Add toggle to invert page color in reader color filter settings (#5713)

(cherry picked from commit 4c8dfd0c0c)

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

@@ -55,6 +55,8 @@ object PreferenceKeys {
 
     const val grayscale = "pref_grayscale"
 
+    const val invertedColors = "pref_inverted_colors"
+
     const val defaultReadingMode = "pref_default_reading_mode_key"
 
     const val defaultOrientationType = "pref_default_orientation_type_key"

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

@@ -133,6 +133,8 @@ class PreferencesHelper(val context: Context) {
 
     fun grayscale() = flowPrefs.getBoolean(Keys.grayscale, false)
 
+    fun invertedColors() = flowPrefs.getBoolean(Keys.invertedColors, false)
+
     fun defaultReadingMode() = prefs.getInt(Keys.defaultReadingMode, ReadingModeType.RIGHT_TO_LEFT.flagValue)
 
     fun defaultOrientationType() = prefs.getInt(Keys.defaultOrientationType, OrientationType.FREE.flagValue)

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

@@ -100,6 +100,7 @@ import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.MutableSharedFlow
 import kotlinx.coroutines.flow.drop
 import kotlinx.coroutines.flow.launchIn
+import kotlinx.coroutines.flow.merge
 import kotlinx.coroutines.flow.onEach
 import kotlinx.coroutines.flow.sample
 import kotlinx.coroutines.launch
@@ -1466,11 +1467,25 @@ class ReaderActivity : BaseRxActivity<ReaderActivityBinding, ReaderPresenter>()
      */
     private inner class ReaderConfig {
 
-        private val grayscalePaint by lazy {
-            Paint().apply {
+        private fun getCombinedPaint(grayscale: Boolean, invertedColors: Boolean): Paint {
+            return Paint().apply {
                 colorFilter = ColorMatrixColorFilter(
                     ColorMatrix().apply {
-                        setSaturation(0f)
+                        if (grayscale) {
+                            setSaturation(0f)
+                        }
+                        if (invertedColors) {
+                            postConcat(
+                                ColorMatrix(
+                                    floatArrayOf(
+                                        -1f, 0f, 0f, 0f, 255f,
+                                        0f, -1f, 0f, 0f, 255f,
+                                        0f, 0f, -1f, 0f, 255f,
+                                        0f, 0f, 0f, 1f, 0f
+                                    )
+                                )
+                            )
+                        }
                     }
                 )
             }
@@ -1523,8 +1538,8 @@ class ReaderActivity : BaseRxActivity<ReaderActivityBinding, ReaderPresenter>()
                 .onEach { setColorFilter(preferences.colorFilter().get()) }
                 .launchIn(lifecycleScope)
 
-            preferences.grayscale().asFlow()
-                .onEach { setGrayscale(it) }
+            merge(preferences.grayscale().asFlow(), preferences.invertedColors().asFlow())
+                .onEach { setLayerPaint(preferences.grayscale().get(), preferences.invertedColors().get()) }
                 .launchIn(lifecycleScope)
 
             preferences.fullscreen().asFlow()
@@ -1675,8 +1690,8 @@ class ReaderActivity : BaseRxActivity<ReaderActivityBinding, ReaderPresenter>()
             binding.colorOverlay.setFilterColor(value, preferences.colorFilterMode().get())
         }
 
-        private fun setGrayscale(enabled: Boolean) {
-            val paint = if (enabled) grayscalePaint else null
+        private fun setLayerPaint(grayscale: Boolean, invertedColors: Boolean) {
+            val paint = if (grayscale || invertedColors) getCombinedPaint(grayscale, invertedColors) else null
             binding.viewerContainer.setLayerType(LAYER_TYPE_HARDWARE, paint)
         }
     }

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

@@ -67,6 +67,7 @@ class ReaderColorFilterSettings @JvmOverloads constructor(context: Context, attr
         binding.customBrightness.bindToPreference(preferences.customBrightness())
         binding.colorFilterMode.bindToPreference(preferences.colorFilterMode())
         binding.grayscale.bindToPreference(preferences.grayscale())
+        binding.invertedColors.bindToPreference(preferences.invertedColors())
 
         binding.seekbarColorFilterAlpha.setOnSeekBarChangeListener(
             object : SimpleSeekBarListener() {