align the artist top bar with the themed screens and scrim a busy name

- the artist top bar now uses the default app-bar title style and the art-derived
  heroBarColor instead of a hardcoded headline/black/white, so it follows the artist theme
- add a bottom scrim behind the overlaid artist name only when the art under it is bright
  or noisy, measured from the seed bitmap (so no extra decode)

app/src/test/kotlin/com/subtracks/ui/AppScreenshotTest.kt

@@ -40,6 +40,7 @@ import com.subtracks.playback.PlaybackState
 import com.subtracks.playback.QueueItem
 import com.subtracks.playback.RepeatMode
 import com.subtracks.ui.library.ALBUM_COVER_TAG
+import com.subtracks.ui.library.ARTIST_NAME_SCRIM_TAG
 import com.subtracks.ui.library.AlbumDetailScreen
 import com.subtracks.ui.library.ArtistDetailScreen
 import com.subtracks.ui.library.LibraryScreen
@@ -280,6 +281,9 @@ class AppScreenshotTest {
             }
         }
         awaitText("Kid A")
+        composeRule.waitUntil(timeoutMillis = 5_000) {
+            composeRule.onAllNodesWithTag(ARTIST_NAME_SCRIM_TAG).fetchSemanticsNodes().isNotEmpty()
+        }
         composeRule.onRoot().captureRoboImage("src/test/screenshots/artist_detail.png")
     }
 

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

@@ -0,0 +1,38 @@
+package com.subtracks.ui.theme
+
+import android.graphics.Bitmap
+import android.graphics.Color
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.annotation.GraphicsMode
+
+@RunWith(AndroidJUnit4::class)
+@GraphicsMode(GraphicsMode.Mode.NATIVE)
+class ArtworkNameBandTest {
+    private fun bitmap(bottom: (Int, Int) -> Int): Bitmap =
+        Bitmap.createBitmap(64, 64, Bitmap.Config.ARGB_8888).apply {
+            for (y in 0 until 64) {
+                for (x in 0 until 64) {
+                    setPixel(x, y, if (y >= 46) bottom(x, y) else Color.rgb(20, 20, 20))
+                }
+            }
+        }
+
+    @Test
+    fun darkCalmBandNeedsNoScrim() {
+        assertFalse(ArtworkSeedCache.bottomBandBusy(bitmap { _, _ -> Color.rgb(24, 20, 34) }))
+    }
+
+    @Test
+    fun brightBandNeedsAScrim() {
+        assertTrue(ArtworkSeedCache.bottomBandBusy(bitmap { _, _ -> Color.rgb(235, 230, 220) }))
+    }
+
+    @Test
+    fun noisyBandNeedsAScrim() {
+        assertTrue(ArtworkSeedCache.bottomBandBusy(bitmap { x, y -> if ((x + y) % 2 == 0) Color.WHITE else Color.BLACK }))
+    }
+}