Webtoon reader scroll with pan

app/src/main/java/org/koitharu/kotatsu/ui/reader/wetoon/WebtoonAdapter.kt

@@ -1,16 +1,29 @@
 package org.koitharu.kotatsu.ui.reader.wetoon
 
+import android.view.Gravity
 import android.view.ViewGroup
 import org.koitharu.kotatsu.core.model.MangaPage
 import org.koitharu.kotatsu.ui.common.list.BaseRecyclerAdapter
+import org.koitharu.kotatsu.ui.common.list.BaseViewHolder
 import org.koitharu.kotatsu.ui.reader.PageLoader
 
-class WebtoonAdapter(private val loader: PageLoader) : BaseRecyclerAdapter<MangaPage, Unit>() {
+class WebtoonAdapter(private val loader: PageLoader) : BaseRecyclerAdapter<MangaPage, Int>() {
+
+	private var lastBound = -1
 
 	override fun onCreateViewHolder(parent: ViewGroup) =
 		WebtoonHolder(parent, loader)
 
 	override fun onGetItemId(item: MangaPage) = item.id
 
-	override fun getExtra(item: MangaPage, position: Int) = Unit
+	override fun onBindViewHolder(holder: BaseViewHolder<MangaPage, Int>, position: Int) {
+		super.onBindViewHolder(holder, position)
+		lastBound = position
+	}
+
+	override fun getExtra(item: MangaPage, position: Int) = if (position >= lastBound) {
+		Gravity.TOP
+	} else {
+		Gravity.BOTTOM
+	}
 }

app/src/main/java/org/koitharu/kotatsu/ui/reader/wetoon/WebtoonFrameLayout.kt

@@ -0,0 +1,41 @@
+package org.koitharu.kotatsu.ui.reader.wetoon
+
+import android.content.Context
+import android.graphics.RectF
+import android.util.AttributeSet
+import android.widget.FrameLayout
+import com.davemorrissey.labs.subscaleview.SubsamplingScaleImageView
+import kotlinx.android.synthetic.main.item_page_webtoon.view.*
+import org.koitharu.kotatsu.R
+
+class WebtoonFrameLayout @JvmOverloads constructor(
+	context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
+) : FrameLayout(context, attrs, defStyleAttr) {
+
+	private val pan = RectF()
+
+	private val target by lazy {
+		findViewById<SubsamplingScaleImageView>(R.id.ssiv)
+	}
+
+	fun dispatchVerticalScroll(dy: Int): Int {
+		target.getPanRemaining(pan)
+		val c = target.center ?: return 0
+		val s = target.scale
+		return when {
+			dy > 0 -> {
+				val delta = minOf(pan.bottom.toInt(), dy)
+				c.offset(0f, delta.toFloat() / s)
+				target.setScaleAndCenter(s, c)
+				delta
+			}
+			dy < 0 -> {
+				val delta = minOf(pan.top.toInt(), -dy)
+				c.offset(0f, -delta.toFloat() / s)
+				target.setScaleAndCenter(s, c)
+				-delta
+			}
+			else -> 0
+		}
+	}
+}

app/src/main/java/org/koitharu/kotatsu/ui/reader/wetoon/WebtoonHolder.kt

@@ -1,6 +1,7 @@
 package org.koitharu.kotatsu.ui.reader.wetoon
 
 import android.graphics.PointF
+import android.view.Gravity
 import android.view.ViewGroup
 import androidx.core.net.toUri
 import androidx.core.view.isVisible
@@ -16,10 +17,11 @@ import org.koitharu.kotatsu.utils.ext.getDisplayMessage
 
 
 class WebtoonHolder(parent: ViewGroup, private val loader: PageLoader) :
-	BaseViewHolder<MangaPage, Unit>(parent, R.layout.item_page_webtoon),
+	BaseViewHolder<MangaPage, Int>(parent, R.layout.item_page_webtoon),
 	SubsamplingScaleImageView.OnImageEventListener, CoroutineScope by loader {
 
 	private var job: Job? = null
+	private var yFactor = 0f
 
 	init {
 		ssiv.setOnImageEventListener(this)
@@ -28,7 +30,12 @@ class WebtoonHolder(parent: ViewGroup, private val loader: PageLoader) :
 		}
 	}
 
-	override fun onBind(data: MangaPage, extra: Unit) {
+	override fun onBind(data: MangaPage, extra: Int) {
+		yFactor = when(extra) {
+			Gravity.TOP -> 0f
+			Gravity.BOTTOM -> 1f
+			else -> 0.5f
+		}
 		doLoad(data, force = false)
 	}
 
@@ -56,7 +63,7 @@ class WebtoonHolder(parent: ViewGroup, private val loader: PageLoader) :
 		ssiv.minScale = ssiv.width / ssiv.sWidth.toFloat()
 		ssiv.setScaleAndCenter(
 			ssiv.minScale,
-			PointF(ssiv.sWidth / 2f, 0f)
+			PointF(ssiv.sWidth / 2f, ssiv.sHeight * yFactor)
 		)
 	}
 

app/src/main/java/org/koitharu/kotatsu/ui/reader/wetoon/WebtoonImageView.kt

@@ -1,15 +0,0 @@
-package org.koitharu.kotatsu.ui.reader.wetoon
-
-import android.annotation.SuppressLint
-import android.content.Context
-import android.util.AttributeSet
-import android.view.MotionEvent
-import com.davemorrissey.labs.subscaleview.SubsamplingScaleImageView
-
-class WebtoonImageView @JvmOverloads constructor(context: Context, attr: AttributeSet? = null) :
-	SubsamplingScaleImageView(context, attr) {
-
-	@SuppressLint("ClickableViewAccessibility")
-	override fun onTouchEvent(event: MotionEvent) = false
-
-}

app/src/main/java/org/koitharu/kotatsu/ui/reader/wetoon/WebtoonRecyclerView.kt

@@ -3,13 +3,46 @@ package org.koitharu.kotatsu.ui.reader.wetoon
 import android.content.Context
 import android.util.AttributeSet
 import android.view.View
+import androidx.core.view.children
 import androidx.recyclerview.widget.RecyclerView
 
 class WebtoonRecyclerView @JvmOverloads constructor(
 	context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
 ) : RecyclerView(context, attrs, defStyleAttr) {
 
-	override fun onNestedPreScroll(target: View?, dx: Int, dy: Int, consumed: IntArray?) {
+	override fun dispatchNestedPreScroll(
-		super.onNestedPreScroll(target, dx, dy, consumed)
+		dx: Int,
+		dy: Int,
+		consumed: IntArray?,
+		offsetInWindow: IntArray?,
+		type: Int
+	): Boolean {
+		val consumedY = consumeVerticalScroll(dy)
+		val superRes = super.dispatchNestedPreScroll(dx, dy, consumed, offsetInWindow, type)
+		consumed?.set(1, consumed[1] + consumedY)
+		return superRes || consumedY != 0
+	}
+
+	override fun dispatchNestedPreScroll(
+		dx: Int,
+		dy: Int,
+		consumed: IntArray?,
+		offsetInWindow: IntArray?
+	): Boolean {
+		val consumedY = consumeVerticalScroll(dy)
+		val superRes = super.dispatchNestedPreScroll(dx, dy, consumed, offsetInWindow)
+		consumed?.set(1, consumed[1] + consumedY)
+		return superRes || consumedY != 0
+	}
+
+	private fun consumeVerticalScroll(dy: Int): Int {
+		val child = when {
+			dy > 0 -> children.firstOrNull { it is WebtoonFrameLayout }
+			dy < 0 -> children.lastOrNull { it is WebtoonFrameLayout }
+			else -> null
+		} ?: return 0
+		var scrollY = dy
+		scrollY -= (child as WebtoonFrameLayout) .dispatchVerticalScroll(scrollY)
+		return dy - scrollY
 	}
 }

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

@@ -1,14 +1,16 @@
 <?xml version="1.0" encoding="utf-8"?>
-<FrameLayout
+<org.koitharu.kotatsu.ui.reader.wetoon.WebtoonFrameLayout
 	xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:app="http://schemas.android.com/apk/res-auto"
 	xmlns:tools="http://schemas.android.com/tools"
 	android:layout_width="match_parent"
 	android:layout_height="match_parent">
 
-	<org.koitharu.kotatsu.ui.reader.wetoon.WebtoonImageView
+	<com.davemorrissey.labs.subscaleview.SubsamplingScaleImageView
 		android:id="@+id/ssiv"
 		android:layout_width="match_parent"
-		android:layout_height="match_parent" />
+		android:layout_height="match_parent"
+		app:panEnabled="false" />
 
 	<ProgressBar
 		android:id="@+id/progressBar"
@@ -48,4 +50,4 @@
 
 	</LinearLayout>
 
-</FrameLayout>
+</org.koitharu.kotatsu.ui.reader.wetoon.WebtoonFrameLayout>