cc/tiles/image_decode_cache.h

// Copyright 2015 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_IMAGE_DECODE_CACHE_H_
#define CC_TILES_IMAGE_DECODE_CACHE_H_

#include "base/memory/ref_counted.h"
#include "cc/base/devtools_instrumentation.h"
#include "cc/cc_export.h"
#include "cc/paint/decoded_draw_image.h"
#include "cc/paint/draw_image.h"
#include "cc/raster/tile_task.h"
#include "cc/tiles/image_decode_cache_utils.h"
#include "cc/tiles/tile_priority.h"

namespace cc {

// ImageDecodeCache is responsible for generating decode tasks, decoding
// images, storing images in cache, and being able to return the decoded images
// when requested.

// ImageDecodeCache is responsible for the following things:
// 1. Given a DrawImage, it can return an TileTask which when run will
//    decode and cache the resulting image. If the image does not need a task to
//    be decoded, then nullptr will be returned. The return value of the
//    function indicates whether the image was or is going to be locked, so an
//    unlock will be required.
// 2. Given a cache key and a DrawImage, it can decode the image and store it in
//    the cache. Note that it is important that this function is only accessed
//    via an image decode task.
// 3. Given a DrawImage, it can return a DecodedDrawImage, which represented the
//    decoded version of the image. Note that if the image is not in the cache
//    and it needs to be scaled/decoded, then this decode will happen as part of
//    getting the image. As such, this should only be accessed from a raster
//    thread.
class CC_EXPORT ImageDecodeCache {
 public:
  enum class TaskType { kInRaster, kOutOfRaster };

  // This information should be used strictly in tracing, UMA, and any other
  // reporting systems.
  struct TracingInfo {
    TracingInfo(uint64_t prepare_tiles_id,
                TilePriority::PriorityBin requesting_tile_bin,
                TaskType task_type)
        : prepare_tiles_id(prepare_tiles_id),
          requesting_tile_bin(requesting_tile_bin),
          task_type(task_type) {}
    TracingInfo() = default;

    // ID for the current prepare tiles call.
    const uint64_t prepare_tiles_id = 0;

    // The bin of the tile that caused this image to be requested.
    const TilePriority::PriorityBin requesting_tile_bin = TilePriority::NOW;

    // Whether the decode is requested as a part of tile rasterization.
    const TaskType task_type = TaskType::kInRaster;
  };

  static devtools_instrumentation::ScopedImageDecodeTask::TaskType
  ToScopedTaskType(TaskType task_type) {
    using ScopedTaskType =
        devtools_instrumentation::ScopedImageDecodeTask::TaskType;
    switch (task_type) {
      case TaskType::kInRaster:
        return ScopedTaskType::kInRaster;
      case TaskType::kOutOfRaster:
        return ScopedTaskType::kOutOfRaster;
    }
    NOTREACHED();
    return ScopedTaskType::kInRaster;
  }

  virtual ~ImageDecodeCache() {}

  struct CC_EXPORT TaskResult {
    explicit TaskResult(bool need_unref);
    explicit TaskResult(scoped_refptr<TileTask> task);
    TaskResult(const TaskResult& result);
    ~TaskResult();

    bool IsAtRaster() const { return !task && !need_unref; }

    scoped_refptr<TileTask> task;
    bool need_unref = false;
  };
  // Fill in an TileTask which will decode the given image when run. In
  // case the image is already cached, fills in nullptr. Returns true if the
  // image needs to be unreffed when the caller is finished with it.
  //
  // This is called by the tile manager (on the compositor thread) when creating
  // a raster task.
  virtual TaskResult GetTaskForImageAndRef(const DrawImage& image,
                                           const TracingInfo& tracing_info) = 0;
  // Similar to GetTaskForImageAndRef, except that it returns tasks that are not
  // meant to be run as part of raster. That is, this is part of a predecode
  // API. Note that this should only return a task responsible for decoding (and
  // not uploading), since it will be run on a worker thread which may not have
  // the right GPU context for upload.
  virtual TaskResult GetOutOfRasterDecodeTaskForImageAndRef(
      const DrawImage& image) = 0;

  // Unrefs an image. When the tile is finished, this should be called for every
  // GetTaskForImageAndRef call that returned true.
  virtual void UnrefImage(const DrawImage& image) = 0;

  // Returns a decoded draw image. This may cause a decode if the image was not
  // predecoded.
  //
  // This is called by a raster task (on a worker thread) when an image is
  // required.
  //
  // TODO(khushalsagar/vmpstr): Since the cache knows if it's a video frame, it
  // should discard any frames from the same source not in use in the
  // compositor.
  virtual DecodedDrawImage GetDecodedImageForDraw(const DrawImage& image) = 0;
  // Unrefs an image. This should be called for every GetDecodedImageForDraw
  // when the draw with the image is finished.
  virtual void DrawWithImageFinished(const DrawImage& image,
                                     const DecodedDrawImage& decoded_image) = 0;

  // This function informs the cache that now is a good time to clean up
  // memory. This is called periodically from the compositor thread.
  virtual void ReduceCacheUsage() = 0;

  // This function informs the cache that we are hidden and should not be
  // retaining cached resources longer than needed.
  virtual void SetShouldAggressivelyFreeResources(
      bool aggressively_free_resources) = 0;

  // Clears all elements from the cache.
  virtual void ClearCache() = 0;

  // Returns the maximum amount of memory we would be able to lock. This ignores
  // any temporary states, such as throttled, and return the maximum possible
  // memory. It is used as an esimate of whether an image can fit into the
  // locked budget before creating a task.
  virtual size_t GetMaximumMemoryLimitBytes() const = 0;

  // Returns true if the cache should be used for |image|. In certain cases the
  // image can directly be used for raster (for instance bitmaps in a software
  // draw).
  virtual bool UseCacheForDrawImage(const DrawImage& image) const = 0;

 protected:
  void RecordImageMipLevelUMA(int mip_level);
};

}  // namespace cc

#endif  // CC_TILES_IMAGE_DECODE_CACHE_H_