Merge branch 'claude/particle-wind-simulation-IMVxT' — Level 2 particle simulation

3 files changed, 171 insertions, 1 deletions

diff --git a/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt b/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
index 17fa52f..7046b23 100644
--- a/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
+++ b/android-app/app/src/main/kotlin/org/terst/nav/MainActivity.kt
@@ -37,6 +37,7 @@ import org.maplibre.android.style.sources.RasterSource
 import org.maplibre.android.style.sources.TileSet
 import org.terst.nav.ui.*
 import org.terst.nav.ui.doc.DocFragment
+import org.terst.nav.ui.map.ParticleWindView
 import org.terst.nav.ui.safety.SafetyFragment
 import org.terst.nav.ui.voicelog.VoiceLogFragment
 import java.util.*
@@ -51,6 +52,7 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
     private val loadedStyleFlow = MutableStateFlow<Style?>(null)
     private var weatherLoaded = false
     private var mapLibreMapRef: org.maplibre.android.maps.MapLibreMap? = null
+    private var particleWindView: ParticleWindView? = null
 
     private lateinit var bottomSheetBehavior: BottomSheetBehavior<View>
     private lateinit var fragmentContainer: FrameLayout
@@ -231,10 +233,12 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
 
     private fun setupMap() {
         mapView = findViewById(R.id.mapView)
+        particleWindView = findViewById(R.id.particle_wind_view)
         mapView?.onCreate(null)
         mapView?.getMapAsync { maplibreMap ->
             mapLibreMapRef = maplibreMap
             mapHandler = MapHandler(maplibreMap)
+            particleWindView?.attachMap(maplibreMap)
             val style = Style.Builder()
                 .fromUri("https://tiles.openfreemap.org/styles/liberty")
                 .withSource(RasterSource("openseamap-source",
@@ -277,7 +281,10 @@ class MainActivity : AppCompatActivity(), SafetyFragment.SafetyListener {
         }
         lifecycleScope.launch {
             viewModel.windArrow.collect { arrow ->
-                if (arrow != null) mapHandler?.updateWindLayer(arrow)
+                if (arrow != null) {
+                    mapHandler?.updateWindLayer(arrow)
+                    particleWindView?.setWind(arrow.directionDeg, arrow.speedKt)
+                }
             }
         }
         lifecycleScope.launch {
diff --git a/android-app/app/src/main/kotlin/org/terst/nav/ui/map/ParticleWindView.kt b/android-app/app/src/main/kotlin/org/terst/nav/ui/map/ParticleWindView.kt
new file mode 100644
index 0000000..0169fc1
--- /dev/null
+++ b/android-app/app/src/main/kotlin/org/terst/nav/ui/map/ParticleWindView.kt
@@ -0,0 +1,156 @@
+package org.terst.nav.ui.map
+
+import android.content.Context
+import android.graphics.Canvas
+import android.graphics.Color
+import android.graphics.Paint
+import android.util.AttributeSet
+import android.view.View
+import org.maplibre.android.geometry.LatLng
+import org.maplibre.android.maps.MapLibreMap
+import kotlin.math.cos
+import kotlin.math.sin
+import kotlin.random.Random
+
+/**
+ * Transparent canvas overlay that renders ~300 animated wind particles.
+ *
+ * Particle positions are tracked in lat/lon (FloatArray — no per-frame allocation).
+ * Each frame: project lat/lon → screen XY via MapLibreMap.projection, draw a short
+ * tail segment, then advance the position by the wind vector.
+ *
+ * Speed is scaled to the visible viewport so the animation looks consistent at any
+ * zoom level: a particle at reference wind (10 kt) crosses ~30% of the screen in
+ * MAX_AGE seconds.
+ */
+class ParticleWindView @JvmOverloads constructor(
+    context: Context,
+    attrs: AttributeSet? = null
+) : View(context, attrs) {
+
+    private var map: MapLibreMap? = null
+
+    /** Direction the wind is coming FROM, degrees true (meteorological convention). */
+    private var windDirFromDeg = 0.0
+    private var windSpeedKt = 0.0
+
+    private val N = 300
+    private val particleLat = FloatArray(N)
+    private val particleLon = FloatArray(N)
+    private val particleAge = FloatArray(N)
+    private val MAX_AGE = 8f   // seconds before forced respawn
+
+    private val paint = Paint(Paint.ANTI_ALIAS_FLAG).apply {
+        strokeWidth = 2.5f
+        strokeCap = Paint.Cap.ROUND
+        style = Paint.Style.STROKE
+    }
+
+    private var lastFrameNs = 0L
+    private var scattered = false
+
+    // ── Public API ──────────────────────────────────────────────────────────
+
+    fun attachMap(mapLibreMap: MapLibreMap) {
+        map = mapLibreMap
+        scattered = false
+    }
+
+    fun setWind(dirFromDeg: Double, speedKt: Double) {
+        windDirFromDeg = dirFromDeg
+        windSpeedKt = speedKt
+    }
+
+    // ── Rendering ────────────────────────────────────────────────────────────
+
+    override fun onDraw(canvas: Canvas) {
+        val m = map ?: run { postInvalidateOnAnimation(); return }
+
+        if (!scattered) scatter(m)
+
+        val now = System.nanoTime()
+        val dt = if (lastFrameNs == 0L) 0.016f
+                 else ((now - lastFrameNs) / 1_000_000_000f).coerceAtMost(0.05f)
+        lastFrameNs = now
+
+        val bounds = m.projection.visibleRegion.latLngBounds
+        val latSouth = bounds.latSouth.toFloat()
+        val latNorth = bounds.latNorth.toFloat()
+        val lonWest  = bounds.lonWest.toFloat()
+        val lonEast  = bounds.lonEast.toFloat()
+        val latRange = latNorth - latSouth
+        val lonRange = lonEast  - lonWest
+
+        // Speed scale: at 10kt a particle crosses 30% of viewport in MAX_AGE seconds.
+        val speedScale = latRange * 0.03f / MAX_AGE
+
+        // Geographic travel direction: opposite of the FROM direction.
+        val travelRad = Math.toRadians((windDirFromDeg + 180.0) % 360.0)
+        val cosTravel = cos(travelRad).toFloat()
+        val sinTravel = sin(travelRad).toFloat()
+
+        val dlat = cosTravel * windSpeedKt.toFloat() * speedScale * dt
+        val dlon = sinTravel * windSpeedKt.toFloat() * speedScale * dt
+
+        // Screen-space tail direction (accounts for map bearing).
+        val screenRad = travelRad - Math.toRadians(m.cameraPosition.bearing)
+        val tailDx = sin(screenRad).toFloat() * TAIL_PX
+        val tailDy = (-cos(screenRad)).toFloat() * TAIL_PX
+
+        for (i in 0 until N) {
+            particleLat[i] += dlat
+            particleLon[i] += dlon
+            particleAge[i] += dt
+
+            val needsRespawn = particleAge[i] > MAX_AGE
+                || particleLat[i] < latSouth || particleLat[i] > latNorth
+                || particleLon[i] < lonWest  || particleLon[i] > lonEast
+
+            if (needsRespawn) {
+                particleLat[i] = latSouth + Random.nextFloat() * latRange
+                particleLon[i] = lonWest  + Random.nextFloat() * lonRange
+                particleAge[i] = 0f
+                continue
+            }
+
+            val pt = m.projection.toScreenLocation(
+                LatLng(particleLat[i].toDouble(), particleLon[i].toDouble())
+            )
+
+            val alpha = ((1f - particleAge[i] / MAX_AGE) * 200).toInt().coerceIn(30, 200)
+            paint.color = Color.argb(alpha, 120, 200, 255)
+
+            canvas.drawLine(pt.x - tailDx, pt.y - tailDy, pt.x, pt.y, paint)
+        }
+
+        postInvalidateOnAnimation()
+    }
+
+    override fun onVisibilityChanged(changedView: View, visibility: Int) {
+        super.onVisibilityChanged(changedView, visibility)
+        if (visibility == VISIBLE) {
+            lastFrameNs = 0L
+            postInvalidateOnAnimation()
+        }
+    }
+
+    // ── Helpers ──────────────────────────────────────────────────────────────
+
+    private fun scatter(m: MapLibreMap) {
+        val bounds = m.projection.visibleRegion.latLngBounds
+        val latSouth = bounds.latSouth.toFloat()
+        val lonWest  = bounds.lonWest.toFloat()
+        val latRange = (bounds.latNorth - latSouth).toFloat()
+        val lonRange = (bounds.lonEast  - lonWest).toFloat()
+        for (i in 0 until N) {
+            particleLat[i] = latSouth + Random.nextFloat() * latRange
+            particleLon[i] = lonWest  + Random.nextFloat() * lonRange
+            particleAge[i] = Random.nextFloat() * MAX_AGE  // stagger so no mass respawn
+        }
+        scattered = true
+    }
+
+    companion object {
+        private const val TAIL_PX = 14f
+    }
+}
diff --git a/android-app/app/src/main/res/layout/activity_main.xml b/android-app/app/src/main/res/layout/activity_main.xml
index 68abc60..feeb43d 100644
--- a/android-app/app/src/main/res/layout/activity_main.xml
+++ b/android-app/app/src/main/res/layout/activity_main.xml
@@ -17,6 +17,13 @@
             android:layout_width="match_parent"
             android:layout_height="match_parent" />
 
+        <org.terst.nav.ui.map.ParticleWindView
+            android:id="@+id/particle_wind_view"
+            android:layout_width="match_parent"
+            android:layout_height="match_parent"
+            android:clickable="false"
+            android:focusable="false" />
+
         <!-- Overlay Fragment Container (for Log, Safety, Help) -->
         <FrameLayout
             android:id="@+id/fragment_container"