cc/tiles/checker_image_tracker.cc - chromium/src - Git at Google

 // 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.

 #include "cc/tiles/checker_image_tracker.h"

 #include "base/bind.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/stl_util.h"
 #include "base/trace_event/trace_event.h"

 namespace cc {
 namespace {
 // The enum for recording checker-imaging decision UMA metric. Keep this
 // consistent with the ordering in CheckerImagingDecision in enums.xml.
 // Note that this enum is used to back a UMA histogram so should be treated as
 // append only.
 enum class CheckerImagingDecision {
   kCanChecker = 0,

   // Animation State vetoes.
   kVetoedAnimatedImage = 1,
   kVetoedVideoFrame = 2,
   // TODO(vmpstr): 3 used to be kVetoedAnimationUnknown, remove it somehow?
   kVetoedMultipartImage = 4,

   // Load state vetoes.
   kVetoedPartiallyLoadedImage = 5,
   // TODO(vmpstr): 6 used to be kVetoedLoadStateUnknown, remove it somehow?

   // Size associated vetoes.
   kVetoedSmallerThanCheckeringSize = 7,
   kVetoedLargerThanCacheSize = 8,

   // Vetoed because checkering of images has been disabled.
   kVetoedForceDisable = 9,

   // 10 used to be kVetoedNotRequiredForActivation.

   // Sync was requested by the embedder.
   kVetoedSyncRequested = 11,

   kCheckerImagingDecisionCount
 };

 std::string ToString(PaintImage::Id paint_image_id,
                      CheckerImagingDecision decision) {
   std::ostringstream str;
   str << "paint_image_id[" << paint_image_id << "] decision["
       << static_cast<int>(decision) << "]";
   return str.str();
 }

 CheckerImagingDecision GetAnimationDecision(const PaintImage& image) {
   if (image.is_multipart())
     return CheckerImagingDecision::kVetoedMultipartImage;

   switch (image.animation_type()) {
     case PaintImage::AnimationType::ANIMATED:
       return CheckerImagingDecision::kVetoedAnimatedImage;
     case PaintImage::AnimationType::VIDEO:
       return CheckerImagingDecision::kVetoedVideoFrame;
     case PaintImage::AnimationType::STATIC:
       return CheckerImagingDecision::kCanChecker;
   }

   NOTREACHED();
   return CheckerImagingDecision::kCanChecker;
 }

 CheckerImagingDecision GetLoadDecision(const PaintImage& image) {
   switch (image.completion_state()) {
     case PaintImage::CompletionState::DONE:
       return CheckerImagingDecision::kCanChecker;
     case PaintImage::CompletionState::PARTIALLY_DONE:
       return CheckerImagingDecision::kVetoedPartiallyLoadedImage;
   }

   NOTREACHED();
   return CheckerImagingDecision::kCanChecker;
 }

 CheckerImagingDecision GetSizeDecision(const SkIRect& src_rect,
                                        size_t min_bytes,
                                        size_t max_bytes) {
   // Ideally we would use the original image rect here to estimate the decode
   // duration for this image. But in the case of sprites/atlases, where small
   // subsets of this image are used across multiple tiles, re-invalidating for
   // replacing these images can incur heavy raster cost. So we use the src_rect
   // here instead.
   // TODO(khushalsagar): May be we should look at the invalidation rect for an
   // image here to detect these cases instead?
   base::CheckedNumeric<size_t> checked_size = 4;
   checked_size *= src_rect.width();
   checked_size *= src_rect.height();
   size_t size = checked_size.ValueOrDefault(std::numeric_limits<size_t>::max());

   if (size < min_bytes)
     return CheckerImagingDecision::kVetoedSmallerThanCheckeringSize;
   else if (size > max_bytes)
     return CheckerImagingDecision::kVetoedLargerThanCacheSize;
   else
     return CheckerImagingDecision::kCanChecker;
 }

 CheckerImagingDecision GetCheckerImagingDecision(const PaintImage& image,
                                                  const SkIRect& src_rect,
                                                  size_t min_bytes,
                                                  size_t max_bytes) {
   CheckerImagingDecision decision = GetAnimationDecision(image);
   if (decision != CheckerImagingDecision::kCanChecker)
     return decision;

   decision = GetLoadDecision(image);
   if (decision != CheckerImagingDecision::kCanChecker)
     return decision;

   return GetSizeDecision(src_rect, min_bytes, max_bytes);
 }

 }  // namespace

 // static
 const int CheckerImageTracker::kNoDecodeAllowedPriority = -1;

 CheckerImageTracker::ImageDecodeRequest::ImageDecodeRequest(
     PaintImage paint_image,
     DecodeType type)
     : paint_image(std::move(paint_image)), type(type) {}

 CheckerImageTracker::CheckerImageTracker(ImageController* image_controller,
                                          CheckerImageTrackerClient* client,
                                          bool enable_checker_imaging,
                                          size_t min_image_bytes_to_checker)
     : image_controller_(image_controller),
       client_(client),
       enable_checker_imaging_(enable_checker_imaging),
       min_image_bytes_to_checker_(min_image_bytes_to_checker),
       weak_factory_(this) {}

 CheckerImageTracker::~CheckerImageTracker() = default;

 void CheckerImageTracker::SetNoDecodesAllowed() {
   decode_priority_allowed_ = kNoDecodeAllowedPriority;
 }

 void CheckerImageTracker::SetMaxDecodePriorityAllowed(DecodeType decode_type) {
   DCHECK_GT(decode_type, kNoDecodeAllowedPriority);
   DCHECK_GE(decode_type, decode_priority_allowed_);
   DCHECK_LE(decode_type, DecodeType::kLast);

   if (decode_priority_allowed_ == decode_type)
     return;
   decode_priority_allowed_ = decode_type;

   // This will start the next decode if applicable.
   ScheduleNextImageDecode();
 }

 void CheckerImageTracker::ScheduleImageDecodeQueue(
     ImageDecodeQueue image_decode_queue) {
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
                "CheckerImageTracker::ScheduleImageDecodeQueue");
 #if DCHECK_IS_ON()
   // The decodes in the queue should be prioritized correctly.
   DecodeType type = DecodeType::kRaster;
   for (const auto& image_request : image_decode_queue) {
     DCHECK_GE(image_request.type, type);
     type = image_request.type;
   }
 #endif

   image_decode_queue_ = std::move(image_decode_queue);
   ScheduleNextImageDecode();
 }

 const PaintImageIdFlatSet&
 CheckerImageTracker::TakeImagesToInvalidateOnSyncTree() {
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
                "CheckerImageTracker::TakeImagesToInvalidateOnSyncTree");
   DCHECK_EQ(invalidated_images_on_current_sync_tree_.size(), 0u)
       << "Sync tree can not be invalidated more than once";

   invalidated_images_on_current_sync_tree_.swap(images_pending_invalidation_);
   images_pending_invalidation_.clear();
   return invalidated_images_on_current_sync_tree_;
 }

 void CheckerImageTracker::DidActivateSyncTree() {
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
                "CheckerImageTracker::DidActivateSyncTree");
   for (auto image_id : invalidated_images_on_current_sync_tree_)
     image_id_to_decode_.erase(image_id);
   invalidated_images_on_current_sync_tree_.clear();
 }

 void CheckerImageTracker::ClearTracker(bool can_clear_decode_policy_tracking) {
   // Unlock all images and tracking for images pending invalidation. The
   // |images_invalidated_on_current_sync_tree_| will be cleared when the sync
   // tree is activated.
   //
   // Note that we assume that any images with DecodePolicy::ASYNC, which may be
   // checkered, are safe to stop tracking here and will either be re-checkered
   // and invalidated when the decode completes or be invalidated externally.
   // This is because the policy decision for checkering an image is based on
   // inputs received from a PaintImage in the DisplayItemList. The policy chosen
   // for a PaintImage should remain unchanged.
   // If the external inputs for deciding the decode policy for an image change,
   // they should be accompanied with an invalidation during paint.
   image_id_to_decode_.clear();

   if (can_clear_decode_policy_tracking) {
     image_async_decode_state_.clear();
   } else {
     // If we can't clear the decode policy, we need to make sure we still
     // re-decode and checker images that were pending invalidation.
     for (auto image_id : images_pending_invalidation_) {
       auto it = image_async_decode_state_.find(image_id);
       DCHECK(it != image_async_decode_state_.end());
       DCHECK_EQ(it->second.policy, DecodePolicy::SYNC);
       it->second.policy = DecodePolicy::ASYNC;
     }
   }
   images_pending_invalidation_.clear();
 }

 void CheckerImageTracker::DisallowCheckeringForImage(const PaintImage& image) {
   image_async_decode_state_.insert(
       std::make_pair(image.stable_id(), DecodeState()));
 }

 void CheckerImageTracker::DidFinishImageDecode(
     PaintImage::Id image_id,
     ImageController::ImageDecodeRequestId request_id,
     ImageController::ImageDecodeResult result) {
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
                "CheckerImageTracker::DidFinishImageDecode");
   TRACE_EVENT_ASYNC_END0("cc", "CheckerImageTracker::DeferImageDecode",
                          image_id);

   DCHECK_NE(ImageController::ImageDecodeResult::DECODE_NOT_REQUIRED, result);
   DCHECK_EQ(outstanding_image_decode_.value().stable_id(), image_id);
   outstanding_image_decode_.reset();

   // The async decode state may have been cleared if the tracker was cleared
   // before this decode could be finished.
   auto it = image_async_decode_state_.find(image_id);
   if (it == image_async_decode_state_.end()) {
     DCHECK_EQ(image_id_to_decode_.count(image_id), 0u);
     return;
   }

   // We might have flipped this to sync while updating the hints. That function
   // would have also requested an invalidation, so we can just schedule the next
   // decode here.
   if (it->second.policy == DecodePolicy::SYNC) {
     DCHECK(decoding_mode_map_.find(image_id) != decoding_mode_map_.end());
     DCHECK_EQ(decoding_mode_map_[image_id], PaintImage::DecodingMode::kSync);

     ScheduleNextImageDecode();
     return;
   }

   it->second.policy = DecodePolicy::SYNC;
   images_pending_invalidation_.insert(image_id);
   ScheduleNextImageDecode();
   client_->NeedsInvalidationForCheckerImagedTiles();
 }

 bool CheckerImageTracker::ShouldCheckerImage(const DrawImage& draw_image,
                                              WhichTree tree) {
   const PaintImage& image = draw_image.paint_image();
   PaintImage::Id image_id = image.stable_id();
   TRACE_EVENT1("cc.debug", "CheckerImageTracker::ShouldCheckerImage",
                "image_id", image_id);

   // Checkering of all images is disabled.
   if (!enable_checker_imaging_)
     return false;

   // If the image was invalidated on the current sync tree and the tile is
   // for the active tree, continue checkering it on the active tree to ensure
   // the image update is atomic for the frame.
   if (invalidated_images_on_current_sync_tree_.count(image_id) != 0 &&
       tree == WhichTree::ACTIVE_TREE) {
     return true;
   }

   // If the image is pending invalidation, continue checkering it. All tiles
   // for these images will be invalidated on the next pending tree.
   if (images_pending_invalidation_.find(image_id) !=
       images_pending_invalidation_.end()) {
     return true;
   }

   auto decoding_mode_it = decoding_mode_map_.find(image_id);
   PaintImage::DecodingMode decoding_mode_hint =
       decoding_mode_it == decoding_mode_map_.end()
           ? PaintImage::DecodingMode::kUnspecified
           : decoding_mode_it->second;

   // We only checker images if the developer specifies async decoding mode.
   if (decoding_mode_hint != PaintImage::DecodingMode::kAsync)
     return false;

   auto insert_result = image_async_decode_state_.insert(
       std::pair<PaintImage::Id, DecodeState>(image_id, DecodeState()));
   auto it = insert_result.first;
   if (insert_result.second) {
     CheckerImagingDecision decision = CheckerImagingDecision::kCanChecker;
     // If the mode is sync, then don't checker this image.
     // TODO(vmpstr): Figure out if we should do something different in other
     // cases.
     if (decoding_mode_hint == PaintImage::DecodingMode::kSync)
       decision = CheckerImagingDecision::kVetoedSyncRequested;

     // The following conditions must be true for an image to be checkerable:
     //
     // 1) Complete: The data for the image should have been completely loaded.
     //
     // 2) Static: Animated images/video frames can not be checkered.
     //
     // 3) Size constraints: Small images for which the decode is expected to
     // be fast and large images which would breach the image cache budget and
     // go through the at-raster decode path are not checkered.
     //
     // 4) Multipart images: Multipart images can be used to display mjpg video
     // frames, checkering which would cause each video frame to flash and
     // therefore should not be checkered.
     //
     // Note that we only need to do this check if we didn't veto above in this
     // block.
     if (decision == CheckerImagingDecision::kCanChecker) {
       decision = GetCheckerImagingDecision(
           image, draw_image.src_rect(), min_image_bytes_to_checker_,
           image_controller_->image_cache_max_limit_bytes());
     }

     if (decision == CheckerImagingDecision::kCanChecker && force_disabled_) {
       // Get the decision for all the veto reasons first, so we can UMA the
       // images that were not checkered only because checker-imaging was force
       // disabled.
       decision = CheckerImagingDecision::kVetoedForceDisable;
     }

     it->second.policy = decision == CheckerImagingDecision::kCanChecker
                             ? DecodePolicy::ASYNC
                             : DecodePolicy::SYNC;

     UMA_HISTOGRAM_ENUMERATION(
         "Compositing.Renderer.CheckerImagingDecision", decision,
         CheckerImagingDecision::kCheckerImagingDecisionCount);

     TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
                  "CheckerImageTracker::CheckerImagingDecision", "image_params",
                  ToString(image_id, decision));
   }

   // Update the decode state from the latest image we have seen. Note that it
   // is not necessary to perform this in the early out cases above since in
   // each of those cases the image has already been decoded.
   UpdateDecodeState(draw_image, image_id, &it->second);

   return it->second.policy == DecodePolicy::ASYNC;
 }

 void CheckerImageTracker::UpdateDecodeState(const DrawImage& draw_image,
                                             PaintImage::Id paint_image_id,
                                             DecodeState* decode_state) {
   // If the policy is not async then either we decoded this image already or
   // we decided not to ever checker it.
   if (decode_state->policy != DecodePolicy::ASYNC)
     return;

   // If the decode is already in flight, then we will have to live with what we
   // have now.
   if (outstanding_image_decode_.has_value() &&
       outstanding_image_decode_.value().stable_id() == paint_image_id) {
     return;
   }

   // Choose the max scale and filter quality. This keeps the memory usage to the
   // minimum possible while still increasing the possibility of getting a cache
   // hit.
   decode_state->scale = SkSize::Make(
       std::max(decode_state->scale.fWidth, draw_image.scale().fWidth),
       std::max(decode_state->scale.fHeight, draw_image.scale().fHeight));
   decode_state->filter_quality =
       std::max(decode_state->filter_quality, draw_image.filter_quality());
   decode_state->frame_index = draw_image.frame_index();
 }

 void CheckerImageTracker::ScheduleNextImageDecode() {
   TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
                "CheckerImageTracker::ScheduleNextImageDecode");
   // We can have only one outstanding decode pending completion with the decode
   // service. We'll come back here when it is completed.
   if (outstanding_image_decode_.has_value())
     return;

   if (image_decode_queue_.empty())
     return;

   // If scheduling decodes for this priority is not allowed right now, don't
   // schedule them. We will come back here when the allowed priority changes.
   if (image_decode_queue_.front().type > decode_priority_allowed_)
     return;

   DrawImage draw_image;
   while (!image_decode_queue_.empty()) {
     auto candidate = std::move(image_decode_queue_.front().paint_image);
     image_decode_queue_.erase(image_decode_queue_.begin());

     // Once an image has been decoded, it can still be present in the decode
     // queue (duplicate entries), or while an image is still being skipped on
     // the active tree. Check if the image is still ASYNC to see if a decode is
     // needed.
     PaintImage::Id image_id = candidate.stable_id();
     auto it = image_async_decode_state_.find(image_id);
     DCHECK(it != image_async_decode_state_.end());
     if (it->second.policy != DecodePolicy::ASYNC)
       continue;

     draw_image = DrawImage(
         candidate, SkIRect::MakeWH(candidate.width(), candidate.height()),
         it->second.filter_quality,
         SkMatrix::MakeScale(it->second.scale.width(),
                             it->second.scale.height()),
         it->second.frame_index);
     outstanding_image_decode_.emplace(candidate);
     break;
   }

   // We either found an image to decode or we reached the end of the queue. If
   // we couldn't find an image, we're done.
   if (!outstanding_image_decode_.has_value()) {
     DCHECK(image_decode_queue_.empty());
     return;
   }

   PaintImage::Id image_id = outstanding_image_decode_.value().stable_id();
   DCHECK_EQ(image_id_to_decode_.count(image_id), 0u);
   TRACE_EVENT_ASYNC_BEGIN0("cc", "CheckerImageTracker::DeferImageDecode",
                            image_id);
   ImageController::ImageDecodeRequestId request_id =
       image_controller_->QueueImageDecode(
           draw_image, base::Bind(&CheckerImageTracker::DidFinishImageDecode,
                                  weak_factory_.GetWeakPtr(), image_id));

   image_id_to_decode_.emplace(image_id, std::make_unique<ScopedDecodeHolder>(
                                             image_controller_, request_id));
 }

 void CheckerImageTracker::UpdateImageDecodingHints(
     base::flat_map<PaintImage::Id, PaintImage::DecodingMode>
         decoding_mode_map) {
   // Merge the |decoding_mode_map| with our member map, keeping the more
   // conservative values.
   // TODO(vmpstr): Figure out if and how do we clear this value to ensure that
   // if we no longer have any kSync images, for example, then we can loosen the
   // requirement on the decoding mode for that image id.
   for (auto pair : decoding_mode_map) {
     PaintImage::Id id = pair.first;
     PaintImage::DecodingMode decoding_mode = pair.second;

     // In case we already have this image as async, it implies that we are
     // currently displaying this content as checkered. We can flip the state to
     // sync here and add the image to be invalidated. The invalidation should
     // happen shortly after, since this function should be called in a commit.
     auto state_it = image_async_decode_state_.find(id);
     if (state_it != image_async_decode_state_.end()) {
       auto& state = state_it->second;
       if (state.policy == DecodePolicy::ASYNC &&
           decoding_mode == PaintImage::DecodingMode::kSync) {
         state.policy = DecodePolicy::SYNC;
         images_pending_invalidation_.insert(id);
       }
     }

     // Update the decoding hints map.
     auto decoding_mode_it = decoding_mode_map_.find(id);
     if (decoding_mode_it == decoding_mode_map_.end()) {
       decoding_mode_map_[id] = decoding_mode;
     } else {
       decoding_mode_it->second =
           PaintImage::GetConservative(decoding_mode_it->second, decoding_mode);
     }
   }
 }

 }  // namespace cc
	// 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.

	#include "cc/tiles/checker_image_tracker.h"

	#include "base/bind.h"
	#include "base/metrics/histogram_macros.h"
	#include "base/stl_util.h"
	#include "base/trace_event/trace_event.h"

	namespace cc {
	namespace {
	// The enum for recording checker-imaging decision UMA metric. Keep this
	// consistent with the ordering in CheckerImagingDecision in enums.xml.
	// Note that this enum is used to back a UMA histogram so should be treated as
	// append only.
	enum class CheckerImagingDecision {
	kCanChecker = 0,

	// Animation State vetoes.
	kVetoedAnimatedImage = 1,
	kVetoedVideoFrame = 2,
	// TODO(vmpstr): 3 used to be kVetoedAnimationUnknown, remove it somehow?
	kVetoedMultipartImage = 4,

	// Load state vetoes.
	kVetoedPartiallyLoadedImage = 5,
	// TODO(vmpstr): 6 used to be kVetoedLoadStateUnknown, remove it somehow?

	// Size associated vetoes.
	kVetoedSmallerThanCheckeringSize = 7,
	kVetoedLargerThanCacheSize = 8,

	// Vetoed because checkering of images has been disabled.
	kVetoedForceDisable = 9,

	// 10 used to be kVetoedNotRequiredForActivation.

	// Sync was requested by the embedder.
	kVetoedSyncRequested = 11,

	kCheckerImagingDecisionCount
	};

	std::string ToString(PaintImage::Id paint_image_id,
	CheckerImagingDecision decision) {
	std::ostringstream str;
	str << "paint_image_id[" << paint_image_id << "] decision["
	<< static_cast<int>(decision) << "]";
	return str.str();
	}

	CheckerImagingDecision GetAnimationDecision(const PaintImage& image) {
	if (image.is_multipart())
	return CheckerImagingDecision::kVetoedMultipartImage;

	switch (image.animation_type()) {
	case PaintImage::AnimationType::ANIMATED:
	return CheckerImagingDecision::kVetoedAnimatedImage;
	case PaintImage::AnimationType::VIDEO:
	return CheckerImagingDecision::kVetoedVideoFrame;
	case PaintImage::AnimationType::STATIC:
	return CheckerImagingDecision::kCanChecker;
	}

	NOTREACHED();
	return CheckerImagingDecision::kCanChecker;
	}

	CheckerImagingDecision GetLoadDecision(const PaintImage& image) {
	switch (image.completion_state()) {
	case PaintImage::CompletionState::DONE:
	return CheckerImagingDecision::kCanChecker;
	case PaintImage::CompletionState::PARTIALLY_DONE:
	return CheckerImagingDecision::kVetoedPartiallyLoadedImage;
	}

	NOTREACHED();
	return CheckerImagingDecision::kCanChecker;
	}

	CheckerImagingDecision GetSizeDecision(const SkIRect& src_rect,
	size_t min_bytes,
	size_t max_bytes) {
	// Ideally we would use the original image rect here to estimate the decode
	// duration for this image. But in the case of sprites/atlases, where small
	// subsets of this image are used across multiple tiles, re-invalidating for
	// replacing these images can incur heavy raster cost. So we use the src_rect
	// here instead.
	// TODO(khushalsagar): May be we should look at the invalidation rect for an
	// image here to detect these cases instead?
	base::CheckedNumeric<size_t> checked_size = 4;
	checked_size *= src_rect.width();
	checked_size *= src_rect.height();
	size_t size = checked_size.ValueOrDefault(std::numeric_limits<size_t>::max());

	if (size < min_bytes)
	return CheckerImagingDecision::kVetoedSmallerThanCheckeringSize;
	else if (size > max_bytes)
	return CheckerImagingDecision::kVetoedLargerThanCacheSize;
	else
	return CheckerImagingDecision::kCanChecker;
	}

	CheckerImagingDecision GetCheckerImagingDecision(const PaintImage& image,
	const SkIRect& src_rect,
	size_t min_bytes,
	size_t max_bytes) {
	CheckerImagingDecision decision = GetAnimationDecision(image);
	if (decision != CheckerImagingDecision::kCanChecker)
	return decision;

	decision = GetLoadDecision(image);
	if (decision != CheckerImagingDecision::kCanChecker)
	return decision;

	return GetSizeDecision(src_rect, min_bytes, max_bytes);
	}

	} // namespace

	// static
	const int CheckerImageTracker::kNoDecodeAllowedPriority = -1;

	CheckerImageTracker::ImageDecodeRequest::ImageDecodeRequest(
	PaintImage paint_image,
	DecodeType type)
	: paint_image(std::move(paint_image)), type(type) {}

	CheckerImageTracker::CheckerImageTracker(ImageController* image_controller,
	CheckerImageTrackerClient* client,
	bool enable_checker_imaging,
	size_t min_image_bytes_to_checker)
	: image_controller_(image_controller),
	client_(client),
	enable_checker_imaging_(enable_checker_imaging),
	min_image_bytes_to_checker_(min_image_bytes_to_checker),
	weak_factory_(this) {}

	CheckerImageTracker::~CheckerImageTracker() = default;

	void CheckerImageTracker::SetNoDecodesAllowed() {
	decode_priority_allowed_ = kNoDecodeAllowedPriority;
	}

	void CheckerImageTracker::SetMaxDecodePriorityAllowed(DecodeType decode_type) {
	DCHECK_GT(decode_type, kNoDecodeAllowedPriority);
	DCHECK_GE(decode_type, decode_priority_allowed_);
	DCHECK_LE(decode_type, DecodeType::kLast);

	if (decode_priority_allowed_ == decode_type)
	return;
	decode_priority_allowed_ = decode_type;

	// This will start the next decode if applicable.
	ScheduleNextImageDecode();
	}

	void CheckerImageTracker::ScheduleImageDecodeQueue(
	ImageDecodeQueue image_decode_queue) {
	TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
	"CheckerImageTracker::ScheduleImageDecodeQueue");
	#if DCHECK_IS_ON()
	// The decodes in the queue should be prioritized correctly.
	DecodeType type = DecodeType::kRaster;
	for (const auto& image_request : image_decode_queue) {
	DCHECK_GE(image_request.type, type);
	type = image_request.type;
	}
	#endif

	image_decode_queue_ = std::move(image_decode_queue);
	ScheduleNextImageDecode();
	}

	const PaintImageIdFlatSet&
	CheckerImageTracker::TakeImagesToInvalidateOnSyncTree() {
	TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
	"CheckerImageTracker::TakeImagesToInvalidateOnSyncTree");
	DCHECK_EQ(invalidated_images_on_current_sync_tree_.size(), 0u)
	<< "Sync tree can not be invalidated more than once";

	invalidated_images_on_current_sync_tree_.swap(images_pending_invalidation_);
	images_pending_invalidation_.clear();
	return invalidated_images_on_current_sync_tree_;
	}

	void CheckerImageTracker::DidActivateSyncTree() {
	TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
	"CheckerImageTracker::DidActivateSyncTree");
	for (auto image_id : invalidated_images_on_current_sync_tree_)
	image_id_to_decode_.erase(image_id);
	invalidated_images_on_current_sync_tree_.clear();
	}

	void CheckerImageTracker::ClearTracker(bool can_clear_decode_policy_tracking) {
	// Unlock all images and tracking for images pending invalidation. The
	// \|images_invalidated_on_current_sync_tree_\| will be cleared when the sync
	// tree is activated.
	//
	// Note that we assume that any images with DecodePolicy::ASYNC, which may be
	// checkered, are safe to stop tracking here and will either be re-checkered
	// and invalidated when the decode completes or be invalidated externally.
	// This is because the policy decision for checkering an image is based on
	// inputs received from a PaintImage in the DisplayItemList. The policy chosen
	// for a PaintImage should remain unchanged.
	// If the external inputs for deciding the decode policy for an image change,
	// they should be accompanied with an invalidation during paint.
	image_id_to_decode_.clear();

	if (can_clear_decode_policy_tracking) {
	image_async_decode_state_.clear();
	} else {
	// If we can't clear the decode policy, we need to make sure we still
	// re-decode and checker images that were pending invalidation.
	for (auto image_id : images_pending_invalidation_) {
	auto it = image_async_decode_state_.find(image_id);
	DCHECK(it != image_async_decode_state_.end());
	DCHECK_EQ(it->second.policy, DecodePolicy::SYNC);
	it->second.policy = DecodePolicy::ASYNC;
	}
	}
	images_pending_invalidation_.clear();
	}

	void CheckerImageTracker::DisallowCheckeringForImage(const PaintImage& image) {
	image_async_decode_state_.insert(
	std::make_pair(image.stable_id(), DecodeState()));
	}

	void CheckerImageTracker::DidFinishImageDecode(
	PaintImage::Id image_id,
	ImageController::ImageDecodeRequestId request_id,
	ImageController::ImageDecodeResult result) {
	TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
	"CheckerImageTracker::DidFinishImageDecode");
	TRACE_EVENT_ASYNC_END0("cc", "CheckerImageTracker::DeferImageDecode",
	image_id);

	DCHECK_NE(ImageController::ImageDecodeResult::DECODE_NOT_REQUIRED, result);
	DCHECK_EQ(outstanding_image_decode_.value().stable_id(), image_id);
	outstanding_image_decode_.reset();

	// The async decode state may have been cleared if the tracker was cleared
	// before this decode could be finished.
	auto it = image_async_decode_state_.find(image_id);
	if (it == image_async_decode_state_.end()) {
	DCHECK_EQ(image_id_to_decode_.count(image_id), 0u);
	return;
	}

	// We might have flipped this to sync while updating the hints. That function
	// would have also requested an invalidation, so we can just schedule the next
	// decode here.
	if (it->second.policy == DecodePolicy::SYNC) {
	DCHECK(decoding_mode_map_.find(image_id) != decoding_mode_map_.end());
	DCHECK_EQ(decoding_mode_map_[image_id], PaintImage::DecodingMode::kSync);

	ScheduleNextImageDecode();
	return;
	}

	it->second.policy = DecodePolicy::SYNC;
	images_pending_invalidation_.insert(image_id);
	ScheduleNextImageDecode();
	client_->NeedsInvalidationForCheckerImagedTiles();
	}

	bool CheckerImageTracker::ShouldCheckerImage(const DrawImage& draw_image,
	WhichTree tree) {
	const PaintImage& image = draw_image.paint_image();
	PaintImage::Id image_id = image.stable_id();
	TRACE_EVENT1("cc.debug", "CheckerImageTracker::ShouldCheckerImage",
	"image_id", image_id);

	// Checkering of all images is disabled.
	if (!enable_checker_imaging_)
	return false;

	// If the image was invalidated on the current sync tree and the tile is
	// for the active tree, continue checkering it on the active tree to ensure
	// the image update is atomic for the frame.
	if (invalidated_images_on_current_sync_tree_.count(image_id) != 0 &&
	tree == WhichTree::ACTIVE_TREE) {
	return true;
	}

	// If the image is pending invalidation, continue checkering it. All tiles
	// for these images will be invalidated on the next pending tree.
	if (images_pending_invalidation_.find(image_id) !=
	images_pending_invalidation_.end()) {
	return true;
	}

	auto decoding_mode_it = decoding_mode_map_.find(image_id);
	PaintImage::DecodingMode decoding_mode_hint =
	decoding_mode_it == decoding_mode_map_.end()
	? PaintImage::DecodingMode::kUnspecified
	: decoding_mode_it->second;

	// We only checker images if the developer specifies async decoding mode.
	if (decoding_mode_hint != PaintImage::DecodingMode::kAsync)
	return false;

	auto insert_result = image_async_decode_state_.insert(
	std::pair<PaintImage::Id, DecodeState>(image_id, DecodeState()));
	auto it = insert_result.first;
	if (insert_result.second) {
	CheckerImagingDecision decision = CheckerImagingDecision::kCanChecker;
	// If the mode is sync, then don't checker this image.
	// TODO(vmpstr): Figure out if we should do something different in other
	// cases.
	if (decoding_mode_hint == PaintImage::DecodingMode::kSync)
	decision = CheckerImagingDecision::kVetoedSyncRequested;

	// The following conditions must be true for an image to be checkerable:
	//
	// 1) Complete: The data for the image should have been completely loaded.
	//
	// 2) Static: Animated images/video frames can not be checkered.
	//
	// 3) Size constraints: Small images for which the decode is expected to
	// be fast and large images which would breach the image cache budget and
	// go through the at-raster decode path are not checkered.
	//
	// 4) Multipart images: Multipart images can be used to display mjpg video
	// frames, checkering which would cause each video frame to flash and
	// therefore should not be checkered.
	//
	// Note that we only need to do this check if we didn't veto above in this
	// block.
	if (decision == CheckerImagingDecision::kCanChecker) {
	decision = GetCheckerImagingDecision(
	image, draw_image.src_rect(), min_image_bytes_to_checker_,
	image_controller_->image_cache_max_limit_bytes());
	}

	if (decision == CheckerImagingDecision::kCanChecker && force_disabled_) {
	// Get the decision for all the veto reasons first, so we can UMA the
	// images that were not checkered only because checker-imaging was force
	// disabled.
	decision = CheckerImagingDecision::kVetoedForceDisable;
	}

	it->second.policy = decision == CheckerImagingDecision::kCanChecker
	? DecodePolicy::ASYNC
	: DecodePolicy::SYNC;

	UMA_HISTOGRAM_ENUMERATION(
	"Compositing.Renderer.CheckerImagingDecision", decision,
	CheckerImagingDecision::kCheckerImagingDecisionCount);

	TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
	"CheckerImageTracker::CheckerImagingDecision", "image_params",
	ToString(image_id, decision));
	}

	// Update the decode state from the latest image we have seen. Note that it
	// is not necessary to perform this in the early out cases above since in
	// each of those cases the image has already been decoded.
	UpdateDecodeState(draw_image, image_id, &it->second);

	return it->second.policy == DecodePolicy::ASYNC;
	}

	void CheckerImageTracker::UpdateDecodeState(const DrawImage& draw_image,
	PaintImage::Id paint_image_id,
	DecodeState* decode_state) {
	// If the policy is not async then either we decoded this image already or
	// we decided not to ever checker it.
	if (decode_state->policy != DecodePolicy::ASYNC)
	return;

	// If the decode is already in flight, then we will have to live with what we
	// have now.
	if (outstanding_image_decode_.has_value() &&
	outstanding_image_decode_.value().stable_id() == paint_image_id) {
	return;
	}

	// Choose the max scale and filter quality. This keeps the memory usage to the
	// minimum possible while still increasing the possibility of getting a cache
	// hit.
	decode_state->scale = SkSize::Make(
	std::max(decode_state->scale.fWidth, draw_image.scale().fWidth),
	std::max(decode_state->scale.fHeight, draw_image.scale().fHeight));
	decode_state->filter_quality =
	std::max(decode_state->filter_quality, draw_image.filter_quality());
	decode_state->frame_index = draw_image.frame_index();
	}

	void CheckerImageTracker::ScheduleNextImageDecode() {
	TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
	"CheckerImageTracker::ScheduleNextImageDecode");
	// We can have only one outstanding decode pending completion with the decode
	// service. We'll come back here when it is completed.
	if (outstanding_image_decode_.has_value())
	return;

	if (image_decode_queue_.empty())
	return;

	// If scheduling decodes for this priority is not allowed right now, don't
	// schedule them. We will come back here when the allowed priority changes.
	if (image_decode_queue_.front().type > decode_priority_allowed_)
	return;

	DrawImage draw_image;
	while (!image_decode_queue_.empty()) {
	auto candidate = std::move(image_decode_queue_.front().paint_image);
	image_decode_queue_.erase(image_decode_queue_.begin());

	// Once an image has been decoded, it can still be present in the decode
	// queue (duplicate entries), or while an image is still being skipped on
	// the active tree. Check if the image is still ASYNC to see if a decode is
	// needed.
	PaintImage::Id image_id = candidate.stable_id();
	auto it = image_async_decode_state_.find(image_id);
	DCHECK(it != image_async_decode_state_.end());
	if (it->second.policy != DecodePolicy::ASYNC)
	continue;

	draw_image = DrawImage(
	candidate, SkIRect::MakeWH(candidate.width(), candidate.height()),
	it->second.filter_quality,
	SkMatrix::MakeScale(it->second.scale.width(),
	it->second.scale.height()),
	it->second.frame_index);
	outstanding_image_decode_.emplace(candidate);
	break;
	}

	// We either found an image to decode or we reached the end of the queue. If
	// we couldn't find an image, we're done.
	if (!outstanding_image_decode_.has_value()) {
	DCHECK(image_decode_queue_.empty());
	return;
	}

	PaintImage::Id image_id = outstanding_image_decode_.value().stable_id();
	DCHECK_EQ(image_id_to_decode_.count(image_id), 0u);
	TRACE_EVENT_ASYNC_BEGIN0("cc", "CheckerImageTracker::DeferImageDecode",
	image_id);
	ImageController::ImageDecodeRequestId request_id =
	image_controller_->QueueImageDecode(
	draw_image, base::Bind(&CheckerImageTracker::DidFinishImageDecode,
	weak_factory_.GetWeakPtr(), image_id));

	image_id_to_decode_.emplace(image_id, std::make_unique<ScopedDecodeHolder>(
	image_controller_, request_id));
	}

	void CheckerImageTracker::UpdateImageDecodingHints(
	base::flat_map<PaintImage::Id, PaintImage::DecodingMode>
	decoding_mode_map) {
	// Merge the \|decoding_mode_map\| with our member map, keeping the more
	// conservative values.
	// TODO(vmpstr): Figure out if and how do we clear this value to ensure that
	// if we no longer have any kSync images, for example, then we can loosen the
	// requirement on the decoding mode for that image id.
	for (auto pair : decoding_mode_map) {
	PaintImage::Id id = pair.first;
	PaintImage::DecodingMode decoding_mode = pair.second;

	// In case we already have this image as async, it implies that we are
	// currently displaying this content as checkered. We can flip the state to
	// sync here and add the image to be invalidated. The invalidation should
	// happen shortly after, since this function should be called in a commit.
	auto state_it = image_async_decode_state_.find(id);
	if (state_it != image_async_decode_state_.end()) {
	auto& state = state_it->second;
	if (state.policy == DecodePolicy::ASYNC &&
	decoding_mode == PaintImage::DecodingMode::kSync) {
	state.policy = DecodePolicy::SYNC;
	images_pending_invalidation_.insert(id);
	}
	}

	// Update the decoding hints map.
	auto decoding_mode_it = decoding_mode_map_.find(id);
	if (decoding_mode_it == decoding_mode_map_.end()) {
	decoding_mode_map_[id] = decoding_mode;
	} else {
	decoding_mode_it->second =
	PaintImage::GetConservative(decoding_mode_it->second, decoding_mode);
	}
	}
	}

	} // namespace cc