Added dual page split setting (#4252)

* Add DualPageSplit option

* remove extra line

* Split double-page into two pages

* Remove !isAnimated check and add (ALPHA) to the label

* Fix missing insert pages

* Pager cleanup

* Add dual split to Webtoon and fix Vertical

* Fix L2R/R2L

* Add comments and refactor code in ImageUtil

* Use a simpler split solution in webtoon mode

Co-authored-by: weng <>
Co-authored-by: Andreas E <andreas.everos@gmail.com>

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

@@ -1,5 +1,11 @@
 package eu.kanade.tachiyomi.util.system
 
+import android.graphics.Bitmap
+import android.graphics.BitmapFactory
+import android.graphics.Canvas
+import android.graphics.Rect
+import java.io.ByteArrayInputStream
+import java.io.ByteArrayOutputStream
 import java.io.InputStream
 import java.net.URLConnection
 
@@ -68,4 +74,71 @@ object ImageUtil {
         GIF("image/gif", "gif"),
         WEBP("image/webp", "webp")
     }
+
+    /**
+     * Check whether the image is a double image (width > height), return the result and original stream
+     */
+    fun isDoublePage(imageStream: InputStream): Pair<Boolean, InputStream> {
+        val imageBytes = imageStream.readBytes()
+
+        val options = BitmapFactory.Options().apply { inJustDecodeBounds = true }
+        BitmapFactory.decodeByteArray(imageBytes, 0, imageBytes.size, options)
+
+        return Pair(options.outWidth > options.outHeight, ByteArrayInputStream(imageBytes))
+    }
+
+    /**
+     * Extract the 'side' part from imageStream and return it as InputStream.
+     */
+    fun splitInHalf(imageStream: InputStream, side: Side): InputStream {
+        val imageBytes = imageStream.readBytes()
+
+        val imageBitmap = BitmapFactory.decodeByteArray(imageBytes, 0, imageBytes.size)
+        val height = imageBitmap.height
+        val width = imageBitmap.width
+
+        val singlePage = Rect(0, 0, width / 2, height)
+
+        val half = Bitmap.createBitmap(width / 2, height, Bitmap.Config.ARGB_8888)
+        val part = when (side) {
+            Side.RIGHT -> Rect(width - width / 2, 0, width, height)
+            Side.LEFT -> Rect(0, 0, width / 2, height)
+        }
+        val canvas = Canvas(half)
+        canvas.drawBitmap(imageBitmap, part, singlePage, null)
+        val output = ByteArrayOutputStream()
+        half.compress(Bitmap.CompressFormat.JPEG, 100, output)
+
+        return ByteArrayInputStream(output.toByteArray())
+    }
+
+    /**
+     * Split the image into left and right parts, then merge them into a new image.
+     */
+    fun splitAndMerge(imageStream: InputStream): InputStream {
+        val imageBytes = imageStream.readBytes()
+
+        val imageBitmap = BitmapFactory.decodeByteArray(imageBytes, 0, imageBytes.size)
+        val height = imageBitmap.height
+        val width = imageBitmap.width
+
+        val result = Bitmap.createBitmap(width / 2, height * 2, Bitmap.Config.ARGB_8888)
+        val canvas = Canvas(result)
+        // right -> upper
+        val rightPart = Rect(width - width / 2, 0, width, height)
+        val upperPart = Rect(0, 0, width / 2, height)
+        canvas.drawBitmap(imageBitmap, rightPart, upperPart, null)
+        // left -> bottom
+        val leftPart = Rect(0, 0, width / 2, height)
+        val bottomPart = Rect(0, height, width / 2, height * 2)
+        canvas.drawBitmap(imageBitmap, leftPart, bottomPart, null)
+
+        val output = ByteArrayOutputStream()
+        result.compress(Bitmap.CompressFormat.JPEG, 100, output)
+        return ByteArrayInputStream(output.toByteArray())
+    }
+
+    enum class Side {
+        RIGHT, LEFT
+    }
 }