feat(reader): Add sensitivity setting for double-page mode

This commit introduces a new setting to control the scroll sensitivity of the double-page reader mode.

- A SeekBar has been added to the reader configuration sheet to adjust the sensitivity.
- The DoublePageSnapHelper now uses this setting to calculate the scroll distance.
- The setting is stored in AppSettings.

app/src/main/kotlin/org/koitharu/kotatsu/core/prefs/AppSettings.kt

@@ -138,6 +138,13 @@ class AppSettings @Inject constructor(@ApplicationContext context: Context) {
 		get() = prefs.getBoolean(KEY_READER_DOUBLE_PAGES, false)
 		set(value) = prefs.edit { putBoolean(KEY_READER_DOUBLE_PAGES, value) }
 
+	val readerDoublePagesSensitivity: Float
+		get() = prefs.getFloat(KEY_READER_DOUBLE_PAGES_SENSITIVITY, 12f) / 10f
+
+	fun setReaderDoublePagesSensitivity(value: Float) {
+		prefs.edit { putFloat(KEY_READER_DOUBLE_PAGES_SENSITIVITY, value) }
+	}
+
 	val readerScreenOrientation: Int
 		get() = prefs.getString(KEY_READER_ORIENTATION, null)?.toIntOrNull()
 			?: ActivityInfo.SCREEN_ORIENTATION_UNSPECIFIED
@@ -669,6 +676,7 @@ class AppSettings @Inject constructor(@ApplicationContext context: Context) {
 		const val KEY_REMOTE_SOURCES = "remote_sources"
 		const val KEY_LOCAL_STORAGE = "local_storage"
 		const val KEY_READER_DOUBLE_PAGES = "reader_double_pages"
+		const val KEY_READER_DOUBLE_PAGES_SENSITIVITY = "reader_double_pages_sensitivity"
 		const val KEY_READER_ZOOM_BUTTONS = "reader_zoom_buttons"
 		const val KEY_READER_CONTROL_LTR = "reader_taps_ltr"
 		const val KEY_READER_NAVIGATION_INVERTED = "reader_navigation_inverted"

app/src/main/kotlin/org/koitharu/kotatsu/reader/ui/config/ReaderConfigSheet.kt

@@ -5,6 +5,7 @@ import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
 import android.widget.CompoundButton
+import android.widget.SeekBar
 import androidx.core.view.WindowInsetsCompat
 import androidx.core.view.isGone
 import androidx.core.view.isVisible
@@ -87,6 +88,10 @@ class ReaderConfigSheet :
 		binding.switchDoubleReader.isChecked = settings.isReaderDoubleOnLandscape
 		binding.switchDoubleReader.isEnabled = mode == ReaderMode.STANDARD || mode == ReaderMode.REVERSED
 
+		binding.textSensitivity.isVisible = settings.isReaderDoubleOnLandscape
+		binding.seekbarSensitivity.isVisible = settings.isReaderDoubleOnLandscape
+		binding.seekbarSensitivity.progress = (settings.readerDoublePagesSensitivity * 100).toInt()
+
 		binding.checkableGroup.addOnButtonCheckedListener(this)
 		binding.buttonSavePage.setOnClickListener(this)
 		binding.buttonScreenRotate.setOnClickListener(this)
@@ -97,6 +102,16 @@ class ReaderConfigSheet :
 		binding.buttonBookmark.setOnClickListener(this)
 		binding.switchDoubleReader.setOnCheckedChangeListener(this)
 
+		binding.seekbarSensitivity.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener {
+			override fun onProgressChanged(seekBar: SeekBar?, progress: Int, fromUser: Boolean) {
+				settings.setReaderDoublePagesSensitivity(progress / 10f)
+			}
+
+			override fun onStartTrackingTouch(seekBar: SeekBar?) {}
+
+			override fun onStopTrackingTouch(seekBar: SeekBar?) {}
+		})
+
 		viewModel.isBookmarkAdded.observe(viewLifecycleOwner) {
 			binding.buttonBookmark.setText(if (it) R.string.bookmark_remove else R.string.bookmark_add)
 			binding.buttonBookmark.setCompoundDrawablesRelativeWithIntrinsicBounds(
@@ -170,6 +185,8 @@ class ReaderConfigSheet :
 
 			R.id.switch_double_reader -> {
 				settings.isReaderDoubleOnLandscape = isChecked
+				viewBinding?.textSensitivity?.isVisible = isChecked
+				viewBinding?.seekbarSensitivity?.isVisible = isChecked
 				findParentCallback(Callback::class.java)?.onDoubleModeChanged(isChecked)
 			}
 		}

app/src/main/kotlin/org/koitharu/kotatsu/reader/ui/pager/doublepage/DoublePageSnapHelper.kt

@@ -11,11 +11,14 @@ import androidx.recyclerview.widget.OrientationHelper
 import androidx.recyclerview.widget.RecyclerView
 import androidx.recyclerview.widget.RecyclerView.SmoothScroller.ScrollVectorProvider
 import androidx.recyclerview.widget.SnapHelper
+import org.koitharu.kotatsu.core.prefs.AppSettings
 import kotlin.math.abs
+import kotlin.math.absoluteValue
 import kotlin.math.max
 import kotlin.math.roundToInt
+import kotlin.math.sign
 
-class DoublePageSnapHelper : SnapHelper() {
+class DoublePageSnapHelper(private val settings: AppSettings) : SnapHelper() {
 
 	private lateinit var recyclerView: RecyclerView
 
@@ -248,28 +251,27 @@ class DoublePageSnapHelper : SnapHelper() {
 			equal to zero.
 		 */
 		fun getPositionsToMove(llm: LinearLayoutManager, scroll: Int, itemSize: Int): Int {
-			var positionsToMove: Int
-			positionsToMove = roundUpToBlockSize(abs((scroll.toDouble()) / itemSize).roundToInt())
-			if (positionsToMove < blockSize) {
-				// Must move at least one block
-				positionsToMove = blockSize
-			} else if (positionsToMove > maxPositionsToMove) {
-				// Clamp number of positions to move, so we don't get wild flinging.
-				positionsToMove = maxPositionsToMove
+			val sensitivity = settings.readerDoublePagesSensitivity
+			var positionsToMove = (scroll.toDouble() / (itemSize * (2.5 - sensitivity))).roundToInt()
+
+			// Apply a maximum threshold
+			val maxPages = (4 * sensitivity).roundToInt().coerceAtLeast(1)
+			if (positionsToMove.absoluteValue > maxPages) {
+				positionsToMove = maxPages * positionsToMove.sign
 			}
-			if (scroll < 0) {
-				positionsToMove *= -1
+
+			// Apply a minimum threshold
+			if (positionsToMove == 0 && scroll.absoluteValue > itemSize * 0.2) {
+				positionsToMove = 1 * scroll.sign
 			}
-			if (isRTL) {
-				positionsToMove *= -1
-			}
-			return if (layoutDirectionHelper.isDirectionToBottom(scroll < 0)) {
-				// Scrolling toward the bottom of data.
-				roundDownToBlockSize(llm.findFirstVisibleItemPosition()) + positionsToMove
+
+			val currentPosition = if (layoutDirectionHelper.isDirectionToBottom(scroll < 0)) {
+				llm.findFirstVisibleItemPosition()
 			} else {
-				roundDownToBlockSize(llm.findLastVisibleItemPosition()) + positionsToMove
+				llm.findLastVisibleItemPosition()
 			}
-			// Scrolling toward the top of the data.
+			val targetPos = currentPosition + positionsToMove * 2
+			return roundDownToBlockSize(targetPos)
 		}
 
 		fun isDirectionToBottom(velocityNegative: Boolean): Boolean {

app/src/main/kotlin/org/koitharu/kotatsu/reader/ui/pager/doublepage/DoubleReaderFragment.kt

@@ -13,6 +13,7 @@ import kotlinx.coroutines.launch
 import kotlinx.coroutines.yield
 import org.koitharu.kotatsu.R
 import org.koitharu.kotatsu.core.os.NetworkState
+import org.koitharu.kotatsu.core.prefs.AppSettings
 import org.koitharu.kotatsu.core.ui.list.lifecycle.RecyclerViewLifecycleDispatcher
 import org.koitharu.kotatsu.core.util.ext.firstVisibleItemPosition
 import org.koitharu.kotatsu.databinding.FragmentReaderDoubleBinding
@@ -33,6 +34,9 @@ open class DoubleReaderFragment : BaseReaderFragment<FragmentReaderDoubleBinding
 	@Inject
 	lateinit var pageLoader: PageLoader
 
+	@Inject
+	lateinit var settings: AppSettings
+
 	private var recyclerLifecycleDispatcher: RecyclerViewLifecycleDispatcher? = null
 
 	override fun onCreateViewBinding(
@@ -51,7 +55,7 @@ open class DoubleReaderFragment : BaseReaderFragment<FragmentReaderDoubleBinding
 				addOnScrollListener(it)
 			}
 			addOnScrollListener(PageScrollListener())
-			DoublePageSnapHelper().attachToRecyclerView(this)
+			DoublePageSnapHelper(settings).attachToRecyclerView(this)
 		}
 	}
 

app/src/main/res/layout/sheet_reader_config.xml

@@ -129,6 +129,24 @@
 				android:textColor="?colorOnSurfaceVariant"
 				app:drawableStartCompat="@drawable/ic_split_horizontal" />
 
+			<TextView
+				android:id="@+id/text_sensitivity"
+				android:layout_width="match_parent"
+				android:layout_height="wrap_content"
+				android:layout_marginHorizontal="@dimen/margin_normal"
+				android:layout_marginTop="@dimen/margin_small"
+				android:text="@string/two_page_scroll_sensitivity"
+				android:textAppearance="@style/TextAppearance.Kotatsu.GridTitle" />
+
+			<SeekBar
+				android:id="@+id/seekbar_sensitivity"
+				android:layout_width="match_parent"
+				android:layout_height="wrap_content"
+				android:layout_marginHorizontal="@dimen/margin_normal"
+				android:layout_marginTop="@dimen/margin_small"
+				android:max="100"
+				tools:progress="50" />
+
 			<org.koitharu.kotatsu.core.ui.widgets.ListItemTextView
 				android:id="@+id/button_screen_rotate"
 				android:layout_width="match_parent"

app/src/main/res/values/strings.xml

@@ -572,6 +572,7 @@
 	<string name="none">None</string>
 	<string name="config_reset_confirm">Reset settings to default values? This action cannot be undone.</string>
 	<string name="use_two_pages_landscape">Use two pages layout on landscape orientation (beta)</string>
+	<string name="two_page_scroll_sensitivity">Two-Page Scroll Sensitivity</string>
 	<string name="default_webtoon_zoom_out">Default webtoon zoom out</string>
 	<string name="fullscreen_mode">Fullscreen mode</string>
 	<string name="reader_fullscreen_summary">Hide system status and navigation bars</string>