try improving the image loading performance on weaker devices

app/src/main/kotlin/com/simplemobiletools/gallery/pro/fragments/PhotoFragment.kt

@@ -251,7 +251,6 @@ class PhotoFragment : ViewPagerFragment() {
 
     override fun onConfigurationChanged(newConfig: Configuration) {
         super.onConfigurationChanged(newConfig)
-
         if (!mWasInit) {
             return
         }
@@ -272,6 +271,7 @@ class PhotoFragment : ViewPagerFragment() {
             loadImage()
         }
 
+        measureScreen()
         initExtendedDetails()
         updateInstantSwitchWidths()
     }
@@ -461,13 +461,14 @@ class PhotoFragment : ViewPagerFragment() {
         mIsSubsamplingVisible = true
         val config = context!!.config
         val showHighestQuality = config.showHighestQuality
+        val minTileDpi = if (showHighestQuality) -1 else getMinTileDpi()
 
         val bitmapDecoder = object : DecoderFactory<ImageDecoder> {
             override fun make() = PicassoDecoder(mMedium.path, Picasso.get(), rotation)
         }
 
         val regionDecoder = object : DecoderFactory<ImageRegionDecoder> {
-            override fun make() = PicassoRegionDecoder(showHighestQuality)
+            override fun make() = PicassoRegionDecoder(showHighestQuality, mScreenWidth, mScreenHeight, minTileDpi)
         }
 
         var newOrientation = (rotation + mCurrentRotationDegrees) % 360
@@ -477,7 +478,7 @@ class PhotoFragment : ViewPagerFragment() {
 
         mView.subsampling_view.apply {
             setMaxTileSize(if (showHighestQuality) Integer.MAX_VALUE else 4096)
-            setMinimumTileDpi(if (showHighestQuality) -1 else getMinTileDpi())
+            setMinimumTileDpi(minTileDpi)
             background = ColorDrawable(Color.TRANSPARENT)
             bitmapDecoderFactory = bitmapDecoder
             regionDecoderFactory = regionDecoder
@@ -487,6 +488,7 @@ class PhotoFragment : ViewPagerFragment() {
             isOneToOneZoomEnabled = config.allowOneToOneZoom
             orientation = newOrientation
             setImage(mMedium.path)
+
             onImageEventListener = object : SubsamplingScaleImageView.OnImageEventListener {
                 override fun onReady() {
                     background = ColorDrawable(if (config.blackBackground) Color.BLACK else config.backgroundColor)
@@ -520,10 +522,10 @@ class PhotoFragment : ViewPagerFragment() {
         val averageDpi = (metrics.xdpi + metrics.ydpi) / 2
         val device = "${Build.BRAND} ${Build.MODEL}".toLowerCase()
         return when {
-            WEIRD_DEVICES.contains(device) -> 240
+            WEIRD_DEVICES.contains(device) -> WEIRD_TILE_DPI
-            averageDpi > 400 -> 280
+            averageDpi > 400 -> HIGH_TILE_DPI
-            averageDpi > 300 -> 220
+            averageDpi > 300 -> NORMAL_TILE_DPI
-            else -> 160
+            else -> LOW_TILE_DPI
         }
     }
 

app/src/main/kotlin/com/simplemobiletools/gallery/pro/helpers/Constants.kt

@@ -208,3 +208,9 @@ const val MAX_VIDEO_ZOOM_SCALE = 5f
 const val ZOOM_MODE_NONE = 0
 const val ZOOM_MODE_DRAG = 1
 const val ZOOM_MODE_ZOOM = 2
+
+// constants related to image quality
+const val LOW_TILE_DPI = 160
+const val NORMAL_TILE_DPI = 220
+const val WEIRD_TILE_DPI = 240
+const val HIGH_TILE_DPI = 280

app/src/main/kotlin/com/simplemobiletools/gallery/pro/helpers/PicassoRegionDecoder.kt

@@ -5,7 +5,7 @@ import android.graphics.*
 import android.net.Uri
 import com.davemorrissey.labs.subscaleview.ImageRegionDecoder
 
-class PicassoRegionDecoder(val showHighestQuality: Boolean) : ImageRegionDecoder {
+class PicassoRegionDecoder(val showHighestQuality: Boolean, val screenWidth: Int, val screenHeight: Int, val minTileDpi: Int) : ImageRegionDecoder {
     private var decoder: BitmapRegionDecoder? = null
     private val decoderLock = Any()
 
@@ -18,10 +18,20 @@ class PicassoRegionDecoder(val showHighestQuality: Boolean) : ImageRegionDecoder
 
     override fun decodeRegion(rect: Rect, sampleSize: Int): Bitmap {
         synchronized(decoderLock) {
+            var newSampleSize = sampleSize
+            if (!showHighestQuality && minTileDpi == LOW_TILE_DPI) {
+                if ((rect.width() > rect.height() && screenWidth > screenHeight) || (rect.height() > rect.width() && screenHeight > screenWidth)) {
+                    if ((rect.width() / sampleSize > screenWidth || rect.height() / sampleSize > screenHeight)) {
+                        newSampleSize *= 2
+                    }
+                }
+            }
+
             val options = BitmapFactory.Options()
-            options.inSampleSize = sampleSize
+            options.inSampleSize = newSampleSize
             options.inPreferredConfig = if (showHighestQuality) Bitmap.Config.ARGB_8888 else Bitmap.Config.RGB_565
             val bitmap = decoder!!.decodeRegion(rect, options)
+
             return bitmap ?: throw RuntimeException("Region decoder returned null bitmap - image format may not be supported")
         }
     }