Hold-to-repeat for navigation keys across keyboard, gamepad and MIDI (v0.6.0)

Navigation and value-step actions (Nav Up/Down/Left/Right, Next/Prev
Column, Increment/Decrement) now auto-repeat while their control is held —
fire once on press, then accelerate from 320ms to 45ms per step — and stop
the instant it's released. Implemented ONCE as a shared repeater in
InputRouter (pressRepeat/releaseRepeat, keyed by the physical control id),
so all three hardware inputs get identical behaviour:
 * Keyboard: the OS's own key auto-repeat is now ignored (held notes sustain
   instead of retriggering) and holds are driven by the shared repeater;
   key-up ends it.
 * Gamepad: buttons, D-pad hat AND analog sticks repeat (they all funnel
   through controlDown/controlUp); releasing the main control stops it,
   releasing a chord modifier does not.
 * MIDI: a momentary nav CC repeats between its press (value>=64) and
   release (value<64).

One-shots (transport, tab switch, notes, clear) are unaffected — they fire
once even when held. InputRouter takes an injectable dispatcher so the new
InputRouterTest drives the accelerating schedule on a virtual clock
(verifies repeat-while-held, stop-on-release, one-shot-fires-once, and that
an unrelated release doesn't stop the active repeat). All unit tests pass;
on-device smoke confirms single-press nav + transport still work, no crash.

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

app/src/main/java/space/rcmd/android/sizzle/input/GamepadInput.kt

@@ -95,25 +95,28 @@ class GamepadInput(
             heldButtons.add(code)
             return true
         }
-        // Chord first: any already-held control may be the modifier.
+        // Chord first: any already-held control may be the modifier. Nav / value-step
+        // actions auto-repeat while held (keyed on the main control code); one-shots
+        // fire once. Held sticks and D-pad hats repeat too, since they arrive here.
         for (mod in heldButtons) {
             val id = bindings[GamepadChord(mod, code)]
             if (id != null) {
                 heldButtons.add(code)
-                InputActions.fromId(id)?.let { router.dispatch(it) }
+                InputActions.fromId(id)?.let { router.pressRepeat(code, it) }
                 return true
             }
         }
         heldButtons.add(code)
         // Otherwise the plain (no-modifier) binding.
         bindings[GamepadChord(GamepadChord.NONE, code)]?.let { id ->
-            InputActions.fromId(id)?.let { router.dispatch(it); return true }
+            InputActions.fromId(id)?.let { router.pressRepeat(code, it); return true }
         }
         return false
     }
 
     private fun controlUp(code: Int): Boolean {
         heldButtons.remove(code)
+        router.releaseRepeat(code) // end this control's hold-to-repeat, if any
         // Finalize a learn capture once every control in this combo is released.
         if (learningGamepad() && learnSeq.isNotEmpty() && heldButtons.none { it in learnSeq }) {
             val main = learnSeq.last()

app/src/main/java/space/rcmd/android/sizzle/input/InputAction.kt

@@ -62,3 +62,19 @@ sealed interface InputAction {
 
 /** Which physical device an action came from — handy for on-screen feedback. */
 enum class InputSource { TOUCH, KEYBOARD, GAMEPAD, MIDI }
+
+/**
+ * Actions that should AUTO-REPEAT while their physical control is held down —
+ * cursor movement, column movement and value stepping. Held via
+ * [InputRouter.pressRepeat], these fire once on press then accelerate. Everything
+ * else (transport, tab switch, note/clear) is a one-shot and fires only on press.
+ * Shared by all three hardware sources so hold-to-repeat feels identical on a
+ * keyboard, a gamepad and a MIDI controller.
+ */
+val InputAction.isRepeatable: Boolean
+    get() = when (this) {
+        InputAction.NavUp, InputAction.NavDown, InputAction.NavLeft, InputAction.NavRight,
+        InputAction.NextColumn, InputAction.PrevColumn,
+        is InputAction.Increment, is InputAction.Decrement -> true
+        else -> false
+    }

app/src/main/java/space/rcmd/android/sizzle/input/InputRouter.kt

@@ -3,9 +3,17 @@
 
 package space.rcmd.android.sizzle.input
 
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.MutableSharedFlow
 import kotlinx.coroutines.flow.SharedFlow
 import kotlinx.coroutines.flow.asSharedFlow
+import kotlinx.coroutines.isActive
+import kotlinx.coroutines.launch
 
 /**
  * A tiny message bus. Every input source calls [dispatch]; the app's ViewModel
@@ -16,7 +24,11 @@ import kotlinx.coroutines.flow.asSharedFlow
  * When "MIDI learn" mode is on, controls that aren't bound to anything are still
  * forwarded as [InputAction.RawControl] so the settings screen can capture them.
  */
-class InputRouter {
+class InputRouter(
+    /** Dispatcher the hold-to-repeat loop runs on. Defaults to a background pool;
+     *  tests inject a virtual-time dispatcher to drive the accelerating schedule. */
+    repeatDispatcher: CoroutineDispatcher = Dispatchers.Default,
+) {
     // extraBufferCapacity gives us headroom for fast MIDI/gamepad bursts.
     private val _actions = MutableSharedFlow<InputAction>(extraBufferCapacity = 128)
     val actions: SharedFlow<InputAction> = _actions.asSharedFlow()
@@ -33,4 +45,52 @@ class InputRouter {
         // oldest by design (a missed nav key is harmless, a stall is not).
         _actions.tryEmit(action)
     }
+
+    // ---- hold-to-repeat for navigation / value-step actions ----
+    // One accelerating repeater shared by every hardware source: a source calls
+    // [pressRepeat] when a control goes down and [releaseRepeat] when it comes up,
+    // keyed by that control's id. Only one repeat runs at a time (holding a new nav
+    // control replaces the old, which matches how you'd use it), so a single job is
+    // enough. Runs off the main thread; [dispatch] is thread-safe.
+    private val repeatScope = CoroutineScope(SupervisorJob() + repeatDispatcher)
+    @Volatile private var repeatJob: Job? = null
+    @Volatile private var repeatKey: Any? = null
+
+    /**
+     * Fire [action] once for a physical press and, if it [isRepeatable], keep
+     * re-firing it while held — after [REPEAT_START_MS], accelerating by
+     * [REPEAT_DECAY] each step down to [REPEAT_MIN_MS] — until [releaseRepeat] is
+     * called with the same [key]. [key] identifies the physical control (a key-code,
+     * a gamepad control code, a MIDI CC number) so the matching release stops it.
+     */
+    fun pressRepeat(key: Any, action: InputAction) {
+        dispatch(action)
+        if (!action.isRepeatable) return
+        repeatJob?.cancel()
+        repeatKey = key
+        repeatJob = repeatScope.launch {
+            var interval = REPEAT_START_MS
+            while (isActive) {
+                delay(interval)
+                dispatch(action)
+                interval = (interval * REPEAT_DECAY).toLong().coerceAtLeast(REPEAT_MIN_MS)
+            }
+        }
+    }
+
+    /** Stop the auto-repeat [pressRepeat] started for [key]. No-op if [key] isn't the
+     *  one currently repeating (e.g. releasing a modifier, or a non-repeating key). */
+    fun releaseRepeat(key: Any) {
+        if (repeatKey == key) {
+            repeatJob?.cancel()
+            repeatJob = null
+            repeatKey = null
+        }
+    }
+
+    companion object {
+        private const val REPEAT_START_MS = 320L   // initial hold before the first repeat
+        private const val REPEAT_MIN_MS = 45L      // fastest repeat once accelerated
+        private const val REPEAT_DECAY = 0.80      // interval shrink factor per repeat
+    }
 }

app/src/main/java/space/rcmd/android/sizzle/input/KeyboardInput.kt

@@ -47,13 +47,18 @@ class KeyboardInput(
 
     /** @return true if we consumed the event. */
     fun onKeyDown(keyCode: Int, event: KeyEvent): Boolean {
+        // Ignore the OS's own held-key auto-repeat (repeatCount > 0): note entry
+        // sustains until release, and hotkey hold-to-repeat is driven by our own
+        // accelerating repeater so it feels identical to the gamepad and MIDI.
+        if (event.repeatCount > 0) return bindings.containsKey(keyCode) || pianoMap.containsKey(keyCode)
+
         // Keyboard-hotkey learn: capture this key for the armed action, consume it.
         if (router.learnMode && router.learnSource == InputSource.KEYBOARD) {
             router.dispatch(InputAction.RawControl(InputSource.KEYBOARD, keyCode, 1f))
             return true
         }
 
-        bindings[keyCode]?.let { id -> return handleBoundAction(id, event) }
+        bindings[keyCode]?.let { id -> return handleBoundAction(id, keyCode, event) }
 
         // Piano fallback for unbound keys.
         pianoMap[keyCode]?.let { offset ->
@@ -64,24 +69,30 @@ class KeyboardInput(
     }
 
     /** Run a bound hotkey. Handles the keyboard-local ids (octave nudge, and the
-     *  Shift-aware column move) and delegates the rest to [InputActions]. */
-    private fun handleBoundAction(id: String, event: KeyEvent): Boolean {
+     *  Shift-aware column move) and delegates the rest to [InputActions]. Navigation /
+     *  value-step actions start a hold-to-repeat keyed on [keyCode] (ended in
+     *  [onKeyUp]); one-shots simply fire once. */
+    private fun handleBoundAction(id: String, keyCode: Int, event: KeyEvent): Boolean {
         when (id) {
             "octaveDown" -> baseOctave = (baseOctave - 1).coerceIn(0, 8)
             "octaveUp" -> baseOctave = (baseOctave + 1).coerceIn(0, 8)
             // The column key doubles as prev-column when Shift is held (classic Tab).
-            "nextColumn" -> router.dispatch(
+            "nextColumn" -> router.pressRepeat(
+                keyCode,
                 if (event.isShiftPressed) InputAction.PrevColumn else InputAction.NextColumn,
             )
             else -> {
                 val action = InputActions.fromId(id) ?: return false
-                router.dispatch(action)
+                router.pressRepeat(keyCode, action)
             }
         }
         return true
     }
 
     fun onKeyUp(keyCode: Int, @Suppress("UNUSED_PARAMETER") event: KeyEvent): Boolean {
+        // Stop any hold-to-repeat this key started (no-op for non-repeating keys).
+        router.releaseRepeat(keyCode)
+        if (bindings.containsKey(keyCode)) return true // consumed the bound hotkey
         val offset = pianoMap[keyCode] ?: return false
         router.dispatch(InputAction.NoteOff(pianoPitch(offset)))
         return true

app/src/main/java/space/rcmd/android/sizzle/input/MidiInput.kt

@@ -97,15 +97,26 @@ class MidiInput(
             router.dispatch(InputAction.RawControl(InputSource.MIDI, cc, value / 127f))
             return
         }
+        // Navigation CCs are momentary (a pad/note-button): press (value >= 64) starts
+        // an accelerating hold-to-repeat, release (value < 64) ends it — same feel as a
+        // held key or D-pad. Keyed on the CC number so its release stops the right one.
+        val nav = when (actionId) {
+            "up" -> InputAction.NavUp
+            "down" -> InputAction.NavDown
+            "left" -> InputAction.NavLeft
+            "right" -> InputAction.NavRight
+            else -> null
+        }
+        if (nav != null) {
+            if (value >= 64) router.pressRepeat(cc, nav) else router.releaseRepeat(cc)
+            return
+        }
+
         // Momentary controls fire on the "press" half (value >= 64).
         val action = when (actionId) {
             "playPause" -> if (value >= 64) InputAction.PlayPause else null
             "stop" -> if (value >= 64) InputAction.Stop else null
             "loop" -> if (value >= 64) InputAction.ToggleLoop else null
-            "up" -> if (value >= 64) InputAction.NavUp else null
-            "down" -> if (value >= 64) InputAction.NavDown else null
-            "left" -> if (value >= 64) InputAction.NavLeft else null
-            "right" -> if (value >= 64) InputAction.NavRight else null
             "increment" -> InputAction.Increment(1)
             "decrement" -> InputAction.Decrement(1)
             "clear" -> if (value >= 64) InputAction.ClearCell else null