Photo Picker Dialog: Add caching for the decoded images.

chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerCategoryView.java

Index: chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerCategoryView.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerCategoryView.java b/chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerCategoryView.java
index bbabd8086d38e6ce862d7c50e04f1a1f17e3f6f4..ea98c4d2745ba310a3fd397abd95b821863d646e 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerCategoryView.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerCategoryView.java
@@ -6,10 +6,12 @@ package org.chromium.chrome.browser.photo_picker;
 
 import android.app.Activity;
 import android.content.Context;
+import android.graphics.Bitmap;
 import android.graphics.Rect;
 import android.support.v7.widget.GridLayoutManager;
 import android.support.v7.widget.RecyclerView;
 import android.support.v7.widget.Toolbar.OnMenuItemClickListener;
+import android.util.LruCache;
 import android.view.LayoutInflater;
 import android.view.MenuItem;
 import android.view.View;
@@ -30,6 +32,8 @@ import java.util.List;
 public class PickerCategoryView extends RelativeLayout
         implements FileEnumWorkerTask.FilesEnumeratedCallback, RecyclerView.RecyclerListener,
                    DecoderServiceHost.ServiceReadyCallback, OnMenuItemClickListener {
+    private static final int KILOBYTE = 1024;
+
     // The dialog that owns us.
     private PhotoPickerDialog mDialog;
 
@@ -60,6 +64,14 @@ public class PickerCategoryView extends RelativeLayout
     // The {@link SelectionDelegate} keeping track of which images are selected.
     private SelectionDelegate<PickerBitmap> mSelectionDelegate;
 
+    // A low-resolution cache for images. Helpful for cache misses from the high-resolution cache
+    // to avoid showing gray squares (we show pixelated versions instead until image can be loaded
+    // off disk, which is much less jarring).
+    private LruCache<String, Bitmap> mLowResBitmaps;
+
+    // A high-resolution cache for images.
+    private LruCache<String, Bitmap> mHighResBitmaps;
+
     /**
      * The number of columns to show. Note: mColumns and mPadding (see below) should both be even
      * numbers or both odd, not a mix (the column padding will not be of uniform thickness if they
@@ -118,7 +130,21 @@ public class PickerCategoryView extends RelativeLayout
         mRecyclerView.setLayoutManager(mLayoutManager);
         mRecyclerView.addItemDecoration(new GridSpacingItemDecoration(mColumns, mPadding));
 
-        // TODO(finnur): Implement caching.
+        final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / KILOBYTE);
+        final int cacheSizeLarge = maxMemory / 2; // 1/2 of the available memory.
+        final int cacheSizeSmall = maxMemory / 8; // 1/8th of the available memory.

[Theresa, 2017/05/04 16:53:13]

How many bitmaps can the small cache hold vs the large?

[Finnur, 2017/05/05 20:41:45]

On a Nexus 6 run on my test phone, this resulted in a cache of 128 MB for
high-res images and just under 32 MB for low-res images.

Each high-res image is 830 KB, so that cache can hold at most 157 images.
Each low-res image is 6 KB, so that's 5461 images it can hold.

On my Nexus 4, the large cache is 96 MB and 24 MB, respectively.

Each high-res image is 234K, for a max of 420 images.
Each low-res image is 2K, for a max of 12288 photos.

On my svelte device, the large cache is 24 MB and 6 Mb, respectively.

Each high-res image is 190K, for a max of 130 images.
Each low-res image is 1K, for a max of 6144 photos.

[Theresa, 2017/05/08 19:34:42]

Thank you for the detailed information!

+        mLowResBitmaps = new LruCache<String, Bitmap>(cacheSizeSmall) {
+            @Override
+            protected int sizeOf(String key, Bitmap bitmap) {

[Theresa, 2017/05/04 16:53:13]

What does this override do?

[Finnur, 2017/05/05 20:41:45]

It presents the size of the cache in KB, since that's a lot more useful metric
than number of items.

[Theresa, 2017/05/08 19:34:42]

I phrased my question poorly -- what is using this sizeOf() method? Is it just
for debugging or does overriding the sizeOf() method change how the cache
behaves?

[Finnur, 2017/05/09 11:53:56]

It is for debugging. Removed.

+                return bitmap.getByteCount() / KILOBYTE;
+            }
+        };
+        mHighResBitmaps = new LruCache<String, Bitmap>(cacheSizeLarge) {
+            @Override
+            protected int sizeOf(String key, Bitmap bitmap) {
+                return bitmap.getByteCount() / KILOBYTE;
+            }
+        };
     }
 
     /**
@@ -222,6 +248,14 @@ public class PickerCategoryView extends RelativeLayout
         return mDecoderServiceHost;
     }
 
+    public LruCache<String, Bitmap> getLowResBitmaps() {
+        return mLowResBitmaps;
+    }
+
+    public LruCache<String, Bitmap> getHighResBitmaps() {
+        return mHighResBitmaps;
+    }
+
     public boolean isMultiSelectAllowed() {
         return mMultiSelectionAllowed;
     }