Fix for imposible tile index crush.

src/commonMain/kotlin/centre/sciprog/maps/compose/MapTileProvider.kt

@@ -14,8 +14,6 @@ data class MapTile(
     val image: ImageBitmap,
 )
 
-
-
 interface MapTileProvider {
     suspend fun loadTile(id: TileId): MapTile
     fun toIndex(d: Double): Int = floor(d / DEFAULT_TILE_SIZE).toInt()

src/jvmMain/kotlin/Main.kt

@@ -13,32 +13,58 @@ import centre.sciprog.maps.MapViewPoint
 import centre.sciprog.maps.compose.*
 import io.ktor.client.HttpClient
 import io.ktor.client.engine.cio.CIO
+import kotlinx.coroutines.delay
 import java.nio.file.Path
+import kotlin.random.Random
+
+/**
+ *  initial set of features
+ */
+@Composable
+private fun initialFeatures() = buildList {
+    val pointOne = 55.568548 to 37.568604
+    val pointTwo = 55.929444 to 37.518434
+    add(MapVectorImageFeature(pointOne.toCoordinates(), Icons.Filled.Home))
+//            add(MapCircleFeature(pointOne))
+    add(MapCircleFeature(pointTwo))
+    add(MapLineFeature(pointOne, pointTwo))
+    add(MapTextFeature(pointOne.toCoordinates(), "Home"))
+}
+
 
 @Composable
 @Preview
 fun App() {
     MaterialTheme {
-        val viewPoint = MapViewPoint(
+        //create a view point
+        val viewPoint = remember {
+            MapViewPoint(
                 GeodeticMapCoordinates.ofDegrees(55.7558, 37.6173),
                 6.0
             )
-        val pointOne = 55.568548 to 37.568604
-        val pointTwo = 55.929444 to 37.518434
-        val features = buildList<MapFeature> {
-//            add(MapCircleFeature(pointOne))
-            add(MapCircleFeature(pointTwo))
-            add(MapLineFeature(pointOne, pointTwo))
-            add(MapTextFeature(pointOne.toCoordinates(), "Home"))
-            add(MapVectorImageFeature(pointOne.toCoordinates(), Icons.Filled.Home))
         }
 
+        // observable list of features
+        val features = mutableStateListOf<MapFeature>().apply {
+            addAll(initialFeatures())
+        }
+
+//        // test dynamic rendering
+//        LaunchedEffect(features) {
+//            repeat(10000) {
+//                delay(10)
+//                val randomPoint = Random.nextDouble(55.568548, 55.929444) to Random.nextDouble(37.518434, 37.568604)
+//                features.add(MapCircleFeature(randomPoint))
+//            }
+//        }
+
         val scope = rememberCoroutineScope()
         val mapTileProvider = remember { OpenStreetMapTileProvider(scope, HttpClient(CIO), Path.of("mapCache")) }
 
         var coordinates by remember { mutableStateOf<GeodeticMapCoordinates?>(null) }
 
         Column {
+            //display click coordinates
             Text(coordinates?.toString() ?: "")
             MapView(viewPoint, mapTileProvider, features = features) {
                 coordinates = it

src/jvmMain/kotlin/centre/sciprog/maps/compose/MapViewJvm.kt

@@ -36,7 +36,6 @@ private val logger = KotlinLogging.logger("MapView")
 /**
  * A component that renders map and provides basic map manipulation capabilities
  */
-@OptIn(ExperimentalComposeUiApi::class)
 @Composable
 actual fun MapView(
     initialViewPoint: MapViewPoint,
@@ -58,8 +57,6 @@ actual fun MapView(
 
     // Load tiles asynchronously
     LaunchedEffect(viewPoint, canvasSize) {
-        //remember zoom state to avoid races
-        val z = zoom
         val left = centerCoordinates.x - canvasSize.width / 2
         val right = centerCoordinates.x + canvasSize.width / 2
         val horizontalIndices = mapTileProvider.toIndex(left)..mapTileProvider.toIndex(right)
@@ -70,14 +67,18 @@ actual fun MapView(
 
         mapTiles.clear()
 
-        val indexRange = 0 until 2.0.pow(z).toInt()
+        val indexRange = 0 until 2.0.pow(zoom).toInt()
 
         for (j in verticalIndices) {
             for (i in horizontalIndices) {
-                if (z == zoom && i in indexRange && j in indexRange) {
+                if (i in indexRange && j in indexRange) {
-                    val tileId = TileId(z, i, j)
+                    val tileId = TileId(zoom, i, j)
+                    try {
                         val tile = mapTileProvider.loadTile(tileId)
                         mapTiles.add(tile)
+                    } catch (ex: Exception) {
+                        logger.error(ex) { "Failed to load tile $tileId" }
+                    }
                 }
             }
         }
@@ -99,6 +100,7 @@ actual fun MapView(
 
     fun GeodeticMapCoordinates.toOffset(): Offset = WebMercatorProjection.toMercator(this, zoom).toOffset()
 
+    @OptIn(ExperimentalComposeUiApi::class)
     val canvasModifier = modifier.onPointerEvent(PointerEventType.Press) {
         onClick(it.changes.first().position.toGeodetic())
     }.onPointerEvent(PointerEventType.Scroll) {

src/jvmMain/kotlin/centre/sciprog/maps/compose/OpenStreetMapTileProvider.kt

@@ -5,15 +5,13 @@ import androidx.compose.ui.graphics.toComposeImageBitmap
 import io.ktor.client.HttpClient
 import io.ktor.client.request.get
 import io.ktor.client.statement.readBytes
-import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.*
-import kotlinx.coroutines.Deferred
-import kotlinx.coroutines.Dispatchers
-import kotlinx.coroutines.async
 import mu.KotlinLogging
 import org.jetbrains.skia.Image
 import java.net.URL
 import java.nio.file.Path
 import kotlin.io.path.*
+import kotlin.math.pow
 
 /**
  * A [MapTileProvider] based on Open Street Map API. With in-memory and file cache
@@ -25,6 +23,9 @@ public class OpenStreetMapTileProvider(private val scope: CoroutineScope, privat
 
     private fun TileId.cacheFilePath() = cacheDirectory.resolve("${zoom}/${i}/${j}.png")
 
+    /**
+     * Download and cache the tile image
+     */
     private fun downloadImageAsync(id: TileId) = scope.async(Dispatchers.IO) {
         id.cacheFilePath()?.let { path ->
             if (path.exists()) {
@@ -53,6 +54,11 @@ public class OpenStreetMapTileProvider(private val scope: CoroutineScope, privat
     }
 
     override suspend fun loadTile(id: TileId): MapTile {
+        val indexRange = indexRange(id.zoom)
+        if(id.i !in indexRange || id.j !in indexRange){
+            error("Indices (${id.i}, ${id.j}) are not in index range $indexRange for zoom ${id.zoom}")
+        }
+
         val image = cache.getOrPut(id) {
             downloadImageAsync(id)
         }.await()
@@ -62,5 +68,6 @@ public class OpenStreetMapTileProvider(private val scope: CoroutineScope, privat
 
     companion object{
         private val logger = KotlinLogging.logger("OpenStreetMapCache")
+        private fun indexRange(zoom: Int): IntRange = 0 until 2.0.pow(zoom).toInt()
     }
 }