Improve live text reader repagination

app/src/main/java/eu/kanade/presentation/reader/settings/GeneralSettingsPage.kt

@@ -53,7 +53,7 @@ internal fun ColumnScope.GeneralPage(viewModel: ReaderSettingsViewModel) {
                 selected = readerTheme == value,
                 onClick = {
                     viewModel.preferences.readerTheme.set(value)
-                    viewModel.requestTextSettingsReload()
+                    viewModel.requestTextAppearanceReload()
                 },
                 label = { Text(stringResource(labelRes)) },
             )

app/src/main/java/eu/kanade/tachiyomi/ui/reader/ReaderViewModel.kt

@@ -57,6 +57,7 @@ import eu.kanade.tachiyomi.util.storage.DiskUtil
 import eu.kanade.tachiyomi.util.storage.cacheImageDir
 import kotlinx.coroutines.CancellationException
 import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.channels.Channel
 import kotlinx.coroutines.flow.MutableStateFlow
@@ -186,6 +187,12 @@ class ReaderViewModel(
      */
     private var loader: ChapterLoader? = null
 
+    /**
+     * Only the newest text repagination request is allowed to finish. Slider
+     * changes can arrive faster than a large TXT/EPUB chapter can be rebuilt.
+     */
+    private var textRepaginationJob: Job? = null
+
     /**
      * The time the chapter was started reading
      */
@@ -841,17 +848,26 @@ class ReaderViewModel(
         if (chapter.pageLoader?.usesTextReaderStyle != true) return
         if (chapter.pages?.any { it is TextReaderPage } != true) return
         val chapterLoader = loader ?: return
-        val requestedPage = (state.value.currentPage - 1).coerceAtLeast(0)
-        val oldLastIndex = (chapter.pages?.lastIndex ?: 0).coerceAtLeast(0)
-        val readingProgress = if (oldLastIndex == 0) 0f else requestedPage.toFloat() / oldLastIndex
 
-        viewModelScope.launchIO {
+        val oldPageCount = chapter.pages?.size?.coerceAtLeast(1) ?: 1
+        val requestedPage = chapter.requestedPage.coerceIn(0, oldPageCount - 1)
+        // Anchor at the middle of the visible page so position remains stable
+        // when font size/spacing changes the total page count.
+        val readingProgress = ((requestedPage + 0.5f) / oldPageCount)
+            .coerceIn(0f, 0.999999f)
+
+        textRepaginationJob?.cancel()
+        textRepaginationJob = viewModelScope.launchIO {
             try {
                 val oldLoader = chapterLoader.reloadTextChapter(chapter, readingProgress) ?: return@launchIO
-                eventChannel.send(Event.ReloadTextViewerChapters)
+
-                // Give old visible holders time to detach before closing resources such as EpubReader.
+                // Resource cleanup must survive cancellation by the next slider value.
-                delay(2000)
+                viewModelScope.launchNonCancellable {
+                    delay(750)
                     oldLoader.recycle()
+                }
+
+                eventChannel.trySend(Event.ReloadTextViewerChapters)
             } catch (e: Throwable) {
                 if (e is CancellationException) throw e
                 logcat(LogPriority.ERROR, e) { "Failed to repaginate text reader style" }

app/src/main/java/eu/kanade/tachiyomi/ui/reader/loader/ChapterLoader.kt

@@ -22,7 +22,8 @@ import tachiyomi.domain.source.model.StubSource
 import tachiyomi.i18n.MR
 import tachiyomi.source.local.LocalSource
 import tachiyomi.source.local.io.Format
-import kotlin.math.roundToInt
+import kotlinx.coroutines.currentCoroutineContext
+import kotlinx.coroutines.ensureActive
 
 /**
  * Loader used to retrieve the [PageLoader] for a given chapter.
@@ -90,10 +91,14 @@ class ChapterLoader(
                     throw Exception(context.stringResource(MR.strings.page_list_empty_error))
                 }
 
+                // If a newer slider value cancelled this rebuild while getPages()
+                // was working, do not publish stale pages into the active chapter.
+                currentCoroutineContext().ensureActive()
+
                 val oldLoader = chapter.pageLoader
                 chapter.pageLoader = newLoader
-                chapter.requestedPage = (readingProgress * pages.lastIndex)
+                chapter.requestedPage = (readingProgress.coerceIn(0f, 0.999999f) * pages.size)
-                    .roundToInt()
+                    .toInt()
                     .coerceIn(0, pages.lastIndex)
                 chapter.state = ReaderChapter.State.Loaded(pages)
                 oldLoader

app/src/main/java/eu/kanade/tachiyomi/ui/reader/loader/TextPageRenderer.kt

@@ -16,13 +16,10 @@ import java.io.ByteArrayInputStream
 import java.io.ByteArrayOutputStream
 import java.io.InputStream
 import java.io.Reader
+import kotlin.math.roundToInt
 
 internal object TextPageRenderer {
-    private const val PAGE_WIDTH = 1440
+    private const val MARGIN_DP = 32f
-    private const val PAGE_HEIGHT = 2160
-    private const val MARGIN = 96
-    private const val CONTENT_WIDTH = PAGE_WIDTH - (MARGIN * 2)
-    private const val CONTENT_HEIGHT = PAGE_HEIGHT - (MARGIN * 2)
     private const val STREAM_BUFFER_CHARS = 64 * 1024
     private const val STREAM_READ_CHARS = 8 * 1024
 
@@ -101,7 +98,8 @@ internal object TextPageRenderer {
     private fun calculatePageSlices(text: String, style: TextReaderStyle): List<PageSlice> {
         if (text.isEmpty()) return emptyList()
 
-        val layout = createLayout(text, style)
+        val metrics = resolveLayoutMetrics(style)
+        val layout = createLayout(text, style, metrics.contentWidth)
         if (layout.lineCount == 0) return listOf(PageSlice(0, text.length))
 
         val pages = mutableListOf<PageSlice>()
@@ -111,7 +109,7 @@ internal object TextPageRenderer {
             var endLine = startLine
             while (
                 endLine + 1 < layout.lineCount &&
-                layout.getLineBottom(endLine + 1) - startTop <= CONTENT_HEIGHT
+                layout.getLineBottom(endLine + 1) - startTop <= metrics.contentHeight
             ) {
                 endLine++
             }
@@ -125,13 +123,14 @@ internal object TextPageRenderer {
     }
 
     fun render(text: String, style: TextReaderStyle): InputStream {
-        val bitmap = Bitmap.createBitmap(PAGE_WIDTH, PAGE_HEIGHT, Bitmap.Config.ARGB_8888)
+        val metrics = resolveLayoutMetrics(style)
+        val bitmap = Bitmap.createBitmap(metrics.pageWidth, metrics.pageHeight, Bitmap.Config.ARGB_8888)
         val canvas = Canvas(bitmap)
         val (backgroundColor, _) = resolveColors(style)
         canvas.drawColor(backgroundColor)
         canvas.save()
-        canvas.translate(MARGIN.toFloat(), MARGIN.toFloat())
+        canvas.translate(metrics.horizontalMargin.toFloat(), metrics.verticalMargin.toFloat())
-        createLayout(text, style).draw(canvas)
+        createLayout(text, style, metrics.contentWidth).draw(canvas)
         canvas.restore()
 
         val output = ByteArrayOutputStream()
@@ -140,25 +139,46 @@ internal object TextPageRenderer {
         return ByteArrayInputStream(output.toByteArray())
     }
 
-    private fun createLayout(text: String, style: TextReaderStyle): StaticLayout {
+    private fun createLayout(
+        text: String,
+        style: TextReaderStyle,
+        contentWidth: Int,
+    ): StaticLayout {
         val (_, textColor) = resolveColors(style)
         val paint = TextPaint().apply {
             isAntiAlias = true
             color = textColor
-            textSize = style.fontSize * 3f
+            textSize = style.fontSizePx.coerceAtLeast(1f)
             typeface = style.fontFamily.androidFamilyName
                 ?.let { Typeface.create(it, Typeface.NORMAL) }
                 ?: Typeface.DEFAULT
         }
-        val styledText = addParagraphSpacing(text, style.paragraphSpacing * 3)
+        val styledText = addParagraphSpacing(text, style.paragraphSpacingPx)
         return StaticLayout.Builder
-            .obtain(styledText, 0, styledText.length, paint, CONTENT_WIDTH)
+            .obtain(styledText, 0, styledText.length, paint, contentWidth)
             .setAlignment(Layout.Alignment.ALIGN_NORMAL)
             .setIncludePad(true)
             .setLineSpacing(0f, style.lineSpacingPercent / 100f)
             .build()
     }
 
+    private fun resolveLayoutMetrics(style: TextReaderStyle): LayoutMetrics {
+        val pageWidth = style.pageWidthPx.coerceAtLeast(1)
+        val pageHeight = style.pageHeightPx.coerceAtLeast(1)
+        val requestedMargin = (MARGIN_DP * style.density).roundToInt().coerceAtLeast(1)
+        val horizontalMargin = requestedMargin.coerceAtMost(((pageWidth - 1) / 2).coerceAtLeast(0))
+        val verticalMargin = requestedMargin.coerceAtMost(((pageHeight - 1) / 2).coerceAtLeast(0))
+
+        return LayoutMetrics(
+            pageWidth = pageWidth,
+            pageHeight = pageHeight,
+            horizontalMargin = horizontalMargin,
+            verticalMargin = verticalMargin,
+            contentWidth = (pageWidth - horizontalMargin * 2).coerceAtLeast(1),
+            contentHeight = (pageHeight - verticalMargin * 2).coerceAtLeast(1),
+        )
+    }
+
     private fun resolveColors(style: TextReaderStyle): Pair<Int, Int> {
         val useDark = when (style.readerTheme) {
             0 -> false
@@ -205,6 +225,15 @@ internal object TextPageRenderer {
         }
     }
 
+    private data class LayoutMetrics(
+        val pageWidth: Int,
+        val pageHeight: Int,
+        val horizontalMargin: Int,
+        val verticalMargin: Int,
+        val contentWidth: Int,
+        val contentHeight: Int,
+    )
+
     private data class PageSlice(
         val start: Int,
         val endExclusive: Int,

app/src/main/java/eu/kanade/tachiyomi/ui/reader/loader/TextReaderPage.kt

@@ -5,9 +5,8 @@ import eu.kanade.tachiyomi.ui.reader.model.ReaderPage
 import eu.kanade.tachiyomi.ui.reader.setting.TextReaderStyle
 
 /**
- * A rendered text page whose style can be changed without rebuilding the chapter.
+ * A rendered text page whose visual style can be refreshed cheaply while layout-affecting
- * Page boundaries remain stable during the live preview; a full repagination is done
+ * changes trigger a debounced chapter repagination to rebuild page boundaries.
- * once when the settings dialog is dismissed.
  */
 internal class TextReaderPage(
     index: Int,

app/src/main/java/eu/kanade/tachiyomi/ui/reader/setting/ReaderPreferences.kt

@@ -3,6 +3,7 @@ package eu.kanade.tachiyomi.ui.reader.setting
 import android.content.Context
 import android.content.res.Configuration
 import android.os.Build
+import android.util.TypedValue
 import androidx.compose.ui.graphics.BlendMode
 import dev.icerock.moko.resources.StringResource
 import dev.zacsweers.metro.AppScope
@@ -137,7 +138,20 @@ class ReaderPreferences(
         }
     }
 
-    fun textReaderStyle(context: Context) = TextReaderStyle(
+    fun textReaderStyle(context: Context): TextReaderStyle {
+        val displayMetrics = context.resources.displayMetrics
+        val rawWidth = displayMetrics.widthPixels.coerceAtLeast(1)
+        val rawHeight = displayMetrics.heightPixels.coerceAtLeast(1)
+
+        // Keep the same physical page proportions as the device while capping the
+        // raster size so high-resolution phones do not create oversized bitmaps.
+        val renderScale = minOf(
+            1f,
+            TEXT_READER_MAX_RENDER_WIDTH / rawWidth.toFloat(),
+            TEXT_READER_MAX_RENDER_HEIGHT / rawHeight.toFloat(),
+        )
+
+        return TextReaderStyle(
             fontSize = textFontSize.get(),
             lineSpacingPercent = textLineSpacing.get(),
             paragraphSpacing = textParagraphSpacing.get(),
@@ -145,7 +159,23 @@ class ReaderPreferences(
             readerTheme = readerTheme.get(),
             automaticDark = (context.resources.configuration.uiMode and Configuration.UI_MODE_NIGHT_MASK) ==
                 Configuration.UI_MODE_NIGHT_YES,
+            pageWidthPx = (rawWidth * renderScale).roundToInt().coerceAtLeast(1),
+            pageHeightPx = (rawHeight * renderScale).roundToInt().coerceAtLeast(1),
+            density = displayMetrics.density * renderScale,
+            fontSizePx = TypedValue.applyDimension(
+                TypedValue.COMPLEX_UNIT_SP,
+                textFontSize.get().toFloat(),
+                displayMetrics,
+            ) * renderScale,
+            paragraphSpacingPx = (
+                TypedValue.applyDimension(
+                    TypedValue.COMPLEX_UNIT_DIP,
+                    textParagraphSpacing.get().toFloat(),
+                    displayMetrics,
+                ) * renderScale
+                ).roundToInt(),
         )
+    }
 
     // endregion
 
@@ -336,6 +366,9 @@ class ReaderPreferences(
         const val WEBTOON_PADDING_MIN = 0
         const val WEBTOON_PADDING_MAX = 25
 
+        private const val TEXT_READER_MAX_RENDER_WIDTH = 1440
+        private const val TEXT_READER_MAX_RENDER_HEIGHT = 2400
+
         const val MILLI_CONVERSION = 100
 
         val TapZones = listOf(
@@ -399,4 +432,9 @@ data class TextReaderStyle(
     val fontFamily: ReaderPreferences.TextFontFamily,
     val readerTheme: Int,
     val automaticDark: Boolean,
+    val pageWidthPx: Int,
+    val pageHeightPx: Int,
+    val density: Float,
+    val fontSizePx: Float,
+    val paragraphSpacingPx: Int,
 )

app/src/main/java/eu/kanade/tachiyomi/ui/reader/setting/ReaderSettingsViewModel.kt

@@ -32,20 +32,49 @@ class ReaderSettingsViewModel(
         .stateIn(viewModelScope, SharingStarted.Lazily, null)
 
     private var textSettingsReloadJob: Job? = null
+    private var textAppearanceReloadJob: Job? = null
     private var textSettingsDirty = false
 
+    /**
+     * Layout-affecting text settings are previewed quickly, then the chapter is
+     * repaginated after a short debounce. This keeps the slider responsive while
+     * ensuring the number of characters/lines on a page follows the new style.
+     */
     fun requestTextSettingsReload() {
         textSettingsDirty = true
         textSettingsReloadJob?.cancel()
         textSettingsReloadJob = viewModelScope.launch {
-            delay(200)
+            delay(250)
             onTextSettingsPreview()
+            textSettingsDirty = false
+            onTextSettingsCommit()
             textSettingsReloadJob = null
         }
     }
 
+    /**
+     * Theme-only changes do not affect page boundaries, so avoid an unnecessary
+     * full repagination.
+     */
+    fun requestTextAppearanceReload() {
+        textAppearanceReloadJob?.cancel()
+        textAppearanceReloadJob = viewModelScope.launch {
+            delay(50)
+            onTextSettingsPreview()
+            textAppearanceReloadJob = null
+        }
+    }
+
     fun flushTextSettingsReload() {
-        if (!textSettingsDirty) return
+        val hadPendingAppearanceReload = textAppearanceReloadJob != null
+        textAppearanceReloadJob?.cancel()
+        textAppearanceReloadJob = null
+        if (!textSettingsDirty) {
+            if (hadPendingAppearanceReload) {
+                onTextSettingsPreview()
+            }
+            return
+        }
         textSettingsReloadJob?.cancel()
         textSettingsReloadJob = null
         onTextSettingsPreview()