prefetch artwork seeds from the grid so an album opens with its theme

app/src/main/kotlin/com/subtracks/ui/library/AlbumsContent.kt

@@ -28,6 +28,7 @@ import com.subtracks.ui.components.CoverArt
 import com.subtracks.ui.components.EmptyState
 import com.subtracks.ui.components.LoadingState
 import com.subtracks.ui.components.rememberViewportFill
+import com.subtracks.ui.theme.PrefetchArtworkSeeds
 
 const val ALBUM_COVER_TAG = "album-cover"
 
@@ -62,8 +63,10 @@ fun AlbumsContent(
                 items(count = items.itemCount, key = items.itemKey { it.id }) { index ->
                     val album = items[index]
                     if (album != null) {
+                        val art = coverArt(album.coverArt, true)
+                        PrefetchArtworkSeeds(art)
                         CoverArt(
-                            ref = coverArt(album.coverArt, true),
+                            ref = art,
                             name = album.name,
                             modifier =
                                 Modifier

app/src/main/kotlin/com/subtracks/ui/library/ArtistDetailScreen.kt

@@ -53,6 +53,7 @@ import com.subtracks.data.model.Artist
 import com.subtracks.data.model.CoverArtRef
 import com.subtracks.ui.components.CoverArt
 import com.subtracks.ui.components.rememberViewportFill
+import com.subtracks.ui.theme.PrefetchArtworkSeeds
 import org.koin.compose.viewmodel.koinViewModel
 import org.koin.core.parameter.parametersOf
 
@@ -152,6 +153,7 @@ fun ArtistDetailScreen(
                 }
             }
             itemsIndexed(albums, key = { _, album -> album.id }) { index, album ->
+                PrefetchArtworkSeeds(coverArt(album.coverArt, true))
                 Column(
                     modifier =
                         Modifier

app/src/main/kotlin/com/subtracks/ui/theme/ArtworkSeedCache.kt

@@ -0,0 +1,113 @@
+package com.subtracks.ui.theme
+
+import android.content.Context
+import android.graphics.Bitmap
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.luminance
+import androidx.palette.graphics.Palette
+import coil3.SingletonImageLoader
+import coil3.compose.LocalPlatformContext
+import coil3.request.ImageRequest
+import coil3.request.SuccessResult
+import coil3.request.allowHardware
+import coil3.toBitmap
+import com.subtracks.data.model.CoverArtRef
+import kotlinx.coroutines.CancellationException
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Deferred
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.async
+import kotlinx.coroutines.delay
+import java.util.concurrent.ConcurrentHashMap
+import kotlin.math.abs
+
+private const val SEED_ART_SIZE_PX = 128
+private const val PREFETCH_SETTLE_MS = 250L
+
+object ArtworkSeedCache {
+    private val scope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
+    private val jobs = ConcurrentHashMap<String, Deferred<Pair<Int, Int?>?>>()
+
+    fun load(
+        context: Context,
+        ref: CoverArtRef,
+    ): Deferred<Pair<Int, Int?>?> =
+        jobs.getOrPut(ref.cacheKey) {
+            scope.async {
+                val seeds = extract(context, ref)
+                if (seeds == null) jobs.remove(ref.cacheKey)
+                seeds
+            }
+        }
+
+    private suspend fun extract(
+        context: Context,
+        ref: CoverArtRef,
+    ): Pair<Int, Int?>? =
+        try {
+            val request =
+                ImageRequest
+                    .Builder(context)
+                    .data(ref.url)
+                    .memoryCacheKey(ref.cacheKey)
+                    .diskCacheKey(ref.cacheKey)
+                    .size(SEED_ART_SIZE_PX)
+                    .allowHardware(false)
+                    .build()
+            val image = (SingletonImageLoader.get(context).execute(request) as? SuccessResult)?.image
+            image?.let { seedsFrom(it.toBitmap()) }
+        } catch (e: CancellationException) {
+            throw e
+        } catch (_: Exception) {
+            null
+        }
+
+    private fun seedsFrom(bitmap: Bitmap): Pair<Int, Int?>? {
+        val palette = Palette.from(bitmap).generate()
+        val primary =
+            palette.vibrantSwatch
+                ?: palette.lightVibrantSwatch
+                ?: palette.darkVibrantSwatch
+                ?: palette.mutedSwatch
+                ?: palette.dominantSwatch
+                ?: return null
+        val primaryColor = Color(primary.rgb or 0xFF000000.toInt())
+        val secondary =
+            listOfNotNull(
+                palette.vibrantSwatch,
+                palette.lightVibrantSwatch,
+                palette.darkVibrantSwatch,
+                palette.mutedSwatch,
+                palette.lightMutedSwatch,
+                palette.darkMutedSwatch,
+                palette.dominantSwatch,
+            ).map { it.rgb }
+                .distinct()
+                .filter { it != primary.rgb }
+                .maxByOrNull { distinctness(primaryColor, Color(it or 0xFF000000.toInt())) }
+        return primary.rgb to secondary
+    }
+
+    private fun distinctness(
+        a: Color,
+        b: Color,
+    ): Float {
+        val ha = a.toHsl().first
+        val hb = b.toHsl().first
+        val hueDistance = minOf(abs(ha - hb), 360f - abs(ha - hb)) / 180f
+        return hueDistance + abs(a.luminance() - b.luminance()) * 2f
+    }
+}
+
+@Composable
+fun PrefetchArtworkSeeds(ref: CoverArtRef?) {
+    val context = LocalPlatformContext.current
+    LaunchedEffect(ref?.cacheKey) {
+        if (ref == null) return@LaunchedEffect
+        delay(PREFETCH_SETTLE_MS)
+        ArtworkSeedCache.load(context, ref)
+    }
+}

app/src/main/kotlin/com/subtracks/ui/theme/ArtworkTheme.kt

@@ -1,6 +1,5 @@
 package com.subtracks.ui.theme
 
-import android.graphics.Bitmap
 import androidx.compose.foundation.Canvas
 import androidx.compose.material3.ColorScheme
 import androidx.compose.material3.MaterialTheme
@@ -17,21 +16,10 @@ import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.graphics.TileMode
 import androidx.compose.ui.graphics.lerp
 import androidx.compose.ui.graphics.luminance
-import androidx.palette.graphics.Palette
-import coil3.SingletonImageLoader
 import coil3.compose.LocalPlatformContext
-import coil3.request.ImageRequest
-import coil3.request.SuccessResult
-import coil3.request.allowHardware
-import coil3.toBitmap
 import com.subtracks.data.model.CoverArtRef
-import kotlinx.coroutines.CancellationException
-import kotlinx.coroutines.Dispatchers
-import kotlinx.coroutines.withContext
-import kotlin.math.abs
 import kotlin.random.Random
 
-private const val SEED_ART_SIZE_PX = 128
 private const val PERIOD_SCREENS = 2f
 private const val BLOB_ZONE = 0.62f
 private const val BLOB_COUNT = 4
@@ -185,67 +173,10 @@ fun rememberArtworkColors(
 private fun rememberArtworkSeed(ref: CoverArtRef?): State<Pair<Int, Int?>?> {
     val context = LocalPlatformContext.current
     return produceState<Pair<Int, Int?>?>(initialValue = null, ref?.cacheKey) {
-        value = null
+        value = ref?.let { ArtworkSeedCache.load(context, it).await() }
-        val art = ref ?: return@produceState
-        value =
-            withContext(Dispatchers.IO) {
-                try {
-                    val request =
-                        ImageRequest
-                            .Builder(context)
-                            .data(art.url)
-                            .memoryCacheKey(art.cacheKey)
-                            .diskCacheKey(art.cacheKey)
-                            .size(SEED_ART_SIZE_PX)
-                            .allowHardware(false)
-                            .build()
-                    val image = (SingletonImageLoader.get(context).execute(request) as? SuccessResult)?.image
-                    image?.let { seedsFrom(it.toBitmap()) }
-                } catch (e: CancellationException) {
-                    throw e
-                } catch (_: Exception) {
-                    null
-                }
-            }
     }
 }
 
-private fun seedsFrom(bitmap: Bitmap): Pair<Int, Int?>? {
-    val palette = Palette.from(bitmap).generate()
-    val primary =
-        palette.vibrantSwatch
-            ?: palette.lightVibrantSwatch
-            ?: palette.darkVibrantSwatch
-            ?: palette.mutedSwatch
-            ?: palette.dominantSwatch
-            ?: return null
-    val primaryColor = Color(primary.rgb or 0xFF000000.toInt())
-    val secondary =
-        listOfNotNull(
-            palette.vibrantSwatch,
-            palette.lightVibrantSwatch,
-            palette.darkVibrantSwatch,
-            palette.mutedSwatch,
-            palette.lightMutedSwatch,
-            palette.darkMutedSwatch,
-            palette.dominantSwatch,
-        ).map { it.rgb }
-            .distinct()
-            .filter { it != primary.rgb }
-            .maxByOrNull { distinctness(primaryColor, Color(it or 0xFF000000.toInt())) }
-    return primary.rgb to secondary
-}
-
-private fun distinctness(
-    a: Color,
-    b: Color,
-): Float {
-    val ha = a.toHsl().first
-    val hb = b.toHsl().first
-    val hueDistance = minOf(abs(ha - hb), 360f - abs(ha - hb)) / 180f
-    return hueDistance + abs(a.luminance() - b.luminance()) * 2f
-}
-
 @Composable
 fun ArtworkTheme(
     colors: ArtworkColors?,
@@ -340,7 +271,7 @@ fun heroDarkenAt(
     }
 }
 
-private fun Color.toHsl(): Triple<Float, Float, Float> {
+internal fun Color.toHsl(): Triple<Float, Float, Float> {
     val max = maxOf(red, green, blue)
     val min = minOf(red, green, blue)
     val lightness = (max + min) / 2f