Center padding option for Surface Duos/other foldables (#634)

* Add center margin option for horizontal dual page view

* Update readme to make the point of the fork obvious

* Center margins now added to large single images that would display in place of two smaller pages

* Cleanup; reworked preference into an int selector to specify which margins to add

* Suggested fixes and and readme reversion which somehow got skipped last commit

* Missed the build block in readme. Oops.

README.md

@@ -85,8 +85,8 @@ Please make sure to read the full guidelines. Your issue may be closed without w
 <details><summary>Bugs</summary>
 
 * Include version (More → About → Version)
- * If not latest, try updating, it may have already been solved
- * Preview version is equal to the number of commits as seen in the main page
+* If not latest, try updating, it may have already been solved
+* Preview version is equal to the number of commits as seen in the main page
 * Include steps to reproduce (if not obvious from description)
 * Include screenshot (if needed)
 * If it could be device-dependent, try reproducing on another device (if possible)
@@ -119,4 +119,4 @@ See [CODE_OF_CONDUCT.md](./CODE_OF_CONDUCT.md).
 ## FAQ
 
 [See our website.](https://tachiyomi.org/)
-You can also reach out to us on [Discord](https://discord.gg/tachiyomi).
+You can also reach out to us on [Discord](https://discord.gg/tachiyomi).

app/src/main/java/eu/kanade/tachiyomi/data/preference/PreferencesHelper.kt

@@ -517,5 +517,7 @@ class PreferencesHelper(val context: Context) {
 
     fun pageLayout() = flowPrefs.getInt("page_layout", PagerConfig.PageLayout.AUTOMATIC)
 
+    fun centerMarginType() = flowPrefs.getInt("center_margin_type", PagerConfig.CenterMarginType.NONE)
+
     fun invertDoublePages() = flowPrefs.getBoolean("invert_double_pages", false)
 }

app/src/main/java/eu/kanade/tachiyomi/ui/reader/ReaderPresenter.kt

@@ -856,7 +856,7 @@ class ReaderPresenter(
 
         return imageSaver.save(
             image = Image.Page(
-                inputStream = { ImageUtil.mergeBitmaps(imageBitmap, imageBitmap2, isLTR, bg) },
+                inputStream = { ImageUtil.mergeBitmaps(imageBitmap, imageBitmap2, isLTR, 0, bg) },
                 name = filename,
                 location = location,
             ),

app/src/main/java/eu/kanade/tachiyomi/ui/reader/setting/ReaderReadingModeSettings.kt

@@ -97,6 +97,7 @@ class ReaderReadingModeSettings @JvmOverloads constructor(context: Context, attr
         binding.pagerPrefsGroup.pageTransitionsPager.bindToPreference(preferences.pageTransitionsPager())
         binding.pagerPrefsGroup.pageLayout.bindToPreference(preferences.pageLayout())
         binding.pagerPrefsGroup.invertDoublePages.bindToPreference(preferences.invertDoublePages())
+        binding.pagerPrefsGroup.centerMarginType.bindToPreference(preferences.centerMarginType())
         // SY <--
     }
 

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

@@ -71,6 +71,9 @@ class PagerConfig(
 
     @ColorInt
     var pageCanvasColor = Color.WHITE
+
+    var centerMarginType = CenterMarginType.NONE
+
     // SY <--
 
     init {
@@ -150,6 +153,9 @@ class PagerConfig(
                 },
             )
 
+        preferences.centerMarginType()
+            .register({ centerMarginType = it }, { imagePropertyChangedListener?.invoke() })
+
         preferences.invertDoublePages()
             .register({ invertDoublePages = it && dualPageSplit == false }, { imagePropertyChangedListener?.invoke() })
         // SY <--
@@ -197,6 +203,13 @@ class PagerConfig(
         navigationModeChangedListener?.invoke()
     }
 
+    object CenterMarginType {
+        const val NONE = 0
+        const val DOUBLE_PAGE_CENTER_MARGIN = 1
+        const val WIDE_PAGE_CENTER_MARGIN = 2
+        const val DOUBLE_AND_WIDE_CENTER_MARGIN = 3
+    }
+
     object PageLayout {
         const val SINGLE_PAGE = 0
         const val DOUBLE_PAGES = 1

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

@@ -28,6 +28,7 @@ import java.io.BufferedInputStream
 import java.io.ByteArrayInputStream
 import java.io.InputStream
 import java.util.concurrent.TimeUnit
+import kotlin.math.max
 import kotlin.math.roundToInt
 
 /**
@@ -353,7 +354,18 @@ class PagerPageHolder(
     }
 
     private fun mergePages(imageStream: InputStream, imageStream2: InputStream?): InputStream {
-        imageStream2 ?: return imageStream
+        // Handle adding a center margin to wide images if requested
+        if (imageStream2 == null) {
+            if (imageStream is BufferedInputStream && ImageUtil.isWideImage(imageStream) &&
+                viewer.config.centerMarginType and PagerConfig.CenterMarginType.WIDE_PAGE_CENTER_MARGIN > 0 &&
+                !viewer.config.imageCropBorders
+            ) {
+                return ImageUtil.AddHorizontalCenterMargin(imageStream, getHeight(), context)
+            } else {
+                return imageStream
+            }
+        }
+
         if (page.fullPage) return imageStream
         if (ImageUtil.isAnimatedAndSupported(imageStream)) {
             page.fullPage = true
@@ -424,7 +436,12 @@ class PagerPageHolder(
 
         imageStream.close()
         imageStream2.close()
-        return ImageUtil.mergeBitmaps(imageBitmap, imageBitmap2, isLTR, viewer.config.pageCanvasColor) {
+
+        val centerMargin = if (viewer.config.centerMarginType and PagerConfig.CenterMarginType.DOUBLE_PAGE_CENTER_MARGIN > 0 &&
+            !viewer.config.imageCropBorders
+        ) 96 / (max(1, getHeight()) / max(height, height2)) else 0
+
+        return ImageUtil.mergeBitmaps(imageBitmap, imageBitmap2, isLTR, centerMargin, viewer.config.pageCanvasColor) {
             viewer.scope.launchUI {
                 if (it == 100) {
                     progressIndicator.hide()
@@ -461,7 +478,11 @@ class PagerPageHolder(
             }
         }
 
-        return ImageUtil.splitInHalf(imageStream, side)
+        val sideMargin = if ((viewer.config.centerMarginType and PagerConfig.CenterMarginType.DOUBLE_PAGE_CENTER_MARGIN) > 0 &&
+            viewer.config.doublePages && !viewer.config.imageCropBorders
+        ) 48 else 0
+
+        return ImageUtil.splitInHalf(imageStream, side, sideMargin)
     }
 
     private fun onPageSplit(page: ReaderPage) {

app/src/main/java/eu/kanade/tachiyomi/ui/setting/SettingsReaderController.kt

@@ -508,6 +508,18 @@ class SettingsReaderController : SettingsController() {
                 titleRes = R.string.invert_double_pages
                 visibleIf(preferences.pageLayout()) { it != PagerConfig.PageLayout.SINGLE_PAGE }
             }
+
+            intListPreference {
+                bindTo(preferences.centerMarginType())
+                titleRes = R.string.center_margin
+                entriesRes = arrayOf(
+                    R.string.center_margin_none,
+                    R.string.center_margin_double_page,
+                    R.string.center_margin_wide_page,
+                    R.string.center_margin_double_and_wide_page,
+                )
+                entryValues = arrayOf("0", "1", "2", "3")
+            }
         }
         // SY <--
     }

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

@@ -1,5 +1,4 @@
 package eu.kanade.tachiyomi.util.system
-
 import android.content.Context
 import android.content.res.Configuration
 import android.graphics.Bitmap
@@ -128,16 +127,16 @@ object ImageUtil {
     /**
      * Extract the 'side' part from imageStream and return it as InputStream.
      */
-    fun splitInHalf(imageStream: InputStream, side: Side): InputStream {
+    fun splitInHalf(imageStream: InputStream, side: Side, sidePadding: Int): 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 singlePage = Rect(0, 0, width / 2 + sidePadding, height)
 
-        val half = createBitmap(width / 2, height)
+        val half = createBitmap(width / 2 + sidePadding, height)
         val part = when (side) {
             Side.RIGHT -> Rect(width - width / 2, 0, width, height)
             Side.LEFT -> Rect(0, 0, width / 2, height)
@@ -152,7 +151,8 @@ object ImageUtil {
     }
 
     /**
-     * Split the image into left and right parts, then merge them into a new image.
+     * Split the image into left and right parts, then merge them into a
+     * new vertically-aligned image.
      */
     fun splitAndMerge(imageStream: InputStream, upperSide: Side): InputStream {
         val imageBytes = imageStream.readBytes()
@@ -187,6 +187,40 @@ object ImageUtil {
     enum class Side {
         RIGHT, LEFT
     }
+    // SY -->
+    /**
+     * Split the image into left and right parts, then merge them into a
+     * new image with added center padding scaled relative to the height of the display view
+     * to compensate for scaling.
+     */
+
+    fun AddHorizontalCenterMargin(imageStream: InputStream, viewHeight: Int, backgroundContext: Context): InputStream {
+        val imageBitmap = ImageDecoder.newInstance(imageStream)?.decode()!!
+        val height = imageBitmap.height
+        val width = imageBitmap.width
+
+        val centerPadding = 96 / (max(1, viewHeight) / height)
+
+        val leftSourcePart = Rect(0, 0, width / 2, height)
+        val rightSourcePart = Rect(width / 2, 0, width, height)
+        val leftTargetPart = Rect(0, 0, width / 2, height)
+        val rightTargetPart = Rect(width / 2 + centerPadding, 0, width + centerPadding, height)
+
+        val bgColor = chooseBackground(backgroundContext, imageStream)
+        bgColor.setBounds(width / 2, 0, width / 2 + centerPadding, height)
+        val result = createBitmap(width + centerPadding, height)
+
+        result.applyCanvas {
+            drawBitmap(imageBitmap, leftSourcePart, leftTargetPart, null)
+            drawBitmap(imageBitmap, rightSourcePart, rightTargetPart, null)
+            bgColor.draw(this)
+        }
+
+        val output = ByteArrayOutputStream()
+        result.compress(Bitmap.CompressFormat.JPEG, 100, output)
+        return ByteArrayInputStream(output.toByteArray())
+    }
+    // SY <--
 
     /**
      * Check whether the image is considered a tall image.
@@ -534,31 +568,37 @@ object ImageUtil {
         imageBitmap: Bitmap,
         imageBitmap2: Bitmap,
         isLTR: Boolean,
+        centerMargin: Int,
         @ColorInt background: Int = Color.WHITE,
+
         progressCallback: ((Int) -> Unit)? = null,
     ): ByteArrayInputStream {
         val height = imageBitmap.height
         val width = imageBitmap.width
         val height2 = imageBitmap2.height
         val width2 = imageBitmap2.width
+
         val maxHeight = max(height, height2)
-        val result = Bitmap.createBitmap(width + width2, max(height, height2), Bitmap.Config.ARGB_8888)
+
+        val result = Bitmap.createBitmap(width + width2 + centerMargin, max(height, height2), Bitmap.Config.ARGB_8888)
         val canvas = Canvas(result)
         canvas.drawColor(background)
         val upperPart = Rect(
-            if (isLTR) 0 else width2,
+            if (isLTR) 0 else width2 + centerMargin,
             (maxHeight - imageBitmap.height) / 2,
-            (if (isLTR) 0 else width2) + imageBitmap.width,
+            (if (isLTR) 0 else width2 + centerMargin) + imageBitmap.width,
             imageBitmap.height + (maxHeight - imageBitmap.height) / 2,
         )
+
         canvas.drawBitmap(imageBitmap, imageBitmap.rect, upperPart, null)
         progressCallback?.invoke(98)
         val bottomPart = Rect(
-            if (!isLTR) 0 else width,
+            if (!isLTR) 0 else width + centerMargin,
             (maxHeight - imageBitmap2.height) / 2,
-            (if (!isLTR) 0 else width) + imageBitmap2.width,
+            (if (!isLTR) 0 else width + centerMargin) + imageBitmap2.width,
             imageBitmap2.height + (maxHeight - imageBitmap2.height) / 2,
         )
+
         canvas.drawBitmap(imageBitmap2, imageBitmap2.rect, bottomPart, null)
         progressCallback?.invoke(99)
 

app/src/main/res/layout/reader_pager_settings.xml

@@ -116,6 +116,13 @@
         android:textColor="?android:attr/textColorSecondary"
         android:text="@string/invert_double_pages" />
 
+    <eu.kanade.tachiyomi.widget.MaterialSpinnerView
+        android:id="@+id/center_margin_type"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:entries="@array/center_margin_types"
+        app:title="@string/pref_center_margin" />
+
     <androidx.constraintlayout.widget.Group
         android:id="@+id/tapping_prefs_group"
         android:layout_width="wrap_content"

app/src/main/res/values/arrays_sy.xml

@@ -21,4 +21,11 @@
         <item>@string/double_pages</item>
         <item>@string/automatic_orientation</item>
     </string-array>
+
+    <string-array name="center_margin_types">
+        <item>@string/center_margin_none</item>
+        <item>@string/center_margin_double_page</item>
+        <item>@string/center_margin_wide_page</item>
+        <item>@string/center_margin_double_and_wide_page</item>
+    </string-array>
 </resources>

app/src/main/res/values/strings_sy.xml

@@ -314,6 +314,15 @@
     <string name="automatic_can_still_switch">While using automatic page layout, you can still switch between layouts while reading without overriding this setting</string>
     <string name="invert_double_pages">Invert double pages</string>
 
+    <!-- Center margin -->
+    <string name="center_margin">Center Margin</string>
+    <string name="center_margin_none">None</string>
+    <string name="center_margin_double_page">Add to double Page</string>
+    <string name="center_margin_wide_page">Add to wide Page</string>
+    <string name="center_margin_double_and_wide_page">Add to both</string>
+    <string name="pref_center_margin">Center margin type</string>
+    <string name="pref_center_margin_summary">Insert spacer to accommodate deadspace on foldable devices.</string>
+
     <!-- Manga Page -->
     <!-- Manga Info -->
     <string name="az_recommends">See Recommendations</string>