Maybe help with double page jankyness

app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/pager/PagerPageHolder.kt

@@ -26,6 +26,7 @@ import eu.kanade.tachiyomi.widget.ViewPagerAdapter
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.Job
+import kotlinx.coroutines.delay
 import logcat.LogPriority
 import rx.Observable
 import rx.Subscription
@@ -103,7 +104,6 @@ class PagerPageHolder(
     var extraStatus: Int = 0
     var progress: Int = 0
     var extraProgress: Int = 0
-    private var skipExtra = false
     var scope: CoroutineScope? = null
     // SY <--
 
@@ -374,12 +374,12 @@ class PagerPageHolder(
         if (page.fullPage) return imageStream
         if (ImageUtil.isAnimatedAndSupported(imageStream)) {
             page.fullPage = true
-            skipExtra = true
+            splitDoublePages()
             return imageStream
         } else if (ImageUtil.isAnimatedAndSupported(imageStream2)) {
             page.isolatedPage = true
             extraPage?.fullPage = true
-            skipExtra = true
+            splitDoublePages()
             return imageStream
         }
         val imageBytes = imageStream.readBytes()
@@ -389,7 +389,7 @@ class PagerPageHolder(
             imageStream2.close()
             imageStream.close()
             page.fullPage = true
-            skipExtra = true
+            splitDoublePages()
             logcat(LogPriority.ERROR, e) { "Cannot combine pages" }
             return imageBytes.inputStream()
         }
@@ -401,7 +401,7 @@ class PagerPageHolder(
             imageStream2.close()
             imageStream.close()
             page.fullPage = true
-            skipExtra = true
+            splitDoublePages()
             return imageBytes.inputStream()
         }
 
@@ -412,8 +412,8 @@ class PagerPageHolder(
             imageStream2.close()
             imageStream.close()
             extraPage?.fullPage = true
-            skipExtra = true
             page.isolatedPage = true
+            splitDoublePages()
             logcat(LogPriority.ERROR, e) { "Cannot combine pages" }
             return imageBytes.inputStream()
         }
@@ -426,7 +426,7 @@ class PagerPageHolder(
             imageStream.close()
             extraPage?.fullPage = true
             page.isolatedPage = true
-            skipExtra = true
+            splitDoublePages()
             return imageBytes.inputStream()
         }
         val isLTR = (viewer !is R2LPagerViewer).xor(viewer.config.invertDoublePages)
@@ -444,6 +444,16 @@ class PagerPageHolder(
         }
     }
 
+    private fun splitDoublePages() {
+        scope?.launchUI {
+            delay(100)
+            viewer.splitDoublePages(page)
+            if (extraPage?.fullPage == true || page.fullPage) {
+                extraPage = null
+            }
+        }
+    }
+
     private fun splitInHalf(imageStream: InputStream): InputStream {
         var side = when {
             viewer is L2RPagerViewer && page is InsertPage -> ImageUtil.Side.RIGHT

app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/pager/PagerViewer.kt

@@ -28,7 +28,7 @@ import kotlin.math.min
 @Suppress("LeakingThis")
 abstract class PagerViewer(val activity: ReaderActivity) : BaseViewer {
 
-    private val scope = MainScope()
+    val scope = MainScope()
 
     /**
      * View pager used by this viewer. It's abstract to implement L2R, R2L and vertical pagers on
@@ -167,7 +167,7 @@ abstract class PagerViewer(val activity: ReaderActivity) : BaseViewer {
     /**
      * Called when a new page (either a [ReaderPage] or [ChapterTransition]) is marked as active
      */
-    private fun onPageChange(position: Int) {
+    fun onPageChange(position: Int) {
         val page = adapter.joinedItems.getOrNull(position)
         if (page != null && currentPage != page) {
             val allowPreload = checkAllowPreload(page.first as? ReaderPage)
@@ -439,6 +439,10 @@ abstract class PagerViewer(val activity: ReaderActivity) : BaseViewer {
         adapter.pageToShift = page ?: adapter.joinedItems.getOrNull(pager.currentItem)?.first as? ReaderPage
     }
 
+    fun splitDoublePages(currentPage: ReaderPage) {
+        adapter.splitDoublePages(currentPage)
+    }
+
     fun getShiftedPage(): ReaderPage? = adapter.pageToShift
     // SY <--
 }

app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/pager/PagerViewerAdapter.kt

@@ -8,9 +8,11 @@ import eu.kanade.tachiyomi.ui.reader.model.ReaderChapter
 import eu.kanade.tachiyomi.ui.reader.model.ReaderPage
 import eu.kanade.tachiyomi.ui.reader.model.ViewerChapters
 import eu.kanade.tachiyomi.ui.reader.viewer.hasMissingChapters
+import eu.kanade.tachiyomi.util.lang.launchUI
 import eu.kanade.tachiyomi.util.system.createReaderThemeContext
 import eu.kanade.tachiyomi.util.system.logcat
 import eu.kanade.tachiyomi.widget.ViewPagerAdapter
+import kotlinx.coroutines.delay
 import kotlin.math.max
 
 /**
@@ -358,5 +360,25 @@ class PagerViewerAdapter(private val viewer: PagerViewer) : ViewPagerAdapter() {
         }
         viewer.pager.setCurrentItem(index, false)
     }
+
+    fun splitDoublePages(current: ReaderPage) {
+        val oldCurrent = joinedItems.getOrNull(viewer.pager.currentItem)
+        setJoinedItems(
+            oldCurrent?.second == current ||
+                (current.index + 1) < (
+                (
+                    oldCurrent?.second
+                        ?: oldCurrent?.first
+                    ) as? ReaderPage
+                )?.index ?: 0
+        )
+
+        // The listener may be removed when we split a page, so the ui may not have updated properly
+        // This case usually happens when we load a new chapter and the first 2 pages need to split og
+        viewer.scope.launchUI {
+            delay(100)
+            viewer.onPageChange(viewer.pager.currentItem)
+        }
+    }
     // SY <--
 }