cc: Optimize decode scheduling for checker-images.

cc/tiles/checker_image_tracker.h

 // 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.
 
 #ifndef CC_TILES_CHECKER_IMAGE_TRACKER_H_
 #define CC_TILES_CHECKER_IMAGE_TRACKER_H_
 
 #include <unordered_map>
 #include <vector>
 
@@ skipping 19 matching lines @@
 // sync tree is activated.
 // Note: It is illegal to call TakeImagesToInvalidateOnSyncTree for the next
 // sync tree until the previous tree is activated.
 class CC_EXPORT CheckerImageTracker {
  public:
   CheckerImageTracker(ImageController* image_controller,
                       CheckerImageTrackerClient* client,
                       bool enable_checker_imaging);
   ~CheckerImageTracker();
 
-  // Given the |images| for a tile, filters the images which will be deferred
-  // asynchronously using the image decoded service, eliminating them from
-  // |images| adds them to the |checkered_images| set, so they can be skipped
-  // during the rasterization of this tile.
-  // The entries remaining in |images| are for images for which a cached decode
-  // from the image decode service is available, or which must be decoded before
-  // before this tile can be rasterized.
-  void FilterImagesForCheckeringForTile(std::vector<DrawImage>* images,
-                                        ImageIdFlatSet* checkered_images,
-                                        WhichTree tree);
+  // Returns true if the decode for |image| will be deferred to the image decode
+  // service and it should be be skipped during raster.
+  bool ShouldCheckerImage(const sk_sp<const SkImage>& image, WhichTree tree);
+
+  using ImageDecodeQueue = std::vector<sk_sp<const SkImage>>;
+  void ScheduleImageDecodeQueue(ImageDecodeQueue image_decode_queue);
 
   // Returns the set of images to invalidate on the sync tree.
   const ImageIdFlatSet& TakeImagesToInvalidateOnSyncTree();
 
   void DidActivateSyncTree();
 
  private:
   enum class DecodePolicy {
     // The image can be decoded asynchronously from raster. When set, the image
     // is always skipped during rasterization of content that includes this
     // image until it has been decoded using the decode service.
     ASYNC,
     // The image has been decoded asynchronously once and should now be
     // synchronously rasterized with the content.
     SYNC_DECODED_ONCE,
     // The image has been permanently vetoed from being decoded async.
     SYNC_PERMANENT,
   };
 
   void DidFinishImageDecode(ImageId image_id,
                             ImageController::ImageDecodeRequestId request_id,
                             ImageController::ImageDecodeResult result);
 
-  // Returns true if the decode for |image| will be deferred to the image decode
-  // service and it should be be skipped during raster.
-  bool ShouldCheckerImage(const sk_sp<const SkImage>& image, WhichTree tree);
-
-  void ScheduleImageDecodeIfNecessary(const sk_sp<const SkImage>& image);
+  // Called when the next request in the |image_decode_queue_| should be
+  // scheduled with the image decode service.
+  void ScheduleNextImageDecode();
 
   ImageController* image_controller_;
   CheckerImageTrackerClient* client_;
   const bool enable_checker_imaging_;
 
   // A set of images which have been decoded and are pending invalidation for
   // raster on the checkered tiles.
   ImageIdFlatSet images_pending_invalidation_;
 
   // A set of images which were invalidated on the current sync tree.
   ImageIdFlatSet invalidated_images_on_current_sync_tree_;
 
-  // A set of images which are currently pending decode from the image decode
-  // service.
-  // TODO(khushalsagar): This should be a queue that gets re-built each time we
-  // do a PrepareTiles? See crbug.com/689184.
-  ImageIdFlatSet pending_image_decodes_;
+  // The queue of images pending decode. We maintain a queue to ensure that the
+  // order in which images are decoded is aligned with the priority of the tiles
+  // dependent on these images.
+  ImageDecodeQueue image_decode_queue_;
+
+  // The currently outstanding image decode that has been scheduled with the
+  // decode service. There can be only one outstanding decode at a time.
+  sk_sp<const SkImage> outstanding_image_decode_;
 
   // A map of ImageId to its DecodePolicy.
   // TODO(khushalsagar): Limit the size of this set.
   // TODO(khushalsagar): Plumb navigation changes here to reset this. See
   // crbug.com/693228.
   std::unordered_map<ImageId, DecodePolicy> image_async_decode_state_;
 
   // A map of image id to image decode request id for images to be unlocked.
   std::unordered_map<ImageId, ImageController::ImageDecodeRequestId>
       image_id_to_decode_request_id_;
 
   base::WeakPtrFactory<CheckerImageTracker> weak_factory_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TILES_CHECKER_IMAGE_TRACKER_H_