Downsample offscreen pages option

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

@@ -36,6 +36,9 @@ class ReaderSettings(
 	val colorFilter: ReaderColorFilter?
 		get() = colorFilterFlow.value?.takeUnless { it.isEmpty }
 
+	val isReaderOptimizationEnabled: Boolean
+		get() = settings.isReaderOptimizationEnabled
+
 	val bitmapConfig: Bitmap.Config
 		get() = if (settings.is32BitColorsEnabled) {
 			Bitmap.Config.ARGB_8888
@@ -104,7 +107,8 @@ class ReaderSettings(
 				key == AppSettings.KEY_ZOOM_MODE ||
 				key == AppSettings.KEY_PAGES_NUMBERS ||
 				key == AppSettings.KEY_READER_BACKGROUND ||
-				key == AppSettings.KEY_32BIT_COLOR
+				key == AppSettings.KEY_32BIT_COLOR ||
+				key == AppSettings.KEY_READER_OPTIMIZE
 			) {
 				notifyChanged()
 			}

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

@@ -7,6 +7,7 @@ import androidx.viewbinding.ViewBinding
 import org.koitharu.kotatsu.core.exceptions.resolve.ExceptionResolver
 import org.koitharu.kotatsu.core.os.NetworkState
 import org.koitharu.kotatsu.core.ui.list.lifecycle.LifecycleAwareViewHolder
+import org.koitharu.kotatsu.core.util.ext.isLowRamDevice
 import org.koitharu.kotatsu.databinding.LayoutPageInfoBinding
 import org.koitharu.kotatsu.reader.domain.PageLoader
 import org.koitharu.kotatsu.reader.ui.config.ReaderSettings
@@ -67,4 +68,10 @@ abstract class BasePageHolder<B : ViewBinding>(
 	open fun onRecycled() {
 		delegate.onRecycle()
 	}
+
+	protected fun getBackgroundDownsampling() = when {
+		!settings.isReaderOptimizationEnabled -> 1
+		context.isLowRamDevice() -> 8
+		else -> 4
+	}
 }

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

@@ -42,7 +42,9 @@ class PageHolderDelegate(
 	private var error: Throwable? = null
 
 	init {
-		callback.onConfigChanged()
+		scope.launch(Dispatchers.Main) { // the same as post() -- wait until child fields init
+			callback.onConfigChanged()
+		}
 	}
 
 	fun isLoading() = job?.isActive == true

app/src/main/kotlin/org/koitharu/kotatsu/reader/ui/pager/standard/PageHolder.kt

@@ -45,12 +45,22 @@ open class PageHolder(
 		binding.textViewNumber.isVisible = settings.isPagesNumbersEnabled
 	}
 
+	override fun onResume() {
+		super.onResume()
+		binding.ssiv.downsampling = 1
+	}
+
+	override fun onPause() {
+		super.onPause()
+		binding.ssiv.downsampling = getBackgroundDownsampling()
+	}
+
 	override fun onConfigChanged() {
 		super.onConfigChanged()
-		@Suppress("SENSELESS_COMPARISON")
-		if (settings.applyBitmapConfig(binding.ssiv) && delegate != null) {
+		if (settings.applyBitmapConfig(binding.ssiv)) {
 			delegate.reload()
 		}
+		binding.ssiv.downsampling = if (isResumed()) 1 else getBackgroundDownsampling()
 	}
 
 	@SuppressLint("SetTextI18n")

app/src/main/kotlin/org/koitharu/kotatsu/reader/ui/pager/webtoon/WebtoonHolder.kt

@@ -40,10 +40,20 @@ class WebtoonHolder(
 
 	override fun onConfigChanged() {
 		super.onConfigChanged()
-		@Suppress("SENSELESS_COMPARISON")
-		if (settings.applyBitmapConfig(binding.ssiv) && delegate != null) {
+		if (settings.applyBitmapConfig(binding.ssiv)) {
 			delegate.reload()
 		}
+		binding.ssiv.downsampling = if (isResumed()) 1 else getBackgroundDownsampling()
+	}
+
+	override fun onResume() {
+		super.onResume()
+		binding.ssiv.downsampling = 1
+	}
+
+	override fun onPause() {
+		super.onPause()
+		binding.ssiv.downsampling = getBackgroundDownsampling()
 	}
 
 	override fun onBind(data: ReaderPage) {

app/src/main/kotlin/org/koitharu/kotatsu/reader/ui/pager/webtoon/WebtoonReaderFragment.kt

@@ -11,6 +11,7 @@ import kotlinx.coroutines.coroutineScope
 import kotlinx.coroutines.yield
 import org.koitharu.kotatsu.R
 import org.koitharu.kotatsu.core.os.NetworkState
+import org.koitharu.kotatsu.core.ui.list.lifecycle.RecyclerViewLifecycleDispatcher
 import org.koitharu.kotatsu.core.util.ext.findCenterViewPosition
 import org.koitharu.kotatsu.core.util.ext.firstVisibleItemPosition
 import org.koitharu.kotatsu.core.util.ext.observe
@@ -44,6 +45,7 @@ class WebtoonReaderFragment : BaseReaderFragment<FragmentReaderWebtoonBinding>()
 			setHasFixedSize(true)
 			adapter = readerAdapter
 			addOnPageScrollListener(PageScrollListener())
+			addOnScrollListener(RecyclerViewLifecycleDispatcher())
 		}
 		viewModel.isWebtoonZooEnabled.observe(viewLifecycleOwner) {
 			binding.frame.isZoomEnable = it