Make mixer VU meters optional via a Settings toggle (v0.9.1)

Add a persisted "Mixer VU meters" switch (Settings -> Interface, on by default),
backed by a DataStore boolean. When off, the mixer skips the per-frame poll loop
entirely (the LaunchedEffect is keyed on the flag) and doesn't draw the meter, so
disabling it removes the metering cost, not just the visuals; the volume fill and
thumb render exactly as before.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/build.gradle.kts

@@ -22,8 +22,8 @@ android {
         // (android.media.midi) and AAudio low-latency audio we rely on.
         minSdk = 26
         targetSdk = 34
-        versionCode = 25
+        versionCode = 26
-        versionName = "0.9.0"
+        versionName = "0.9.1"
 
         // We provide our own instrumentation runner if/when tests are added.
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"

app/src/main/java/space/rcmd/android/sizzle/io/SettingsStore.kt

@@ -6,6 +6,7 @@ package space.rcmd.android.sizzle.io
 import android.content.Context
 import androidx.datastore.core.DataStore
 import androidx.datastore.preferences.core.Preferences
+import androidx.datastore.preferences.core.booleanPreferencesKey
 import androidx.datastore.preferences.core.edit
 import androidx.datastore.preferences.core.intPreferencesKey
 import androidx.datastore.preferences.core.stringPreferencesKey
@@ -26,6 +27,8 @@ data class AppSettings(
     val kbdChannel: Int = 0,
     /** Base octave for the on-screen keyboards. */
     val kbdOctave: Int = 3,
+    /** Show the live VU meters inside the mixer volume faders. */
+    val vuMeters: Boolean = true,
 )
 
 /**
@@ -47,6 +50,7 @@ class SettingsStore(private val context: Context) {
             recordTailBars = prefs[RECORD_TAIL] ?: 2,
             kbdChannel = prefs[KBD_CHANNEL] ?: 0,
             kbdOctave = prefs[KBD_OCTAVE] ?: 3,
+            vuMeters = prefs[VU_METERS] ?: true,
         )
     }
 
@@ -73,11 +77,17 @@ class SettingsStore(private val context: Context) {
         }
     }
 
+    /** Persist whether the mixer's fader VU meters are shown. */
+    suspend fun saveVuMeters(enabled: Boolean) {
+        context.settingsDataStore.edit { prefs -> prefs[VU_METERS] = enabled }
+    }
+
     private companion object {
         val PALETTE = stringPreferencesKey("palette")
         val RECORD_DIR = stringPreferencesKey("recordDirUri")
         val RECORD_TAIL = intPreferencesKey("recordTailBars")
         val KBD_CHANNEL = intPreferencesKey("kbdChannel")
         val KBD_OCTAVE = intPreferencesKey("kbdOctave")
+        val VU_METERS = booleanPreferencesKey("vuMeters")
     }
 }

app/src/main/java/space/rcmd/android/sizzle/ui/AppViewModel.kt

@@ -97,6 +97,15 @@ class AppViewModel(
     var kbdOctave by mutableIntStateOf(3); private set
     /** Velocity for keyboard notes (0..127). */
     var kbdVelocity by mutableIntStateOf(Cell.MAX_VELOCITY); private set
+    /** Whether the mixer's fader VU meters are shown (Settings toggle). */
+    var vuMeters by mutableStateOf(true); private set
+
+    /** Enable/disable the mixer fader VU meters and persist the choice. */
+    fun updateVuMeters(enabled: Boolean) {
+        vuMeters = enabled
+        viewModelScope.launch { settingsStore.saveVuMeters(enabled) }
+        touched()
+    }
 
     fun updateSkipStep(n: Int) { skipStep = n.coerceIn(0, 8) }
     fun togglePunchIn() { punchInMode = !punchInMode }
@@ -780,6 +789,7 @@ class AppViewModel(
             // Restore the on-screen keyboard's channel + octave.
             kbdChannel = s.kbdChannel.coerceIn(0, Cell.MAX_CHANNEL)
             kbdOctave = s.kbdOctave.coerceIn(0, 8)
+            vuMeters = s.vuMeters
             engine.recTempDir = appContext.cacheDir
             engine.setRecordTailBars(recordTailBars)
             engine.onRecordingStarted = {

app/src/main/java/space/rcmd/android/sizzle/ui/mixer/MixerScreen.kt

@@ -70,9 +70,16 @@ fun MixerScreen(vm: AppViewModel) {
     // stable state objects so only the fader's draw phase (which reads them) repaints —
     // the strips themselves never recompose from meter movement. Writing an unchanged
     // value is a no-op, so an idle (silent) mixer costs nothing but the frame tick.
+    // The whole poll loop is skipped when VU meters are turned off in Settings.
+    val vuOn = vm.vuMeters
     val levels = remember { List(Pattern.TRACK_COUNT) { mutableFloatStateOf(0f) } }
     val clips = remember { List(Pattern.TRACK_COUNT) { mutableStateOf(false) } }
-    LaunchedEffect(Unit) {
+    LaunchedEffect(vuOn) {
+        if (!vuOn) {
+            // Clear any lingering values so nothing shows if re-enabled while silent.
+            for (ch in 0 until Pattern.TRACK_COUNT) { levels[ch].floatValue = 0f; clips[ch].value = false }
+            return@LaunchedEffect
+        }
         while (true) {
             withFrameNanos { }
             for (ch in 0 until Pattern.TRACK_COUNT) {
@@ -89,7 +96,7 @@ fun MixerScreen(vm: AppViewModel) {
             horizontalArrangement = Arrangement.spacedBy(6.dp),
         ) {
             vm.project.mixer.channels.forEach { channel ->
-                ChannelStrip(vm, channel, levels[channel.index], clips[channel.index],
+                ChannelStrip(vm, channel, levels[channel.index], clips[channel.index], vuOn,
                     Modifier.weight(1f).fillMaxHeight())
             }
         }
@@ -157,6 +164,7 @@ private fun ChannelStrip(
     channel: MixerChannel,
     level: MutableFloatState,
     clipped: State<Boolean>,
+    showVu: Boolean,
     modifier: Modifier,
 ) {
     val c = LocalRetro.current
@@ -182,12 +190,12 @@ private fun ChannelStrip(
                 Column(
                     Modifier.weight(1f).fillMaxHeight(),
                     verticalArrangement = Arrangement.spacedBy(4.dp),
-                ) { ChannelLevels(vm, channel, level, clipped) }
+                ) { ChannelLevels(vm, channel, level, clipped, showVu) }
             }
         } else {
             // Portrait: one column, the fader filling the leftover height.
             ChannelRouting(vm, channel)
-            ChannelLevels(vm, channel, level, clipped)
+            ChannelLevels(vm, channel, level, clipped, showVu)
         }
     }
 }
@@ -244,6 +252,7 @@ private fun ColumnScope.ChannelLevels(
     channel: MixerChannel,
     level: MutableFloatState,
     clipped: State<Boolean>,
+    showVu: Boolean,
 ) {
     @Suppress("UNUSED_VARIABLE") val rev = vm.revision // defeat strong-skipping so LIM/mute/solo refresh
     SectionLabel("Volume")
@@ -253,6 +262,7 @@ private fun ColumnScope.ChannelLevels(
         onValueChange = { channel.volume = it; vm.bumpForToolbar() },
         level = level,
         clipped = clipped,
+        showVu = showVu,
         modifier = Modifier.weight(1f).fillMaxWidth(),
     )
     // Per-bus soft-clip limiter, sitting above mute/solo.
@@ -285,6 +295,7 @@ private fun VerticalFader(
     onValueChange: (Float) -> Unit,
     level: MutableFloatState,
     clipped: State<Boolean>,
+    showVu: Boolean,
     modifier: Modifier,
 ) {
     val c = LocalRetro.current
@@ -308,10 +319,11 @@ private fun VerticalFader(
                 // VU meter, contained within the fill. Colour maps to ABSOLUTE level
                 // over the full track height (bottom green → top red), so a taller bar
                 // is visibly hotter; the gradient's red tip is what "hard clipping turns
-                // to a red hue" looks like as the signal climbs.
+                // to a red hue" looks like as the signal climbs. Skipped when the VU
-                val lvl = level.floatValue.coerceIn(0f, 1f)
+                // meters are turned off in Settings.
+                val lvl = if (showVu) level.floatValue.coerceIn(0f, 1f) else 0f
                 val meterFrac = if (lvl < vol) lvl else vol // stay inside the filled area
-                if (meterFrac > 0.001f) {
+                if (showVu && meterFrac > 0.001f) {
                     val mH = meterFrac * h
                     val top = h - mH
                     if (clipped.value) {

app/src/main/java/space/rcmd/android/sizzle/ui/settings/SettingsScreen.kt

@@ -47,6 +47,7 @@ import androidx.compose.material3.ListItemDefaults
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.OutlinedButton
 import androidx.compose.material3.OutlinedTextField
+import androidx.compose.material3.Switch
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
 import androidx.compose.runtime.Composable
@@ -93,6 +94,7 @@ fun SettingsScreen(vm: AppViewModel) {
             item { PanicButton(vm) }
             item { ProjectCard(vm) }
             item { AudioDevicesCard(vm) }
+            item { InterfaceCard(vm) }
             item { ThemeCard(vm) }
             item {
                 NavCard("Gamepad Bindings", "Rebind buttons & combos", Icons.Filled.SportsEsports) {
@@ -368,6 +370,29 @@ private fun AudioDevicesCard(vm: AppViewModel) {
     }
 }
 
+/** Interface options: currently the mixer VU-meter toggle. */
+@Composable
+private fun InterfaceCard(vm: AppViewModel) {
+    @Suppress("UNUSED_VARIABLE") val rev = vm.revision // refresh the switch state
+    SettingsCard("Interface", subtitle = "On-screen display options") {
+        Row(
+            Modifier.fillMaxWidth(),
+            horizontalArrangement = Arrangement.SpaceBetween,
+            verticalAlignment = Alignment.CenterVertically,
+        ) {
+            Column(Modifier.weight(1f)) {
+                Text("Mixer VU meters", style = MaterialTheme.typography.bodyMedium)
+                Text(
+                    "Show live level meters inside the mixer volume faders.",
+                    style = MaterialTheme.typography.bodySmall,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant,
+                )
+            }
+            Switch(checked = vm.vuMeters, onCheckedChange = { vm.updateVuMeters(it) })
+        }
+    }
+}
+
 @Composable
 private fun ThemeCard(vm: AppViewModel) {
     val context = LocalContext.current