Photo Picker Dialog: Add caching for the decoded images.

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

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 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;
 import android.widget.RelativeLayout;
 
 import org.chromium.chrome.R;
 import org.chromium.chrome.browser.widget.selection.SelectableListLayout;
 import org.chromium.chrome.browser.widget.selection.SelectionDelegate;
 import org.chromium.ui.PhotoPickerListener;
 
 import java.util.Arrays;
 import java.util.List;
 
 /**
  * A class for keeping track of common data associated with showing photos in
  * the photo picker, for example the RecyclerView and the bitmap caches.
  */
 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;
 
     // The view containing the RecyclerView and the toolbar, etc.
     private SelectableListLayout<PickerBitmap> mSelectableListLayout;
 
     // Our context.
     private Context mContext;
 
     // The list of images on disk, sorted by last-modified first.
@@ skipping 10 matching lines @@
 
     // The RecyclerView showing the images.
     private RecyclerView mRecyclerView;
 
     // The {@link PickerAdapter} for the RecyclerView.
     private PickerAdapter mPickerAdapter;
 
     // 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
      * are a mix).
      */
     private int mColumns;
 
     // The padding between columns. See also comment for mColumns.
     private int mPadding;
 
@@ skipping 38 matching lines @@
 
         Rect appRect = new Rect();
         ((Activity) context).getWindow().getDecorView().getWindowVisibleDisplayFrame(appRect);
         calculateGridMetrics(appRect.width());
 
         RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(mContext, mColumns);
         mRecyclerView.setHasFixedSize(true);
         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;
+            }
+        };
     }
 
     /**
      * Severs the connection to the decoding utility process and cancels any outstanding requests.
      */
     public void onDialogDismissed() {
         if (mWorkerTask != null) {
             mWorkerTask.cancel(true);
             mWorkerTask = null;
         }
@@ skipping 83 matching lines @@
     }
 
     public List<PickerBitmap> getPickerBitmaps() {
         return mPickerBitmaps;
     }
 
     public DecoderServiceHost getDecoderServiceHost() {
         return mDecoderServiceHost;
     }
 
+    public LruCache<String, Bitmap> getLowResBitmaps() {
+        return mLowResBitmaps;
+    }
+
+    public LruCache<String, Bitmap> getHighResBitmaps() {
+        return mHighResBitmaps;
+    }
+
     public boolean isMultiSelectAllowed() {
         return mMultiSelectionAllowed;
     }
 
     /**
      * Notifies the listener that the user selected to launch the gallery.
      */
     public void showGallery() {
         mListener.onPickerUserAction(PhotoPickerListener.Action.LAUNCH_GALLERY, null);
     }
@@ skipping 79 matching lines @@
                 if (position < mSpanCount) {
                     top = mSpacing;
                 }
                 bottom = mSpacing;
             }
 
             outRect.set(left, top, right, bottom);
         }
     }
 }