[blimp] Add SkPicture caching support.

blimp/engine/renderer/blimp_engine_picture_cache.h

+// Copyright 2016 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 BLIMP_ENGINE_RENDERER_BLIMP_ENGINE_PICTURE_CACHE_H_
+#define BLIMP_ENGINE_RENDERER_BLIMP_ENGINE_PICTURE_CACHE_H_
+
+#include <memory>
+#include <unordered_map>
+#include <vector>
+
+#include "base/macros.h"
+#include "blimp/common/compositor/reference_tracker.h"
+#include "cc/proto/picture_cache.h"
+#include "third_party/skia/include/core/SkPicture.h"
+
+class SkPixelSerializer;
+
+namespace blimp {
+namespace engine {
+
+// BlimpEnginePictureCache provides functionality for caching SkPictures before
+// they are sent from the engine to the client. The cache is cleared after
+// every time it is flushed which happens when CalculateCacheUpdateAndFlush()
+// is called. The expected state of what the client already has cached is
+// tracked. It is required to update this cache when an SkPicture
+// starts being used and when it is not longer in use by calling
+// MarkPictureForRegistration and MarkPictureForUnregistration respectively.
+// The lifetime of a cache matches the lifetime of a specific compositor.

[Kevin M, 2016/06/11 00:29:33]

What's the threading situation like for this class? Does this need to do
anything tricky to handle concurrent modifications by multiple raster threads?

[nyquist, 2016/06/14 01:37:57]

Only ever on the main thread. Added a comment to clarify that.

Do you think I should add a DCHECK() for that in all the public methods?

+class BlimpEnginePictureCache : public cc::EnginePictureCache {
+ public:
+  explicit BlimpEnginePictureCache(SkPixelSerializer* pixel_serializer);
+  ~BlimpEnginePictureCache() override;
+
+  // cc::EnginePictureCache implementation.
+  void MarkPictureForUnregistration(const SkPicture* picture) override;
+  void MarkPictureForRegistration(const SkPicture* picture) override;
+  cc::PictureCacheUpdate CalculateCacheUpdateAndFlush() override;
+
+ private:
+  // Serializes the SkPicture and adds it to |pictures_|.
+  void SerializePictureAndAddToCache(const SkPicture* picture);
+
+  // Returns whether |pictures_| currently contains the |picture|.
+  bool CacheContainsPicture(const SkPicture* picture);

[Kevin M, 2016/06/11 00:29:33]

nit: make this const?

[nyquist, 2016/06/14 01:37:57]

Done.

+
+  // A serializer that be used to pass in to SkPicture::serialize(...) for
+  // serializing the SkPicture to a stream.
+  SkPixelSerializer* pixel_serializer_;
+
+  // The current cache of pictures. Used for temporarily storing pictures until
+  // the next call to CalculateCacheUpdateAndFlush(), at which point this map
+  // is cleared.
+  std::unordered_map<uint32_t, cc::PictureData> pictures_;
+
+  // The reference tracker maintains the reference count of used SkPictures.
+  ReferenceTracker reference_tracker_;
+
+  DISALLOW_COPY_AND_ASSIGN(BlimpEnginePictureCache);
+};
+
+}  // namespace engine
+}  // namespace blimp
+
+#endif  // BLIMP_ENGINE_RENDERER_BLIMP_ENGINE_PICTURE_CACHE_H_