keep the artwork transition animating when the base scheme changes

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

@@ -9,6 +9,7 @@ import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
+import androidx.compose.runtime.rememberUpdatedState
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.graphics.lerp
 import kotlin.math.roundToInt
@@ -40,21 +41,23 @@ fun rememberAnimatedArtworkColors(
 ): ArtworkColors {
     var from by remember { mutableStateOf(target ?: base) }
     var to by remember { mutableStateOf(target ?: base) }
+    var onBase by remember { mutableStateOf(target == null) }
     val progress = remember { Animatable(1f) }
+    val currentBase by rememberUpdatedState(base)
 
-    LaunchedEffect(target, base, durationMillis) {
-        val next = target ?: base
-        if (next !== to) {
-            if (to === base) {
-                from = next
-                to = next
-            } else {
-                from = lerpArtworkColors(from, to, progress.value)
-                to = next
-                progress.snapTo(0f)
-                progress.animateTo(1f, tween(durationMillis = durationMillis))
-            }
+    LaunchedEffect(target, durationMillis) {
+        val next = target ?: currentBase
+        if (next === to) return@LaunchedEffect
+        if (onBase) {
+            from = next
+            to = next
+        } else {
+            from = lerpArtworkColors(from, to, progress.value)
+            to = next
+            progress.snapTo(0f)
+            progress.animateTo(1f, tween(durationMillis = durationMillis))
         }
+        onBase = target == null
     }
 
     if (from === to) return to

app/src/test/kotlin/com/subtracks/ui/theme/ArtworkExtractionTest.kt

@@ -7,8 +7,10 @@ import androidx.activity.ComponentActivity
 import androidx.compose.material3.Text
 import androidx.compose.runtime.MutableState
 import androidx.compose.runtime.SideEffect
+import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
 import androidx.compose.ui.graphics.luminance
 import androidx.compose.ui.test.junit4.v2.createAndroidComposeRule
 import androidx.test.core.app.ApplicationProvider
@@ -89,6 +91,47 @@ class ArtworkExtractionTest {
         assertEquals(artworkColorsFromSeed(placeholderSeed("Kid A")).scheme.primary, colors?.scheme?.primary)
     }
 
+    @Test
+    fun fadesFromThePlaceholderToTheArtworkSeed() {
+        val placeholder = artworkColorsFromSeed(placeholderSeed("Kid A"))
+        val art = artworkColorsFromSeed(0xFF3A7BD5.toInt())
+        val artwork = mutableStateOf(placeholder)
+        val seen = mutableListOf<androidx.compose.ui.graphics.Color>()
+        composeRule.setContent {
+            SubtracksTheme {
+                val colors = rememberAnimatedArtworkColors(artwork.value, baseArtworkColors())
+                SideEffect { seen += colors.scheme.background }
+            }
+        }
+        composeRule.waitForIdle()
+        composeRule.runOnIdle { artwork.value = art }
+        composeRule.waitForIdle()
+        assertEquals(art.scheme.background, seen.last())
+    }
+
+    @Test
+    fun aChangingBaseSchemeDoesNotStrandTheArtworkTransition() {
+        val placeholder = artworkColorsFromSeed(placeholderSeed("Kid A"))
+        val art = artworkColorsFromSeed(0xFF3A7BD5.toInt())
+        val artwork = mutableStateOf(placeholder)
+        var baseTick by mutableStateOf(0)
+        val seen = mutableListOf<androidx.compose.ui.graphics.Color>()
+        composeRule.setContent {
+            SubtracksTheme {
+                val base = remember(baseTick) { artworkColorsFromSeed(baseTick) }
+                val colors = rememberAnimatedArtworkColors(artwork.value, base)
+                SideEffect {
+                    seen += colors.scheme.background
+                    if (artwork.value !== placeholder && baseTick < 20) baseTick++
+                }
+            }
+        }
+        composeRule.waitForIdle()
+        composeRule.runOnIdle { artwork.value = art }
+        composeRule.waitForIdle()
+        assertEquals(art.scheme.background, seen.last())
+    }
+
     @Test
     fun keepsContentStateWhenArtworkArrives() {
         val artwork = mutableStateOf<ArtworkColors?>(null)