Photo Picker Dialog: Add caching for the decoded images.

chrome/android/java/src/org/chromium/chrome/browser/photo_picker/PickerBitmapViewHolder.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.graphics.Bitmap;
 import android.graphics.Canvas;
 import android.graphics.Color;
 import android.graphics.Paint;
@@ skipping 27 matching lines @@
     /**
      * The notification handler for when an image has been decoded.
      * @param filePath The file path for the newly decoded image.
      * @param bitmap The results of the decoding (or placeholder image, if failed).
      */
     public void imageDecodedCallback(String filePath, Bitmap bitmap) {
         if (bitmap == null || bitmap.getWidth() == 0 || bitmap.getHeight() == 0) {
             return;
         }
 
+        if (mCategoryView.getHighResBitmaps().get(filePath) == null) {
+            mCategoryView.getHighResBitmaps().put(filePath, bitmap);

[Michael van Ouwerkerk, 2017/04/27 17:07:34]

The documentation for this param says it might be a placeholder image on
failure. Should that be stored in the cache?

[Finnur, 2017/05/04 16:05:15]

That changed with the latest sync. Decoding will not return a placeholder image
on failure any longer (just a null bitmap).

+        }
+
+        if (mCategoryView.getLowResBitmaps().get(filePath) == null) {
+            // Scaling the image down takes between 0-1 ms on average (Nexus 6 phone debug build).
+            Bitmap lowres = BitmapUtils.scale(bitmap, 40, false);

[Michael van Ouwerkerk, 2017/04/27 17:07:34]

What's 40? Px? Dp? Maybe extract a documented constant.

[Finnur, 2017/05/04 16:05:15]

Done.

+            mCategoryView.getLowResBitmaps().put(filePath, lowres);
+        }
+
         if (!TextUtils.equals(mBitmapDetails.getFilePath(), filePath)) {
             return;
         }
 
         mItemView.setThumbnailBitmap(bitmap);
     }
 
     /**
      * Display a single item from |position| in the PickerCategoryView.
      * @param categoryView The PickerCategoryView to use to fetch the image.
      * @param position The position of the item to fetch.
      */
     public void displayItem(PickerCategoryView categoryView, int position) {
         mCategoryView = categoryView;
 
         List<PickerBitmap> pickerBitmaps = mCategoryView.getPickerBitmaps();
         mBitmapDetails = pickerBitmaps.get(position);
 
         if (mBitmapDetails.type() == PickerBitmap.CAMERA
                 || mBitmapDetails.type() == PickerBitmap.GALLERY) {
             mItemView.initializeSpecialTile(mBitmapDetails);
             return;
         }
 
-        // TODO(finnur): Use cached image, if available.
+        String filePath = mBitmapDetails.getFilePath();
+        Bitmap original = mCategoryView.getHighResBitmaps().get(filePath);
+        if (original != null) {
+            mItemView.initialize(mBitmapDetails, original, false);
+            return;
+        }
+
+        int size = mCategoryView.getImageSize();
+        Bitmap placeholder = mCategoryView.getLowResBitmaps().get(filePath);
+        if (placeholder != null) {
+            // Scaling the image up takes between 3-4 ms on average (Nexus 6 phone debug build).
+            placeholder = BitmapUtils.scale(placeholder, size, false);
+            mItemView.initialize(mBitmapDetails, placeholder, true);
+        } else {
+            mItemView.initialize(mBitmapDetails, null, true);
+        }
 
         // TODO(finnur): Use decoder instead.
-        int size = mCategoryView.getImageSize();
         imageDecodedCallback(mBitmapDetails.getFilePath(), createPlaceholderBitmap(size, size));
     }
 
     /**
      * Creates a placeholder bitmap.
      * @param width The requested width of the resulting bitmap.
      * @param height The requested height of the resulting bitmap.
      * @return Placeholder bitmap.
      */
     // TODO(finnur): Remove once the decoder is in place.
     private Bitmap createPlaceholderBitmap(int width, int height) {
         Bitmap placeholder = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
         Canvas canvas = new Canvas(placeholder);
         Paint paint = new Paint();
         paint.setColor(Color.GRAY);
         canvas.drawRect(0, 0, (float) width, (float) height, paint);
         return placeholder;
     }
 
     /**
      * Returns the file path of the current request.
      */
     public String getFilePath() {
         return mBitmapDetails == null ? null : mBitmapDetails.getFilePath();
     }
 }