perf(map): viewport culling, label limit, scroll refresh, SetVisible gating

feature/map/src/main/java/com/rtbishop/look4sat/feature/map/MapScreen.kt

@@ -90,6 +90,10 @@ import com.rtbishop.look4sat.core.presentation.TopBar
 import com.rtbishop.look4sat.core.presentation.isVerticalLayout
 import com.rtbishop.look4sat.core.presentation.layoutPadding
 import org.osmdroid.tileprovider.tilesource.XYTileSource
+import org.osmdroid.events.DelayedMapListener
+import org.osmdroid.events.MapListener
+import org.osmdroid.events.ScrollEvent
+import org.osmdroid.events.ZoomEvent
 import org.osmdroid.util.GeoPoint
 import org.osmdroid.views.CustomZoomButtonsController
 import org.osmdroid.views.MapView
@@ -145,6 +149,21 @@ fun MapDestination() {
     val viewModel: MapViewModel = viewModel(factory = MapViewModel.factory(container))
     val uiState by viewModel.uiState.collectAsStateWithLifecycle()
     val mapView = rememberMapViewWithLifecycle()
+    val lifecycle = LocalLifecycleOwner.current.lifecycle
+    DisposableEffect(lifecycle) {
+        val observer = LifecycleEventObserver { _, event ->
+            when (event) {
+                Lifecycle.Event.ON_START -> viewModel.onAction(MapAction.SetVisible(true))
+                Lifecycle.Event.ON_STOP -> viewModel.onAction(MapAction.SetVisible(false))
+                else -> {}
+            }
+        }
+        lifecycle.addObserver(observer)
+        onDispose {
+            lifecycle.removeObserver(observer)
+            viewModel.onAction(MapAction.SetVisible(false))
+        }
+    }
     MapScreen(uiState, viewModel::onAction, mapView)
 }
 
@@ -731,6 +750,27 @@ private fun setStationPosition(stationPos: GeoPos, mapView: MapView) {
     }
 }
 
+/** Above this many satellites inside the viewport labels are dropped in favor of a single
+ * shared dot icon. Per-satellite label bitmaps cost ~90KB each, so drawing thousands of them
+ * exhausts memory and stalls the UI thread — and overlapping labels are unreadable anyway. */
+private const val LABEL_LIMIT = 128
+
+/** Degrees of space around the viewport so markers don't pop in at the edges */
+private const val VIEWPORT_MARGIN = 8.0
+
+/** Debounce for viewport-driven marker refreshes, in milliseconds */
+private const val MAP_LISTENER_DELAY = 128L
+
+/** Shared dot icon used when too many satellites are visible to label them */
+private var dotIcon: Drawable? = null
+
+/** Scratch list reused every frame to avoid per-tick allocation */
+private val visibleSats = ArrayList<Pair<OrbitalObject, GeoPos>>()
+
+/** Last emitted positions, replayed on scroll/zoom so culled markers appear without waiting for a tick */
+private var lastPositions: Map<OrbitalObject, GeoPos>? = null
+private var lastAction: ((OrbitalObject) -> Unit)? = null
+
 /** Pool of reusable Marker objects keyed by satellite name, to avoid re-creation every frame */
 private val markerPool = HashMap<String, Marker>()
 private var lastMapView: MapView? = null
@@ -741,13 +781,20 @@ private fun setPositions(
     action: (OrbitalObject) -> Unit
 ) {
     try {
+        lastPositions = posMap
+        lastAction = action
         // Clear caches when the MapView instance changes (e.g. config change)
         if (lastMapView !== mapView) {
             lastMapView = mapView
             markerPool.clear()
             iconCache.evictAll()
+            dotIcon = null
             footprintPolyline = null
             footprintPoints = null
+            mapView.addMapListener(DelayedMapListener(object : MapListener {
+                override fun onScroll(event: ScrollEvent?) = refreshPositions(mapView)
+                override fun onZoom(event: ZoomEvent?) = refreshPositions(mapView)
+            }, MAP_LISTENER_DELAY))
         }
         // Reuse the existing FolderOverlay — creating a new one and replacing it
         // causes osmdroid to detach shared Marker objects, making them invisible.
@@ -756,17 +803,48 @@ private fun setPositions(
         }
         folder.items.clear()
 
-        val activeNames = HashSet<String>(posMap.size)
-        posMap.forEach { (satellite, geoPos) ->
+        // Cull satellites outside the viewport: only meaningful once zoomed in, but that is
+        // exactly when marker labels are shown and drawing is most expensive.
+        visibleSats.clear()
+        if (mapView.width > 0 && mapView.height > 0) {
+            val box = mapView.boundingBox
+            val latNorth = box.latNorth + VIEWPORT_MARGIN
+            val latSouth = box.latSouth - VIEWPORT_MARGIN
+            val lonWest = box.lonWest - VIEWPORT_MARGIN
+            val lonEast = box.lonEast + VIEWPORT_MARGIN
+            val wrapsDateLine = box.lonWest > box.lonEast
+            for ((satellite, geoPos) in posMap) {
+                val lat = geoPos.latitude
+                if (lat !in latSouth..latNorth) continue
+                val lon = geoPos.longitude
+                val isLonVisible = if (wrapsDateLine) lon >= lonWest || lon <= lonEast
+                else lon in lonWest..lonEast
+                if (isLonVisible) visibleSats.add(satellite to geoPos)
+            }
+        } else {
+            for (entry in posMap) visibleSats.add(entry.key to entry.value)
+        }
+
+        val showLabels = visibleSats.size <= LABEL_LIMIT
+        val activeNames = HashSet<String>(visibleSats.size)
+        for ((satellite, geoPos) in visibleSats) {
             val name = satellite.data.name
             activeNames.add(name)
             val marker = markerPool.getOrPut(name) {
                 Marker(mapView).apply {
                     setInfoWindow(null)
                     setAnchor(Marker.ANCHOR_CENTER, Marker.ANCHOR_CENTER)
-                    icon = getCachedTextIcon(name, mapView)
+                    // Resolve the satellite via relatedObject so the listener is allocated
+                    // once per marker instead of once per satellite per tick
+                    setOnMarkerClickListener { clicked, _ ->
+                        (clicked.relatedObject as? OrbitalObject)?.let(action)
+                        true
+                    }
                 }
             }
+            marker.relatedObject = satellite
+            val icon = if (showLabels) getCachedTextIcon(name, mapView) else getDotIcon(mapView)
+            if (marker.icon !== icon) marker.icon = icon
             // Update position in-place — reuse existing GeoPoint if available
             val pos = marker.position
             if (pos != null) {
@@ -775,22 +853,34 @@ private fun setPositions(
             } else {
                 marker.position = GeoPoint(geoPos.latitude, geoPos.longitude)
             }
-            marker.setOnMarkerClickListener { _, _ ->
-                action(satellite)
-                true
-            }
             folder.add(marker)
         }
-        // Evict markers for satellites no longer tracked
-        val iter = markerPool.keys.iterator()
-        while (iter.hasNext()) {
-            if (iter.next() !in activeNames) iter.remove()
-        }
+        // Evict markers that are no longer tracked or no longer visible
+        markerPool.keys.retainAll(activeNames)
+        visibleSats.clear()
     } catch (e: Exception) {
         println(e)
     }
 }
 
+/** Re-applies the last known positions against the new viewport after a pan or zoom */
+private fun refreshPositions(mapView: MapView): Boolean {
+    // Grid mode disables the satellite layer — don't re-populate markers off-screen
+    if (mapView.overlays.getOrNull(OVERLAY_POSITIONS)?.isEnabled == false) return true
+    val posMap = lastPositions ?: return false
+    val action = lastAction ?: return false
+    setPositions(posMap, mapView, action)
+    mapView.invalidate()
+    return true
+}
+
+private fun getDotIcon(mapView: MapView): Drawable = dotIcon ?: run {
+    val size = 20
+    val bitmap = createBitmap(size, size)
+    Canvas(bitmap).drawCircle(size / 2f, size / 2f, size / 2f - 2f, textPaint)
+    bitmap.toDrawable(mapView.context.resources).also { dotIcon = it }
+}
+
 private fun getCachedTextIcon(name: String, mapView: MapView): Drawable {
     iconCache[name]?.let { return it }
     val labelRect = Rect()
@@ -966,9 +1056,23 @@ private fun rememberMapViewWithLifecycle(): MapView {
         lifecycle.addObserver(lifecycleObserver)
         onDispose { lifecycle.removeObserver(lifecycleObserver) }
     }
+    // The overlay caches below are file-level (shared across MapView instances), so they must be
+    // released with the MapView or they keep the Activity and its bitmaps alive after disposal.
+    DisposableEffect(mapView) {
+        onDispose { clearMapCaches() }
+    }
     return mapView
 }
 
+private fun clearMapCaches() {
+    markerPool.clear()
+    iconCache.evictAll()
+    dotIcon = null
+    lastPositions = null
+    lastAction = null
+    lastMapView = null
+}
+
 @Composable
 private fun rememberMapViewLifecycleObserver(mapView: MapView) = remember(mapView) {
     LifecycleEventObserver { _, event ->

feature/map/src/main/java/com/rtbishop/look4sat/feature/map/MapState.kt

@@ -48,6 +48,7 @@ sealed interface MapAction {
     data class SelectItem(val item: OrbitalObject) : MapAction
     data class SelectDefaultItem(val catnum: Int) : MapAction
     data class ToggleGridMode(val value: Boolean) : MapAction
+    data class SetVisible(val isVisible: Boolean) : MapAction
 }
 
 data class MapData(

feature/map/src/main/java/com/rtbishop/look4sat/feature/map/MapViewModel.kt

@@ -37,6 +37,7 @@ import com.rtbishop.look4sat.core.domain.utility.toDegrees
 import com.rtbishop.look4sat.core.domain.utility.toTimerString
 import com.rtbishop.look4sat.core.presentation.getDefaultPass
 import kotlinx.coroutines.Job
+import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.async
 import kotlinx.coroutines.awaitAll
 import kotlinx.coroutines.cancelAndJoin
@@ -45,6 +46,7 @@ import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.collectLatest
+import kotlinx.coroutines.flow.first
 import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.isActive
 import kotlinx.coroutines.launch
@@ -69,6 +71,9 @@ class MapViewModel(
     private var dataUpdateJob: Job? = null
     private var dataUpdateRate = 1000L
     private var selectedOrbitalObject: OrbitalObject? = null
+
+    /** Gates the prediction loop so it doesn't burn CPU while the map isn't on screen */
+    private val isScreenVisible = MutableStateFlow(true)
     val uiState: StateFlow<MapState> = _uiState
 
     init {
@@ -100,6 +105,7 @@ class MapViewModel(
             is MapAction.SelectItem -> selectSatellite(action.item)
             is MapAction.SelectDefaultItem -> selectDefaultSatellite(action.catnum)
             is MapAction.ToggleGridMode -> settingsRepo.updateOtherSettings { it.copy(stateOfMapGrid = action.value) }
+            is MapAction.SetVisible -> isScreenVisible.value = action.isVisible
         }
     }
 
@@ -137,7 +143,11 @@ class MapViewModel(
         selectedOrbitalObject = orbitalObject
         viewModelScope.launch {
             dataUpdateJob?.cancelAndJoin()
-            dataUpdateJob = launch {
+            // Default dispatcher is mandatory: viewModelScope is Main.immediate, and every
+            // satelliteRepo call internally hops to Default and resumes back on the caller's
+            // dispatcher. On Main that posts one continuation per satellite per tick, which
+            // floods the looper and ANRs for users tracking thousands of objects.
+            dataUpdateJob = launch(Dispatchers.Default) {
                 val dateNow = Date()
                 getStationPosition()
                 getSatTrack(orbitalObject, stationPos, dateNow)
@@ -148,6 +158,8 @@ class MapViewModel(
                     else -> updateFreq
                 }
                 while (isActive) {
+                    // Suspends while the map is off-screen instead of predicting into the void
+                    isScreenVisible.first { it }
                     dateNow.time = System.currentTimeMillis()
                     updateMapState(orbitalObject, allSatellites, stationPos, dateNow)
                     delay(effectiveRate)