TTS improvements

composeApp/build.gradle.kts

@@ -3,7 +3,7 @@ import org.jetbrains.kotlin.gradle.ExperimentalWasmDsl
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
 
 val appVersionName = "1.1"
-val appVersionCode = 9
+val appVersionCode = 10
 val appVersionDisplay = "$appVersionName.$appVersionCode"
 
 plugins {

composeApp/src/androidMain/kotlin/net/sergeych/toread/BookPlatform.android.kt

@@ -485,6 +485,18 @@ actual suspend fun saveReaderFullScreen(fullScreen: Boolean) = withContext(Dispa
     }
 }
 
+actual suspend fun loadReaderPagingOnly(): Boolean = withContext(Dispatchers.IO) {
+    openLibraryDatabase().useLibrary { db ->
+        db.getAppFlag(ReaderPagingOnlyFlag)?.toBooleanStrictOrNull() ?: false
+    }
+}
+
+actual suspend fun saveReaderPagingOnly(enabled: Boolean) = withContext(Dispatchers.IO) {
+    openLibraryDatabase().useLibrary { db ->
+        db.setAppFlag(ReaderPagingOnlyFlag, enabled.toString())
+    }
+}
+
 actual suspend fun loadScanDownloadsAutomatically(): Boolean = withContext(Dispatchers.IO) {
     openLibraryDatabase().useLibrary { db ->
         db.getAppFlag(ScanDownloadsAutomaticallyFlag)?.toBooleanStrictOrNull() ?: true
@@ -904,6 +916,7 @@ private const val ActiveReadingFileIdFlag = "active_reading_file_id"
 private const val ThemeModeFlag = "theme_mode"
 private const val ReaderFontSettingsFlag = "reader_font_settings"
 private const val ReaderFullScreenFlag = "reader_full_screen"
+private const val ReaderPagingOnlyFlag = "reader_paging_only"
 private const val ScanDownloadsAutomaticallyFlag = "scan_downloads_automatically"
 private const val LibraryFilterFlag = "library_filter"
 private const val AppLocaleTagFlag = "app_locale_tag"

composeApp/src/androidMain/kotlin/net/sergeych/toread/ReadAloudPlatform.android.kt

@@ -15,6 +15,7 @@ import android.os.Bundle
 import android.os.IBinder
 import android.speech.tts.TextToSpeech
 import android.speech.tts.UtteranceProgressListener
+import android.util.Log
 import androidx.core.app.NotificationCompat
 import androidx.core.app.NotificationManagerCompat
 import androidx.core.content.ContextCompat
@@ -72,7 +73,6 @@ actual object ReadAloudPlatform {
 }
 
 private object AndroidReadAloudEngine {
-    private const val UtterancePrefix = "read-aloud-"
     private const val BeforePausePrefix = "read-aloud-before-"
     private const val SpeakPrefix = "read-aloud-speak-"
     private const val AfterPausePrefix = "read-aloud-after-"
@@ -97,13 +97,27 @@ private object AndroidReadAloudEngine {
     private var ttsEngineId: String? = null
     private var engineProbe: TextToSpeech? = null
     private var voiceProbe: TextToSpeech? = null
+    private var ttsGeneration = 0L
+    private var engineProbeGeneration = 0L
+    private var voiceProbeGeneration = 0L
     private var shouldSpeakWhenReady = false
     private var fileId: String? = null
     private var bookTitle: String = ""
     private var sentences: List<ReadAloudSentence> = emptyList()
     private var currentIndex: Int = 0
+    private var playbackGeneration = 0L
+    private var blockNumber = 0L
+    private var activeUtteranceId: String? = null
+    private var blocks: Iterator<ReadAloudBlock>? = null
+    private val queuedBlocks = linkedMapOf<String, ReadAloudBlock>()
 
+    private fun beforeId(id: String) = "$BeforePausePrefix$id"
+    private fun afterId(id: String) = "$AfterPausePrefix$id"
+
+    @Synchronized
     fun prepare(context: Context, fileId: String, title: String, queue: List<ReadAloudSentence>, startIndex: Int) {
+        shouldSpeakWhenReady = false
+        cancelQueue()
         this.fileId = fileId
         bookTitle = title
         sentences = queue
@@ -116,6 +130,7 @@ private object AndroidReadAloudEngine {
         ensureTts(context.applicationContext)
     }
 
+    @Synchronized
     fun play(context: Context) {
         if (sentences.isEmpty()) return
         ensureTts(context.applicationContext)
@@ -124,6 +139,7 @@ private object AndroidReadAloudEngine {
             mutableState.value = mutableState.value.copy(
                 active = true,
                 playing = true,
+                buffering = true,
                 sentenceIndex = sentences.getOrNull(currentIndex)?.index,
             )
             return
@@ -131,12 +147,14 @@ private object AndroidReadAloudEngine {
         speakCurrent()
     }
 
+    @Synchronized
     fun stop() {
         shouldSpeakWhenReady = false
-        tts?.stop()
+        cancelQueue()
         mutableState.value = ReadAloudState()
     }
 
+    @Synchronized
     fun skip(delta: Int) {
         if (sentences.isEmpty()) return
         val wasPlaying = mutableState.value.playing
@@ -153,51 +171,53 @@ private object AndroidReadAloudEngine {
         }
     }
 
+    @Synchronized
     fun refreshSettings(context: Context) {
         val appContext = context.applicationContext
-        val textReplacements = userTextReplacements(appContext)
         mutableSettingsState.value = mutableSettingsState.value.copy(
-            textReplacements = textReplacements,
+            textReplacements = userTextReplacements(appContext),
             loading = true,
             message = null,
         )
+        val generation = ++engineProbeGeneration
         engineProbe?.shutdown()
-        var probe: TextToSpeech? = null
-        probe = TextToSpeech(appContext) { status ->
+        engineProbe = TextToSpeech(appContext) { status ->
+            // Dispatch even if onInit fires synchronously inside the constructor.
+            scope.launch(Dispatchers.Main) { handleEngineProbeInit(appContext, generation, status) }
+        }
+    }
+
+    @Synchronized
+    private fun handleEngineProbeInit(context: Context, generation: Long, status: Int) {
+        if (generation != engineProbeGeneration) return
+        val probe = engineProbe ?: return
         if (status != TextToSpeech.SUCCESS) {
             mutableSettingsState.value = mutableSettingsState.value.copy(
-                    loading = false,
-                    message = strings.couldNotLoadAndroidTtsEngines,
+                loading = false, message = strings.couldNotLoadAndroidTtsEngines,
             )
-                probe?.shutdown()
-                if (engineProbe === probe) engineProbe = null
-                return@TextToSpeech
+            probe.shutdown()
+            engineProbe = null
+            return
         }
-
-            val engines = probe?.engines.orEmpty()
+        val engines = probe.engines.orEmpty()
             .map { ReadAloudEngineOption(id = it.name, label = it.label ?: it.name) }
             .sortedBy { it.label.lowercase() }
-            var selectedEngine = selectedEngineId(appContext).takeIf { saved ->
-                saved != null && engines.any { it.id == saved }
-            }
-            if (selectedEngine == null && !appContext.readAloudPrefs().getBoolean(EngineChoiceMadeKey, false)) {
+        var selectedEngine = selectedEngineId(context)
+        if (selectedEngine == null && !context.readAloudPrefs().getBoolean(EngineChoiceMadeKey, false)) {
             selectedEngine = engines.firstOrNull { it.isRhVoice() }?.id
             if (selectedEngine != null) {
-                    appContext.readAloudPrefs().edit().putString(SelectedEngineKey, selectedEngine).apply()
+                context.readAloudPrefs().edit().putString(SelectedEngineKey, selectedEngine).apply()
             }
         }
         mutableSettingsState.value = mutableSettingsState.value.copy(
-                engines = engines,
-                selectedEngineId = selectedEngine,
-                textReplacements = textReplacements,
+            engines = engines, selectedEngineId = selectedEngine,
         )
-            probe?.shutdown()
-            if (engineProbe === probe) engineProbe = null
-            refreshVoices(appContext, selectedEngine)
-        }
-        engineProbe = probe
+        probe.shutdown()
+        engineProbe = null
+        refreshVoices(context, selectedEngine)
     }
 
+    @Synchronized
     fun selectEngine(context: Context, engineId: String?) {
         val appContext = context.applicationContext
         appContext.readAloudPrefs()
@@ -206,6 +226,7 @@ private object AndroidReadAloudEngine {
             .putStringOrRemove(SelectedEngineKey, engineId)
             .remove(SelectedVoiceKey)
             .apply()
+        val wasPlaying = mutableState.value.playing
         resetTts()
         mutableSettingsState.value = mutableSettingsState.value.copy(
             selectedEngineId = engineId,
@@ -215,8 +236,10 @@ private object AndroidReadAloudEngine {
             message = null,
         )
         refreshVoices(appContext, engineId)
+        if (wasPlaying) play(appContext)
     }
 
+    @Synchronized
     fun selectVoice(context: Context, voiceId: String?) {
         val appContext = context.applicationContext
         appContext.readAloudPrefs()
@@ -236,25 +259,35 @@ private object AndroidReadAloudEngine {
         if (tts != null && ttsEngineId == selectedEngine) return
         resetTts()
         ttsEngineId = selectedEngine
+        val generation = ttsGeneration
         tts = if (selectedEngine == null) {
             TextToSpeech(appContext) { status ->
-                handleTtsInit(appContext, status)
+                scope.launch(Dispatchers.Main) { handleTtsInit(appContext, generation, status) }
             }
         } else {
             TextToSpeech(
                 appContext,
-                { status -> handleTtsInit(appContext, status) },
+                { status -> scope.launch(Dispatchers.Main) { handleTtsInit(appContext, generation, status) } },
                 selectedEngine,
             )
         }
     }
 
-    private fun handleTtsInit(context: Context, status: Int) {
+    @Synchronized
+    private fun handleTtsInit(context: Context, generation: Long, status: Int) {
+        if (generation != ttsGeneration) return
         ttsReady = status == TextToSpeech.SUCCESS
         if (ttsReady) {
             applyTtsConfiguration(context)
+            Log.i("YereedTts", "Initialized requested engine=${ttsEngineId ?: "system default"}, voice=${tts?.voice?.name}")
             tts?.setOnUtteranceProgressListener(object : UtteranceProgressListener() {
-                override fun onStart(utteranceId: String?) = Unit
+                override fun onStart(utteranceId: String?) {
+                    handleUtteranceStart(utteranceId)
+                }
+
+                override fun onRangeStart(utteranceId: String?, start: Int, end: Int, frame: Int) {
+                    handleUtteranceRange(utteranceId, start)
+                }
 
                 override fun onDone(utteranceId: String?) {
                     handleUtteranceDone(utteranceId)
@@ -262,11 +295,11 @@ private object AndroidReadAloudEngine {
 
                 @Deprecated("Deprecated in Java")
                 override fun onError(utteranceId: String?) {
-                    stop()
+                    handleUtteranceError(utteranceId)
                 }
 
                 override fun onError(utteranceId: String?, errorCode: Int) {
-                    stop()
+                    handleUtteranceError(utteranceId)
                 }
             })
             if (shouldSpeakWhenReady) {
@@ -278,51 +311,94 @@ private object AndroidReadAloudEngine {
         }
     }
 
+    private fun cancelQueue() {
+        // Invalidate callbacks before stopping: a late event must not affect the new queue.
+        playbackGeneration++
+        blocks = null
+        activeUtteranceId = null
+        queuedBlocks.clear()
+        tts?.stop()
+    }
+
     private fun speakCurrent() {
         val sentence = sentences.getOrNull(currentIndex) ?: run {
             stop()
             return
         }
+        cancelQueue()
         mutableState.value = ReadAloudState(active = true, playing = true, sentenceIndex = sentence.index)
         saveSentencePosition(sentence)
-        val params = Bundle().apply {
-            putString(TextToSpeech.Engine.KEY_PARAM_UTTERANCE_ID, "$SpeakPrefix$currentIndex")
-        }
-        val queueMode = if (sentence.pauseBeforeMillis > 0) {
-            tts?.playSilentUtterance(sentence.pauseBeforeMillis, TextToSpeech.QUEUE_FLUSH, "$BeforePausePrefix$currentIndex")
-            TextToSpeech.QUEUE_ADD
-        } else {
-            TextToSpeech.QUEUE_FLUSH
-        }
-        tts?.speak(sentence.spokenText, queueMode, params, "$SpeakPrefix$currentIndex")
-        if (sentence.pauseAfterMillis > 0) {
-            tts?.playSilentUtterance(sentence.pauseAfterMillis, TextToSpeech.QUEUE_ADD, "$AfterPausePrefix$currentIndex")
-        }
+        blocks = readAloudBlocks(
+            sentences, currentIndex, minOf(4_000, TextToSpeech.getMaxSpeechInputLength()),
+        ).iterator()
+        fillQueue()
     }
 
-    private fun handleUtteranceDone(utteranceId: String?) {
+    private fun fillQueue() {
+        val engine = tts ?: return
+        val remaining = blocks ?: return
+        // Keep the current block and two successors submitted, before playback ends.
+        while (queuedBlocks.size < 3 && remaining.hasNext()) {
+            val block = remaining.next()
+            val id = "$SpeakPrefix$playbackGeneration-${blockNumber++}"
+            queuedBlocks[id] = block
+            val beforeResult = if (block.pauseBeforeMillis > 0) {
+                engine.playSilentUtterance(block.pauseBeforeMillis, TextToSpeech.QUEUE_ADD, beforeId(id))
+            } else TextToSpeech.SUCCESS
+            val speechResult = engine.speak(block.text, TextToSpeech.QUEUE_ADD, Bundle(), id)
+            val afterResult = if (block.pauseAfterMillis > 0) {
+                engine.playSilentUtterance(block.pauseAfterMillis, TextToSpeech.QUEUE_ADD, afterId(id))
+            } else TextToSpeech.SUCCESS
+            if (beforeResult == TextToSpeech.ERROR || speechResult == TextToSpeech.ERROR ||
+                afterResult == TextToSpeech.ERROR) {
+                stop()
+                return
+            }
+        }
+        if (queuedBlocks.isEmpty()) stop()
+    }
+
+    private fun updatePosition(position: Int) {
+        if (currentIndex == position && mutableState.value.sentenceIndex == sentences[position].index) return
+        currentIndex = position
+        val sentence = sentences[position]
+        mutableState.value = mutableState.value.copy(sentenceIndex = sentence.index)
+        saveSentencePosition(sentence)
+    }
+
+    @Synchronized
+    private fun handleUtteranceStart(utteranceId: String?) {
         if (!mutableState.value.playing) return
-        val speakIndex = utteranceId?.removePrefix(SpeakPrefix)?.takeIf { it != utteranceId }?.toIntOrNull()
-        val afterIndex = utteranceId?.removePrefix(AfterPausePrefix)?.takeIf { it != utteranceId }?.toIntOrNull()
-        val finishedIndex = afterIndex ?: speakIndex ?: return
-        if (finishedIndex != currentIndex) return
-        val currentSentence = sentences.getOrNull(currentIndex) ?: run {
-            stop()
-            return
+        val block = queuedBlocks[utteranceId] ?: return
+        activeUtteranceId = utteranceId
+        updatePosition(block.ranges.first().position)
     }
-        if (speakIndex != null && currentSentence.pauseAfterMillis > 0) {
-            sentences.getOrNull(currentIndex + 1)?.let { nextSentence ->
-                mutableState.value = mutableState.value.copy(sentenceIndex = nextSentence.index)
-                saveSentencePosition(nextSentence)
+
+    @Synchronized
+    private fun handleUtteranceRange(utteranceId: String?, offset: Int) {
+        if (!mutableState.value.playing || utteranceId != activeUtteranceId) return
+        val block = queuedBlocks[utteranceId] ?: return
+        updatePosition(block.positionAt(offset))
     }
-            return
+
+    @Synchronized
+    private fun handleUtteranceDone(utteranceId: String?) {
+        if (!mutableState.value.playing || utteranceId == null) return
+        val isAfter = utteranceId.startsWith(AfterPausePrefix)
+        val id = if (isAfter) utteranceId.removePrefix(AfterPausePrefix) else utteranceId
+        val block = queuedBlocks[id] ?: return
+        if (!isAfter) {
+            if (activeUtteranceId == id) updatePosition(block.ranges.last().position)
+            if (block.pauseAfterMillis > 0) return
         }
-        if (currentIndex < sentences.lastIndex) {
-            currentIndex += 1
-            speakCurrent()
-        } else {
-            stop()
+        queuedBlocks.remove(id)
+        fillQueue()
     }
+
+    @Synchronized
+    private fun handleUtteranceError(utteranceId: String?) {
+        val id = utteranceId?.removePrefix(BeforePausePrefix)?.removePrefix(AfterPausePrefix)
+        if (queuedBlocks.containsKey(id)) stop()
     }
 
     fun notificationTitle(): String = bookTitle.ifBlank { strings.readAloud }
@@ -341,34 +417,28 @@ private object AndroidReadAloudEngine {
     }
 
     private fun refreshVoices(context: Context, engineId: String?) {
+        val generation = ++voiceProbeGeneration
         voiceProbe?.shutdown()
-        var probe: TextToSpeech? = null
-        probe = if (engineId == null) {
-            TextToSpeech(context) { status ->
-                handleVoiceProbeInit(context, probe, status)
-            }
-        } else {
-            TextToSpeech(
-                context,
-                { status -> handleVoiceProbeInit(context, probe, status) },
-                engineId,
-            )
-        }
-        voiceProbe = probe
+        voiceProbe = TextToSpeech(context, { status ->
+            scope.launch(Dispatchers.Main) { handleVoiceProbeInit(context, generation, status) }
+        }, engineId)
     }
 
-    private fun handleVoiceProbeInit(context: Context, probe: TextToSpeech?, status: Int) {
+    @Synchronized
+    private fun handleVoiceProbeInit(context: Context, generation: Long, status: Int) {
+        if (generation != voiceProbeGeneration) return
+        val probe = voiceProbe ?: return
         if (status != TextToSpeech.SUCCESS) {
             mutableSettingsState.value = mutableSettingsState.value.copy(
                 loading = false,
                 message = strings.couldNotLoadSelectedTtsVoices,
             )
-            probe?.shutdown()
+            probe.shutdown()
             if (voiceProbe === probe) voiceProbe = null
             return
         }
 
-        val voices = probe?.voices.orEmpty()
+        val voices = probe.voices.orEmpty()
             .mapNotNull { voice ->
                 val locale = voice.locale ?: return@mapNotNull null
                 ReadAloudVoiceOption(
@@ -396,7 +466,7 @@ private object AndroidReadAloudEngine {
         if (savedVoice == null && selectedVoiceId(context) != null) {
             context.readAloudPrefs().edit().remove(SelectedVoiceKey).apply()
         }
-        probe?.shutdown()
+        probe.shutdown()
         if (voiceProbe === probe) voiceProbe = null
     }
 
@@ -413,10 +483,11 @@ private object AndroidReadAloudEngine {
     }
 
     private fun resetTts() {
+        ttsGeneration++
         shouldSpeakWhenReady = false
         ttsReady = false
         ttsEngineId = null
-        tts?.stop()
+        cancelQueue()
         tts?.shutdown()
         tts = null
     }

composeApp/src/commonMain/kotlin/net/sergeych/toread/LibraryPlatform.kt

@@ -171,6 +171,10 @@ expect suspend fun loadReaderFullScreen(): Boolean
 
 expect suspend fun saveReaderFullScreen(fullScreen: Boolean)
 
+expect suspend fun loadReaderPagingOnly(): Boolean
+
+expect suspend fun saveReaderPagingOnly(enabled: Boolean)
+
 expect suspend fun loadScanDownloadsAutomatically(): Boolean
 
 expect suspend fun saveScanDownloadsAutomatically(enabled: Boolean)

composeApp/src/commonMain/kotlin/net/sergeych/toread/Localization.kt

@@ -160,6 +160,7 @@ internal open class AppStrings {
     open val readerTypography = "Typography"
     open val readerLayout = "Layout"
     open val readerNavigation = "Navigation"
+    open val readerPagingOnly = "Paging only (no free scroll)"
     open val readerProgress = "Progress"
     open val closeReaderSettings = "Close reader settings"
     open val share = "Share"
@@ -388,6 +389,7 @@ internal object RussianStrings : AppStrings() {
     override val readerTypography = "Типографика"
     override val readerLayout = "Макет"
     override val readerNavigation = "Навигация"
+    override val readerPagingOnly = "Постраничный режим (без прокрутки)"
     override val readerProgress = "Прогресс"
     override val closeReaderSettings = "Закрыть настройки чтения"
     override val share = "Поделиться"

composeApp/src/commonMain/kotlin/net/sergeych/toread/ReadAloudBlocks.kt

@@ -0,0 +1,67 @@
+package net.sergeych.toread
+
+internal data class ReadAloudBlockRange(val position: Int, val start: Int, val endExclusive: Int)
+
+internal data class ReadAloudBlock(
+    val text: String,
+    val ranges: List<ReadAloudBlockRange>,
+    val pauseBeforeMillis: Long,
+    val pauseAfterMillis: Long,
+) {
+    fun positionAt(offset: Int): Int =
+        ranges.lastOrNull { it.start <= offset }?.position ?: ranges.first().position
+}
+
+/** Paragraph-sized requests. Android's hard limit counts UTF-16 characters, never UTF-8 bytes.
+ * Whole sentences are retained whenever they fit. An oversized sentence is split at whitespace,
+ * or, for an oversized word, between Unicode code points (never inside a surrogate pair).
+ */
+internal fun readAloudBlocks(
+    sentences: List<ReadAloudSentence>,
+    startIndex: Int,
+    maxLength: Int,
+): Sequence<ReadAloudBlock> = sequence {
+    require(maxLength >= 2)
+    var text = StringBuilder()
+    var ranges = mutableListOf<ReadAloudBlockRange>()
+    var before = 0L
+    var after = 0L
+    var item: Int? = null
+
+    suspend fun SequenceScope<ReadAloudBlock>.flush() {
+        if (ranges.isEmpty()) return
+        yield(ReadAloudBlock(text.toString(), ranges.toList(), before, after))
+        text = StringBuilder()
+        ranges = mutableListOf()
+        before = 0L
+        after = 0L
+    }
+
+    for (position in startIndex.coerceAtLeast(0) until sentences.size) {
+        val sentence = sentences[position]
+        if (item != sentence.itemIndex || sentence.pauseBeforeMillis > 0 || after > 0) flush()
+        item = sentence.itemIndex
+        var offset = 0
+        val spoken = sentence.spokenText
+        while (offset < spoken.length) {
+            // Do not split a sentence just to fill the previous block.
+            if (text.isNotEmpty() && text.length + 1 + spoken.length - offset > maxLength) flush()
+            if (ranges.isEmpty()) before = if (offset == 0) sentence.pauseBeforeMillis else 0L
+            var end = minOf(spoken.length, offset + maxLength)
+            if (end < spoken.length) {
+                if (spoken[end - 1].isHighSurrogate() && spoken[end].isLowSurrogate()) end--
+                val whitespace = (end - 1 downTo offset + 1).firstOrNull { spoken[it].isWhitespace() }
+                if (whitespace != null) end = whitespace
+            }
+            if (text.isNotEmpty()) text.append(' ')
+            val start = text.length
+            text.append(spoken.substring(offset, end))
+            ranges += ReadAloudBlockRange(position, start, text.length)
+            offset = end
+            while (offset < spoken.length && spoken[offset].isWhitespace()) offset++
+            after = if (offset == spoken.length) sentence.pauseAfterMillis else 0L
+            if (offset < spoken.length || text.length >= maxLength || after > 0) flush()
+        }
+    }
+    flush()
+}

composeApp/src/commonMain/kotlin/net/sergeych/toread/ReaderContent.kt

@@ -59,6 +59,7 @@ import androidx.compose.ui.graphics.ImageBitmap
 import androidx.compose.ui.graphics.StrokeCap
 import androidx.compose.ui.graphics.graphicsLayer
 import androidx.compose.ui.input.pointer.PointerEventPass
+import androidx.compose.ui.input.pointer.PointerEventType
 import androidx.compose.ui.input.pointer.PointerType
 import androidx.compose.ui.input.pointer.pointerInput
 import androidx.compose.ui.layout.ContentScale
@@ -127,6 +128,7 @@ internal fun ContinuousBookReader(
     readerFontSettings: ReaderFontSettings = defaultReaderFontSettings(),
     readerBackgroundColor: Color = MaterialTheme.colorScheme.surface,
     readerTextColor: Color = MaterialTheme.colorScheme.onSurface,
+    pagingOnly: Boolean = false,
     onReaderFontZoom: (Int) -> Unit = {},
     onUserScroll: () -> Unit = {},
     onImageOpen: (ViewedBookImage) -> Unit = {},
@@ -153,6 +155,7 @@ internal fun ContinuousBookReader(
         modifier = modifier
             .background(readerBackgroundColor)
             .nestedScroll(userScrollConnection)
+            .blockFreeScroll(pagingOnly)
             .readerFontZoomGesture(onReaderFontZoom)
             .pageTurnOnTouchSwipe(
                 onPageDown = {
@@ -213,7 +216,6 @@ internal fun ContinuousBookReader(
                         )
                         .padding(
                             top = if (element.depth == 0) 22.dp else 14.dp,
-                            start = (element.depth * 12).dp,
                             bottom = 4.dp,
                         )
                     Text(
@@ -242,7 +244,6 @@ internal fun ContinuousBookReader(
                     style = readerParagraphTextStyle(book.language, readerFontSettings).copy(color = readerTextColor),
                     highlightedRange = highlightedRange,
                     textAlign = TextAlign.Justify,
-                    modifier = Modifier.padding(start = (element.depth * 8).dp, end = 0.dp),
                     onTextLayout = { textLineMetricsByItem[itemIndex] = it.toTextLineMetrics() },
                     onLinkOpen = onNoteOpen,
                 )
@@ -333,6 +334,43 @@ private fun List<androidx.compose.ui.input.pointer.PointerInputChange>.firstTwoD
     return sqrt(dx * dx + dy * dy)
 }
 
+/**
+ * Consumes vertical touch drags and mouse wheel/trackpad scroll so the lazy list
+ * cannot be scrolled freely ("paging only" mode). Taps and horizontal swipes are
+ * left untouched so page-turn gestures and clickable items keep working.
+ */
+private fun Modifier.blockFreeScroll(enabled: Boolean): Modifier =
+    if (!enabled) {
+        this
+    } else {
+        pointerInput(Unit) {
+            awaitEachGesture {
+                val down = awaitFirstDown(requireUnconsumed = false, pass = PointerEventPass.Initial)
+                if (down.isConsumed) return@awaitEachGesture
+                val touchSlop = viewConfiguration.touchSlop
+                val touchSlopSquared = touchSlop * touchSlop
+                var verticalDragLocked = false
+                while (true) {
+                    val event = awaitPointerEvent(pass = PointerEventPass.Initial)
+                    if (event.type == PointerEventType.Scroll) {
+                        event.changes.forEach { it.consume() }
+                        continue
+                    }
+                    val change = event.changes.firstOrNull { it.id == down.id } ?: break
+                    if (!change.pressed) break
+                    if (!verticalDragLocked) {
+                        val dx = change.position.x - down.position.x
+                        val dy = change.position.y - down.position.y
+                        if (dy * dy > touchSlopSquared && dy * dy > ReaderHorizontalSwipeDominance * dx * dx) {
+                            verticalDragLocked = true
+                        }
+                    }
+                    if (verticalDragLocked) change.consume()
+                }
+            }
+        }
+    }
+
 private fun Modifier.pageTurnOnTouchSwipe(
     onPageDown: () -> Unit,
     onPageUp: () -> Unit,
@@ -953,7 +991,7 @@ private fun ReaderPoem(
     Column(
         modifier = modifier
             .fillMaxWidth()
-            .padding(start = (depth * 8).dp, top = 8.dp, bottom = 8.dp),
+            .padding(top = 8.dp, bottom = 8.dp),
     ) {
         poem.epigraphs.forEachIndexed { index, epigraph ->
             ReaderEpigraph(
@@ -1008,7 +1046,7 @@ private fun ReaderEpigraph(
     Column(
         modifier = modifier
             .fillMaxWidth()
-            .padding(start = (depth * 8 + 26).dp, end = 18.dp, top = 8.dp, bottom = 8.dp),
+            .padding(start = 26.dp, end = 18.dp, top = 8.dp, bottom = 8.dp),
         verticalArrangement = Arrangement.spacedBy(6.dp),
     ) {
         epigraph.blocks.forEach { block ->
@@ -1051,7 +1089,7 @@ private fun ReaderCite(
     Column(
         modifier = modifier
             .fillMaxWidth()
-            .padding(start = (depth * 8 + 22).dp, end = 14.dp, top = 8.dp, bottom = 8.dp),
+            .padding(start = 22.dp, end = 14.dp, top = 8.dp, bottom = 8.dp),
         verticalArrangement = Arrangement.spacedBy(6.dp),
     ) {
         cite.blocks.forEach { block ->

composeApp/src/commonMain/kotlin/net/sergeych/toread/ReaderScreen.kt

@@ -70,6 +70,7 @@ import androidx.compose.material3.SnackbarDuration
 import androidx.compose.material3.SnackbarHost
 import androidx.compose.material3.SnackbarHostState
 import androidx.compose.material3.Slider
+import androidx.compose.material3.Switch
 import androidx.compose.material3.Surface
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
@@ -151,6 +152,7 @@ internal fun BookView(
     var readerExtraSettingsVisible by remember(fileId) { mutableStateOf(false) }
     var readerColorPickerTarget by remember(fileId) { mutableStateOf<ReaderColorPickerTarget?>(null) }
     var fullScreenReader by remember { mutableStateOf(false) }
+    var readerPagingOnly by remember { mutableStateOf(false) }
     var tableOfContentsVisible by remember(fileId) { mutableStateOf(false) }
     var tableOfContentsBackStack by remember(fileId) { mutableStateOf<List<ReadingPosition>>(emptyList()) }
     var tableOfContentsBackPosition by remember(fileId) { mutableStateOf<ReadingPosition?>(null) }
@@ -233,6 +235,14 @@ internal fun BookView(
         }
     }
 
+    fun updateReaderPagingOnly(pagingOnly: Boolean) {
+        if (pagingOnly == readerPagingOnly) return
+        readerPagingOnly = pagingOnly
+        scope.launch {
+            saveReaderPagingOnly(pagingOnly)
+        }
+    }
+
     fun currentReadingPosition(backStack: List<ReadingPosition> = tableOfContentsBackStack): ReadingPosition =
         ReadingPosition(
             listState.firstVisibleItemIndex,
@@ -302,6 +312,7 @@ internal fun BookView(
     LaunchedEffect(Unit) {
         readerFontSettings = loadReaderFontSettings()
         fullScreenReader = loadReaderFullScreen()
+        readerPagingOnly = loadReaderPagingOnly()
     }
 
     DisposableEffect(fileId) {
@@ -436,11 +447,17 @@ internal fun BookView(
                     },
                     showReadAloudAction = showReadAloudAction,
                     onReadAloud = {
-                        val position = currentReadingPosition()
-                        val startIndex = contentPlan.resumeSentenceIndex(position)
+                        if (readAloudPanelVisible) {
+                            ReadAloudPlatform.stop()
+                            readAloudPanelVisible = false
+                        } else {
+                            if (!readAloudState.active) {
+                                val startIndex = contentPlan.resumeSentenceIndex(currentReadingPosition())
                                 ReadAloudPlatform.prepare(fileId, book.title, contentPlan.sentences, startIndex)
+                            }
                             readAloudPanelVisible = true
                             ReadAloudPlatform.play()
+                        }
                     },
                     onDelete = {
                         onDeleteRequested(
@@ -489,6 +506,7 @@ internal fun BookView(
                     readerFontSettings = readerFontSettings,
                     readerBackgroundColor = readerBackgroundColor,
                     readerTextColor = readerTextColor,
+                    pagingOnly = readerPagingOnly,
                     onReaderFontZoom = { steps ->
                         updateReaderFontSettings { settings -> settings.adjustFontSize(steps) }
                     },
@@ -550,15 +568,18 @@ internal fun BookView(
                         onClose = { readerSettingsPanelVisible = false },
                     )
                 }
-                if (readAloudPanelVisible && readAloudState.active) {
+                if (readAloudPanelVisible) {
                     ReadAloudPanel(
                         playing = readAloudState.playing,
                         buffering = readAloudState.buffering,
                         onPlayStop = {
                             if (readAloudState.playing) {
                                 ReadAloudPlatform.stop()
-                                readAloudPanelVisible = false
                             } else {
+                                if (!readAloudState.active) {
+                                    val startIndex = contentPlan.resumeSentenceIndex(currentReadingPosition())
+                                    ReadAloudPlatform.prepare(fileId, book.title, contentPlan.sentences, startIndex)
+                                }
                                 ReadAloudPlatform.play()
                             }
                         },
@@ -596,6 +617,8 @@ internal fun BookView(
             onRevertColorScheme = {
                 updateReaderFontSettings { settings -> settings.resetThemeColorScheme(useDarkReaderTheme) }
             },
+            pagingOnly = readerPagingOnly,
+            onPagingOnlyChange = { pagingOnly -> updateReaderPagingOnly(pagingOnly) },
             onDismiss = { readerExtraSettingsVisible = false },
         )
     }
@@ -1384,6 +1407,8 @@ private fun ColorSwatchIcon(color: Color) {
 @Composable
 private fun ReaderExtraSettingsDialog(
     onRevertColorScheme: () -> Unit,
+    pagingOnly: Boolean,
+    onPagingOnlyChange: (Boolean) -> Unit,
     onDismiss: () -> Unit,
 ) {
     AlertDialog(
@@ -1417,6 +1442,30 @@ private fun ReaderExtraSettingsDialog(
                     }
                     HorizontalDivider()
                 }
+                Row(
+                    modifier = Modifier
+                        .fillMaxWidth()
+                        .clickable { onPagingOnlyChange(!pagingOnly) }
+                        .padding(horizontal = 4.dp, vertical = 8.dp),
+                    verticalAlignment = Alignment.CenterVertically,
+                ) {
+                    Column(Modifier.weight(1f)) {
+                        Text(
+                            text = strings.readerNavigation,
+                            style = MaterialTheme.typography.bodyLarge,
+                        )
+                        Text(
+                            text = strings.readerPagingOnly,
+                            style = MaterialTheme.typography.bodyMedium,
+                            color = MaterialTheme.colorScheme.outline,
+                        )
+                    }
+                    Switch(
+                        checked = pagingOnly,
+                        onCheckedChange = { onPagingOnlyChange(it) },
+                    )
+                }
+                HorizontalDivider()
             }
         },
         confirmButton = {
@@ -1542,7 +1591,6 @@ private fun readerExtraSettingOptions(): List<String> =
         strings.readerColors,
         strings.readerTypography,
         strings.readerLayout,
-        strings.readerNavigation,
         strings.readerProgress,
     )
 

composeApp/src/commonTest/kotlin/net/sergeych/toread/ReadAloudBlocksTest.kt

@@ -0,0 +1,58 @@
+package net.sergeych.toread
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class ReadAloudBlocksTest {
+    private fun sentence(index: Int, item: Int, text: String, before: Long = 0, after: Long = 0) =
+        ReadAloudSentence(index, item, 0, text.length, text, pauseBeforeMillis = before, pauseAfterMillis = after)
+
+    @Test
+    fun paragraphsKeepContextAndRangesUseSpokenText() {
+        val queue = listOf(
+            sentence(0, 1, "Первое.").copy(spokenText = "Пе́рвое."),
+            sentence(1, 1, "Второе."), sentence(2, 2, "Другой абзац."),
+        )
+        val blocks = readAloudBlocks(queue, 0, 4_000).toList()
+        assertEquals(listOf("Пе́рвое. Второе.", "Другой абзац."), blocks.map { it.text })
+        assertEquals(0, blocks[0].positionAt(0))
+        assertEquals(1, blocks[0].positionAt(9))
+        assertEquals(listOf("Второе.", "Другой абзац."), readAloudBlocks(queue, 1, 4_000).map { it.text }.toList())
+    }
+
+    @Test
+    fun longParagraphBreaksBetweenSentencesAndCountsCharacters() {
+        val queue = (0..9).map { sentence(it, 1, "я".repeat(998) + ".") }
+        val blocks = readAloudBlocks(queue, 0, 4_000).toList()
+        assertEquals(listOf(3_999, 3_999, 1_999), blocks.map { it.text.length })
+        assertEquals((0..9).toList(), blocks.flatMap { it.ranges }.map { it.position })
+    }
+
+    @Test
+    fun oversizedSentenceSplitsAtWordsAndNeverCutsSurrogatePairs() {
+        val words = List(20) { "Привет😀" }
+        val blocks = readAloudBlocks(listOf(sentence(0, 0, words.joinToString(" "))), 0, 30).toList()
+        assertEquals(words.joinToString(" "), blocks.joinToString(" ") { it.text })
+        assertTrue(blocks.all { it.text.length <= 30 })
+        val cyrillic = "я".repeat(9_001) + "."
+        val cyrillicBlocks = readAloudBlocks(listOf(sentence(0, 0, cyrillic)), 0, 4_000).toList()
+        assertEquals(cyrillic, cyrillicBlocks.joinToString("") { it.text })
+        assertEquals(listOf(4_000, 4_000, 1_002), cyrillicBlocks.map { it.text.length })
+        val giantWord = "😀".repeat(4_001)
+        val split = readAloudBlocks(listOf(sentence(0, 0, giantWord)), 0, 3_999).toList()
+        assertEquals(giantWord, split.joinToString("") { it.text })
+        assertTrue(split.all { it.text.length <= 3_999 && !it.text.last().isHighSurrogate() })
+    }
+
+    @Test
+    fun pausesAndStartingPositionArePreserved() {
+        val queue = listOf(sentence(0, 0, "Skip."), sentence(1, 0, "Heading.", 1000, 600),
+            sentence(2, 1, "Wait.", after = 350), sentence(3, 1, "Go."))
+        val blocks = readAloudBlocks(queue, 1, 4_000).toList()
+        assertEquals(listOf("Heading.", "Wait.", "Go."), blocks.map { it.text })
+        assertEquals(listOf(1000L, 0L, 0L), blocks.map { it.pauseBeforeMillis })
+        assertEquals(listOf(600L, 350L, 0L), blocks.map { it.pauseAfterMillis })
+        assertEquals(listOf(1, 2, 3), blocks.map { it.ranges.first().position })
+    }
+}

composeApp/src/jvmMain/kotlin/net/sergeych/toread/BookPlatform.jvm.kt

@@ -461,6 +461,18 @@ actual suspend fun saveReaderFullScreen(fullScreen: Boolean) = withContext(Dispa
     }
 }
 
+actual suspend fun loadReaderPagingOnly(): Boolean = withContext(Dispatchers.IO) {
+    openLibraryDatabase().useLibrary { db ->
+        db.getAppFlag(ReaderPagingOnlyFlag)?.toBooleanStrictOrNull() ?: false
+    }
+}
+
+actual suspend fun saveReaderPagingOnly(enabled: Boolean) = withContext(Dispatchers.IO) {
+    openLibraryDatabase().useLibrary { db ->
+        db.setAppFlag(ReaderPagingOnlyFlag, enabled.toString())
+    }
+}
+
 actual suspend fun loadScanDownloadsAutomatically(): Boolean = withContext(Dispatchers.IO) {
     openLibraryDatabase().useLibrary { db ->
         db.getAppFlag(ScanDownloadsAutomaticallyFlag)?.toBooleanStrictOrNull() ?: true
@@ -751,6 +763,7 @@ private const val ActiveReadingFileIdFlag = "active_reading_file_id"
 private const val ThemeModeFlag = "theme_mode"
 private const val ReaderFontSettingsFlag = "reader_font_settings"
 private const val ReaderFullScreenFlag = "reader_full_screen"
+private const val ReaderPagingOnlyFlag = "reader_paging_only"
 private const val ScanDownloadsAutomaticallyFlag = "scan_downloads_automatically"
 private const val LibraryFilterFlag = "library_filter"
 private const val AppLocaleTagFlag = "app_locale_tag"

composeApp/src/webMain/kotlin/net/sergeych/toread/BookPlatform.web.kt

@@ -90,6 +90,13 @@ actual suspend fun saveReaderFullScreen(fullScreen: Boolean) {
     window.localStorage.setItem(ReaderFullScreenStorageKey, fullScreen.toString())
 }
 
+actual suspend fun loadReaderPagingOnly(): Boolean =
+    window.localStorage.getItem(ReaderPagingOnlyStorageKey)?.toBooleanStrictOrNull() ?: false
+
+actual suspend fun saveReaderPagingOnly(enabled: Boolean) {
+    window.localStorage.setItem(ReaderPagingOnlyStorageKey, enabled.toString())
+}
+
 actual suspend fun loadScanDownloadsAutomatically(): Boolean = true
 
 actual suspend fun saveScanDownloadsAutomatically(enabled: Boolean) = Unit
@@ -152,6 +159,7 @@ private const val AppLocaleStorageKey = "toread.appLocaleTag"
 private const val LibraryFilterStorageKey = "toread.libraryFilter"
 private const val ReaderFontSettingsStorageKey = "toread.readerFontSettings"
 private const val ReaderFullScreenStorageKey = "toread.readerFullScreen"
+private const val ReaderPagingOnlyStorageKey = "toread.readerPagingOnly"
 
 actual fun formatLibraryLastReadTime(millis: Long): String {
     val totalMinutes = millis / 60_000L