author Kartikaya Gupta <>
Mon, 16 Apr 2018 17:39:26 -0400
changeset 467791 7ccbfd4a28d79aed59887b322af44ca0b80d2390
parent 467790 61724e1bb2ad7d0642d4d4cd7c05a396f44b7591
child 468206 fbfbfe496fcb39556a00f9209116b8374e79bcb7
permissions -rw-r--r--
Bug 1451469 - Complete hooking up of the sampler thread. r=botond,nical This makes the APZ sampler thread be the render backend thread whenever webrender is being used (not just when async scene building is enabled). MozReview-Commit-ID: L9lmopd3pe7

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at */

#ifndef mozilla_layers_APZSampler_h
#define mozilla_layers_APZSampler_h

#include <unordered_map>

#include "base/platform_thread.h" // for PlatformThreadId
#include "mozilla/layers/AsyncCompositionManager.h" // for AsyncTransform
#include "mozilla/StaticMutex.h"
#include "nsTArray.h"
#include "Units.h"

namespace mozilla {

class TimeStamp;

namespace wr {
struct Transaction;
class TransactionWrapper;
struct WrTransformProperty;
struct WrWindowId;
} // namespace wr

namespace layers {

class APZCTreeManager;
class LayerMetricsWrapper;
struct ScrollbarData;

 * This interface exposes APZ methods related to "sampling" (i.e. reading the
 * async transforms produced by APZ). These methods should all be called on
 * the sampler thread.
class APZSampler {

  explicit APZSampler(const RefPtr<APZCTreeManager>& aApz);

  void SetWebRenderWindowId(const wr::WindowId& aWindowId);

   * This function is invoked from rust on the render backend thread when it
   * is created. It effectively tells the APZSampler "the current thread is
   * the sampler thread for this window id" and allows APZSampler to remember
   * which thread it is.
  static void SetSamplerThread(const wr::WrWindowId& aWindowId);
  static void SampleForWebRender(const wr::WrWindowId& aWindowId,
                                 wr::Transaction* aTxn);

  void SetSampleTime(const TimeStamp& aSampleTime);
  void SampleForWebRender(wr::TransactionWrapper& aTxn);

  bool SampleAnimations(const LayerMetricsWrapper& aLayer,
                        const TimeStamp& aSampleTime);

   * Compute the updated shadow transform for a scroll thumb layer that
   * reflects async scrolling of the associated scroll frame.
   * Refer to APZCTreeManager::ComputeTransformForScrollThumb for the
   * description of parameters. The only difference is that this function takes
   * |aContent| instead of |aApzc| and |aMetrics|; aContent is the
   * LayerMetricsWrapper corresponding to the scroll frame that is scrolled by
   * the scroll thumb, and so the APZC and metrics can be obtained from
   * |aContent|.
  LayerToParentLayerMatrix4x4 ComputeTransformForScrollThumb(
      const LayerToParentLayerMatrix4x4& aCurrentTransform,
      const LayerMetricsWrapper& aContent,
      const ScrollbarData& aThumbData,
      bool aScrollbarIsDescendant,
      AsyncTransformComponentMatrix* aOutClipTransform);

  ParentLayerPoint GetCurrentAsyncScrollOffset(const LayerMetricsWrapper& aLayer);
  AsyncTransform GetCurrentAsyncTransform(const LayerMetricsWrapper& aLayer);
  AsyncTransformComponentMatrix GetOverscrollTransform(const LayerMetricsWrapper& aLayer);
  AsyncTransformComponentMatrix GetCurrentAsyncTransformWithOverscroll(const LayerMetricsWrapper& aLayer);

  void MarkAsyncTransformAppliedToContent(const LayerMetricsWrapper& aLayer);
  bool HasUnusedAsyncTransform(const LayerMetricsWrapper& aLayer);

   * This can be used to assert that the current thread is the
   * sampler thread (which samples the async transform).
   * This does nothing if thread assertions are disabled.
  void AssertOnSamplerThread() const;

   * Returns true if currently on the APZSampler's "sampler thread".
  bool IsSamplerThread() const;

  virtual ~APZSampler();

  bool UsingWebRenderSamplerThread() const;
  static already_AddRefed<APZSampler> GetSampler(const wr::WrWindowId& aWindowId);

  RefPtr<APZCTreeManager> mApz;

  // Used to manage the mapping from a WR window id to APZSampler. These are only
  // used if WebRender is enabled. Both sWindowIdMap and mWindowId should only
  // be used while holding the sWindowIdLock.
  static StaticMutex sWindowIdLock;
  static std::unordered_map<uint64_t, APZSampler*> sWindowIdMap;
  Maybe<wr::WrWindowId> mWindowId;

  // If WebRender is enabled, this holds the thread id of the render backend
  // thread (which is the sampler thread) for the compositor associated with
  // this APZSampler instance.
  // This is written to once during init and never cleared, and so reading it
  // from multiple threads during normal operation (after initialization)
  // without locking should be fine.
  Maybe<PlatformThreadId> mSamplerThreadId;
#ifdef DEBUG
  // This flag is used to ensure that we don't ever try to do sampler-thread
  // stuff before the updater thread has been properly initialized.
  mutable bool mSamplerThreadQueried;

  Mutex mSampleTimeLock;
  // Can only be accessed or modified while holding mSampleTimeLock.
  TimeStamp mSampleTime;

} // namespace layers
} // namespace mozilla

#endif // mozilla_layers_APZSampler_h