Async load

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

@@ -1,6 +1,7 @@
 package centre.sciprog.maps.compose
 
 import androidx.compose.ui.graphics.ImageBitmap
+import kotlinx.coroutines.Deferred
 import kotlin.math.floor
 
 data class TileId(
@@ -15,7 +16,7 @@ data class MapTile(
 )
 
 interface MapTileProvider {
-    suspend fun loadTile(id: TileId): MapTile
+    fun loadTileAsync(id: TileId): Deferred<MapTile>
 
     val tileSize: Int get() = DEFAULT_TILE_SIZE
 
@@ -27,3 +28,5 @@ interface MapTileProvider {
         const val DEFAULT_TILE_SIZE = 256
     }
 }
+
+suspend fun MapTileProvider.loadTile(id: TileId): MapTile = loadTileAsync(id).await()

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

@@ -17,6 +17,7 @@ import androidx.compose.ui.graphics.toArgb
 import androidx.compose.ui.input.pointer.*
 import androidx.compose.ui.unit.*
 import centre.sciprog.maps.*
+import kotlinx.coroutines.launch
 import mu.KotlinLogging
 import org.jetbrains.skia.Font
 import org.jetbrains.skia.Paint
@@ -149,8 +150,10 @@ actual fun MapView(
                 if (i in indexRange && j in indexRange) {
                     val tileId = TileId(zoom, i, j)
                     try {
-                        val tile = mapTileProvider.loadTile(tileId)
+                        launch {
-                        mapTiles.add(tile)
+                            val tile = mapTileProvider.loadTileAsync(tileId)
+                            mapTiles.add(tile.await())
+                        }
                     } catch (ex: Exception) {
                         logger.error(ex) { "Failed to load tile $tileId" }
                     }

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

@@ -5,7 +5,10 @@ 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.*
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Deferred
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.async
 import mu.KotlinLogging
 import org.jetbrains.skia.Image
 import java.net.URL
@@ -16,7 +19,11 @@ import kotlin.math.pow
 /**
  * A [MapTileProvider] based on Open Street Map API. With in-memory and file cache
  */
-public class OpenStreetMapTileProvider(private val scope: CoroutineScope, private val client: HttpClient, private val cacheDirectory: Path): MapTileProvider {
+public class OpenStreetMapTileProvider(
+    private val scope: CoroutineScope,
+    private val client: HttpClient,
+    private val cacheDirectory: Path,
+) : MapTileProvider {
     private val cache = HashMap<TileId, Deferred<ImageBitmap>>()
 
     private fun TileId.osmUrl() = URL("https://tile.openstreetmap.org/${zoom}/${i}/${j}.png")
@@ -53,20 +60,22 @@ public class OpenStreetMapTileProvider(private val scope: CoroutineScope, privat
         Image.makeFromEncoded(byteArray).toComposeImageBitmap()
     }
 
-    override suspend fun loadTile(id: TileId): MapTile {
+    override fun loadTileAsync(id: TileId): Deferred<MapTile> {
         val indexRange = indexRange(id.zoom)
-        if(id.i !in indexRange || id.j !in indexRange){
+        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()
+        }
 
-        return MapTile(id, image)
+        return scope.async {
+            MapTile(id, image.await())
+        }
     }
 
-    companion object{
+    companion object {
         private val logger = KotlinLogging.logger("OpenStreetMapCache")
         private fun indexRange(zoom: Int): IntRange = 0 until 2.0.pow(zoom).toInt()
     }