Fix preload in reader (#1517)

* Fix preload in reader

* Reduce preload page count for ArchivePageLoader

app/src/main/kotlin/com/hippo/ehviewer/gallery/ArchivePageLoader.kt

@@ -91,13 +91,17 @@ class ArchivePageLoader(
 
     override fun onRequest(index: Int) {
         synchronized(mJobMap) {
-            val current = mJobMap[index]
-            if (current?.isActive != true) {
-                mJobMap[index] = launch {
-                    mWorkerMutex.withLock(index) {
-                        mSemaphore.withPermit {
-                            doRealWork(index)
-                        }
+            enqueue(index)
+        }
+    }
+
+    private fun enqueue(index: Int) {
+        val current = mJobMap[index]
+        if (current?.isActive != true) {
+            mJobMap[index] = launch {
+                mWorkerMutex.withLock(index) {
+                    mSemaphore.withPermit {
+                        doRealWork(index)
                     }
                 }
             }
@@ -161,7 +165,19 @@ class ArchivePageLoader(
         false
     }
 
-    override fun preloadPages(pages: List<Int>, pair: Pair<Int, Int>) {}
+    override val preloadPageCount = 3
+
+    override fun preloadPages(pages: List<Int>, bounds: Pair<Int, Int>) {
+        synchronized(mJobMap) {
+            val (min, max) = bounds
+            mJobMap.forEach { (i, job) ->
+                if (i < min || i > max) {
+                    job.cancel()
+                }
+            }
+            pages.forEach(::enqueue)
+        }
+    }
 }
 
 private const val DEBUG_TAG = "ArchivePageLoader"

app/src/main/kotlin/com/hippo/ehviewer/gallery/EhPageLoader.kt

@@ -15,6 +15,7 @@
  */
 package com.hippo.ehviewer.gallery
 
+import com.hippo.ehviewer.Settings
 import com.hippo.ehviewer.client.EhUtils
 import com.hippo.ehviewer.client.data.GalleryInfo
 import com.hippo.ehviewer.image.Image
@@ -105,7 +106,9 @@ class EhPageLoader(private val mGalleryInfo: GalleryInfo, startPage: Int) :
         notifyPageFailed(index, error)
     }
 
-    override fun preloadPages(pages: List<Int>, pair: Pair<Int, Int>) {
-        mSpiderQueen.preloadPages(pages, pair)
+    override val preloadPageCount = Settings.preloadImage
+
+    override fun preloadPages(pages: List<Int>, bounds: Pair<Int, Int>) {
+        mSpiderQueen.preloadPages(pages, bounds)
     }
 }

app/src/main/kotlin/com/hippo/ehviewer/ui/reader/PagerItem.kt

@@ -45,13 +45,13 @@ fun PagerItem(
     contentScale: ContentScale,
     modifier: Modifier = Modifier,
 ) {
+    LaunchedEffect(Unit) {
+        pageLoader.request(page.index)
+    }
     val defaultError = stringResource(id = R.string.decode_image_error)
     val state by page.status.collectAsState()
     when (state) {
         Page.State.QUEUE, Page.State.LOAD_PAGE, Page.State.DOWNLOAD_IMAGE -> {
-            LaunchedEffect(Unit) {
-                pageLoader.request(page.index)
-            }
             Box(
                 modifier = Modifier.fillMaxWidth().aspectRatio(DEFAULT_ASPECT),
                 contentAlignment = Alignment.Center,

app/src/main/kotlin/eu/kanade/tachiyomi/ui/reader/loader/PageLoader.kt

@@ -33,7 +33,7 @@ abstract class PageLoader {
         (0 until size).map { ReaderPage(it) }
     }
 
-    private val preloads = com.hippo.ehviewer.Settings.preloadImage.coerceIn(0, 100)
+    abstract val preloadPageCount: Int
 
     @CallSuper
     open suspend fun awaitReady(): Boolean {
@@ -66,11 +66,11 @@ abstract class PageLoader {
             onRequest(index)
         }
 
-        val pagesAbsent = ((index - 5).coerceAtLeast(0) until (preloads + index).coerceAtMost(size))
-            .mapNotNullTo(mutableListOf()) { it.takeIf { it != index && cache[it] == null } }
+        val preloadRange = (index - 3).coerceAtLeast(0) until (index + preloadPageCount).coerceAtMost(size)
+        val pagesAbsent = preloadRange.mapNotNullTo(mutableListOf()) { it.takeIf { it != index && cache[it] == null } }
         // Load forward first, then load backward from the nearest index
         pagesAbsent.sortBy { (index - it).coerceAtLeast(0) }
-        preloadPages(pagesAbsent, (index - 10).coerceAtLeast(0) to (preloads + index + 10).coerceAtMost(size))
+        preloadPages(pagesAbsent, (preloadRange.first - 5).coerceAtLeast(0) to (preloadRange.last + 10).coerceAtMost(size))
     }
 
     fun retryPage(index: Int, orgImg: Boolean = false) {
@@ -78,7 +78,7 @@ abstract class PageLoader {
         onForceRequest(index, orgImg)
     }
 
-    protected abstract fun preloadPages(pages: List<Int>, pair: Pair<Int, Int>)
+    protected abstract fun preloadPages(pages: List<Int>, bounds: Pair<Int, Int>)
 
     protected abstract fun onRequest(index: Int)