PagerPageHolder: Move chooseBackground call to IO thread (#5737)

* ImageUtil.chooseBackground: Use built-in decoder

* PagerPageHolder: Move chooseBackground call to IO thread

Also move stuffs and reuse image stream as bytes

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

@@ -37,6 +37,7 @@ import rx.Observable
 import rx.Subscription
 import rx.android.schedulers.AndroidSchedulers
 import rx.schedulers.Schedulers
+import java.io.ByteArrayInputStream
 import java.io.InputStream
 import java.nio.ByteBuffer
 import java.util.concurrent.TimeUnit
@@ -258,31 +259,40 @@ class PagerPageHolder(
         unsubscribeReadImageHeader()
         val streamFn = page.stream ?: return
 
-        var openStream: InputStream? = null
         readImageHeaderSubscription = Observable
             .fromCallable {
                 val stream = streamFn().buffered(16)
-                openStream = process(item, stream)
-
-                ImageUtil.isAnimatedAndSupported(stream)
+                val itemStream = process(item, stream)
+                try {
+                    val streamBytes = itemStream.readBytes()
+                    val isAnimated = ImageUtil.isAnimatedAndSupported(stream)
+                    val background = if (!isAnimated && viewer.config.automaticBackground) {
+                        ByteArrayInputStream(streamBytes).use { bais ->
+                            ImageUtil.chooseBackground(context, bais)
+                        }
+                    } else {
+                        null
+                    }
+                    Triple(streamBytes, isAnimated, background)
+                } finally {
+                    stream.close()
+                    itemStream.close()
+                }
             }
             .subscribeOn(Schedulers.io())
             .observeOn(AndroidSchedulers.mainThread())
-            .doOnNext { isAnimated ->
-                if (!isAnimated) {
-                    initSubsamplingImageView().apply {
-                        if (viewer.config.automaticBackground) {
-                            background = ImageUtil.chooseBackground(context, openStream!!)
+            .doOnNext { (streamBytes, isAnimated, background) ->
+                ByteArrayInputStream(streamBytes).use { bais ->
+                    if (!isAnimated) {
+                        this.background = background
+                        initSubsamplingImageView().apply {
+                            setImage(ImageSource.inputStream(bais))
                         }
-                        setImage(ImageSource.inputStream(openStream!!))
+                    } else {
+                        initImageView().setImage(bais)
                     }
-                } else {
-                    initImageView().setImage(openStream!!)
                 }
             }
-            // Keep the Rx stream alive to close the input stream only when unsubscribed
-            .flatMap { Observable.never<Unit>() }
-            .doOnUnsubscribe { openStream?.close() }
             .subscribe({}, {})
     }
 

app/src/main/java/eu/kanade/tachiyomi/util/system/ImageUtil.kt

@@ -18,7 +18,6 @@ import androidx.core.graphics.green
 import androidx.core.graphics.red
 import tachiyomi.decoder.Format
 import tachiyomi.decoder.ImageDecoder
-import tachiyomi.decoder.ImageType
 import java.io.ByteArrayInputStream
 import java.io.ByteArrayOutputStream
 import java.io.InputStream
@@ -181,11 +180,9 @@ object ImageUtil {
      * Algorithm for determining what background to accompany a comic/manga page
      */
     fun chooseBackground(context: Context, imageStream: InputStream): Drawable {
-        imageStream.mark(imageStream.available() + 1)
-
-        val image = BitmapFactory.decodeStream(imageStream)
-
-        imageStream.reset()
+        val decoder = ImageDecoder.newInstance(imageStream)
+        val image = decoder?.decode()
+        decoder?.recycle()
 
         val whiteColor = Color.WHITE
         if (image == null) return ColorDrawable(whiteColor)