMarker)
        Marker(edgeMarker)
    }
}

Dynamic Circle Updates

@Composable
fun DynamicCircleExample() {
    var circleRadius by remember { mutableStateOf(500.0) }
    var circleColor by remember { mutableStateOf(Color.Blue) }

    Column {
        // Controls
        Slider(
            value = circleRadius.toFloat(),
            onValueChange = { circleRadius = it.toDouble() },
            valueRange = 100f..2000f,
            modifier = Modifier.padding(16.dp)
        )

        Row {
            Button(onClick = { circleColor = Color.Red }) {
                Text("Red")
            }
            Button(onClick = { circleColor = Color.Blue }) {
                Text("Blue")
            }
            Button(onClick = { circleColor = Color.Green }) {
                Text("Green")
            }
        }

        // Map with dynamic circle
        // Replace MapView with your chosen map provider, such as GoogleMapView, MapboxMapView
        MapView(state = mapViewState) {
            Circle(
                center = GeoPoint.fromLatLong(37.7749, -122.4194),
                radiusMeters = circleRadius,
                strokeColor = circleColor,
                fillColor = circleColor.copy(alpha = 0.3f)
            )

            // Center marker
            Marker(
                position = GeoPoint.fromLatLong(37.7749, -122.4194),
                icon = DefaultIcon(
                    fillColor = circleColor,
                    label = "${circleRadius.toInt()}m"
                )
            )
        }
    }
}

Event Handling

Circle interactions are handled with your map provider component:

// Replace MapView with your chosen map provider, such as GoogleMapView, MapboxMapView
MapView(
    state = mapViewState
) {
    Circle(
        center = GeoPoint.fromLatLong(37.7749, -122.4194),
        radiusMeters = 1000.0,
        clickable = true,
        extra = "Clickable circle",
        onClick = { circleEvent ->
            val circle = circleEvent.state
            val clickPoint = circleEvent.clicked

            println("Circle clicked:")
            println("  Center: ${circle.center}")
            println("  Radius: ${circle.radiusMeters}m")
            println("  Click point: ${clickPoint}")
            println("  Extra data: ${circle.extra}")
        }
    )
}

Styling Options

Stroke Styles

// Thin border
Circle(
    center = center,
    radiusMeters = 500.0,
    strokeColor = Color.Black,
    strokeWidth = 1.dp
)

// Thick border
Circle(
    center = center,
    radiusMeters = 500.0,
    strokeColor = Color.Black,
    strokeWidth = 5.dp
)

// No border
Circle(
    center = center,
    radiusMeters = 500.0,
    strokeColor = Color.Transparent,
    strokeWidth = 0.dp
)

Fill Styles

// Solid fill
Circle(
    center = center,
    radiusMeters = 500.0,
    fillColor = Color.Red
)

// Semi-transparent fill
Circle(
    center = center,
    radiusMeters = 500.0,
    fillColor = Color.Red.copy(alpha = 0.5f)
)

// No fill
Circle(
    center = center,
    radiusMeters = 500.0,
    fillColor = Color.Transparent
)

Circle Identification

Using the ID Property

The id property provides a unique identifier for circles, enabling efficient tracking and management:

@Composable
fun CircleIdentificationExample() {
    val mapViewState = rememberGoogleMapViewState()

    // Use ID in event handling
    val onCircleClick: OnCircleEventHandler = { circleEvent ->
        when (circleEvent.state.id) {
            "zone-a" -> handleZoneA()
            "zone-b" -> handleZoneB()
            else -> handleUnknownZone()
        }
    }

    // Create circles with unique IDs
    val circles = listOf(
        CircleState(
            center = GeoPoint.fromLatLong(37.7749, -122.4194),
            radiusMeters = 1000.0,
            strokeColor = Color.Red,
            fillColor = Color.Red.copy(alpha = 0.3f),
            id = "zone-a",
            onClick = onCircleClick
        ),
        CircleState(
            center = GeoPoint.fromLatLong(37.7849, -122.4094),
            radiusMeters = 1500.0,
            strokeColor = Color.Blue,
            fillColor = Color.Blue.copy(alpha = 0.3f),
            id = "zone-b",
            onClick = onCircleClick
        )
    )

    MapView(
        state = mapViewState
    ) {
        circles.forEach { circle -> Circle(circle) }
    }
}

private fun handleZoneA() {
    println("Zone A clicked")
}

private fun handleZoneB() {
    println("Zone B clicked")
}

private fun handleUnknownZone() {
    println("Unknown zone clicked")
}

Benefits of Using IDs

• Unique Identification: Distinguish between circles even when they have similar properties
• Event Handling: Simplifies click event handling and area-specific logic
• State Management: Enables efficient updates and selection management
• Performance: Facilitates optimized rendering and updates

Best Practices

1. Use Appropriate Radius: Consider the map zoom level when setting circle radius
2. Provide Unique IDs: Always set unique id values when working with multiple circles
3. Color Contrast: Ensure stroke and fill colors provide good visibility on the map
4. Performance: Avoid creating too many large circles as they may impact rendering performance
5. Interactive Feedback: Provide visual feedback when circles are clickable
6. Consistent Styling: Maintain consistent circle styling across your application
7. Extra Data: Use the extra parameter to store metadata for event handling
8. Z-Index Management: Consider drawing order when circles overlap