gecko-dev/gfx/thebes/SoftwareVsyncSource.cpp

/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * 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 http://mozilla.org/MPL/2.0/.
 */

#include "SoftwareVsyncSource.h"
#include "base/task.h"
#include "gfxPlatform.h"
#include "nsThreadUtils.h"

namespace mozilla::gfx {

SoftwareVsyncSource::SoftwareVsyncSource(const TimeDuration& aInitialVsyncRate)
    : mVsyncEnabled(false),
      mVsyncRate(TimeDuration{aInitialVsyncRate},
                 "SoftwareVsyncSource::mVsyncRate") {
  MOZ_ASSERT(NS_IsMainThread());
  mVsyncThread = new base::Thread("SoftwareVsyncThread");
  MOZ_RELEASE_ASSERT(mVsyncThread->Start(),
                     "GFX: Could not start software vsync thread");
}

SoftwareVsyncSource::~SoftwareVsyncSource() {
  MOZ_ASSERT(NS_IsMainThread());
  if (mVsyncThread) {
    mVsyncThread->Stop();
    delete mVsyncThread;
  }
};

void SoftwareVsyncSource::EnableVsync() {
  MOZ_ASSERT(mVsyncThread->IsRunning());
  if (NS_IsMainThread()) {
    if (mVsyncEnabled) {
      return;
    }
    mVsyncEnabled = true;

    mVsyncThread->message_loop()->PostTask(
        NewRunnableMethod("SoftwareVsyncSource::EnableVsync", this,
                          &SoftwareVsyncSource::EnableVsync));
    return;
  }

  MOZ_ASSERT(IsInSoftwareVsyncThread());
  TimeStamp vsyncTime = TimeStamp::Now();
  TimeStamp outputTime = vsyncTime + GetVsyncRate();
  NotifyVsync(vsyncTime, outputTime);
}

void SoftwareVsyncSource::DisableVsync() {
  MOZ_ASSERT(mVsyncThread->IsRunning());
  if (NS_IsMainThread()) {
    if (!mVsyncEnabled) {
      return;
    }
    mVsyncEnabled = false;

    mVsyncThread->message_loop()->PostTask(
        NewRunnableMethod("SoftwareVsyncSource::DisableVsync", this,
                          &SoftwareVsyncSource::DisableVsync));
    return;
  }

  MOZ_ASSERT(IsInSoftwareVsyncThread());
  if (mCurrentVsyncTask) {
    mCurrentVsyncTask->Cancel();
    mCurrentVsyncTask = nullptr;
  }
}

bool SoftwareVsyncSource::IsVsyncEnabled() {
  MOZ_ASSERT(NS_IsMainThread());
  return mVsyncEnabled;
}

bool SoftwareVsyncSource::IsInSoftwareVsyncThread() {
  return mVsyncThread->thread_id() == PlatformThread::CurrentId();
}

void SoftwareVsyncSource::NotifyVsync(const TimeStamp& aVsyncTimestamp,
                                      const TimeStamp& aOutputTimestamp) {
  MOZ_ASSERT(IsInSoftwareVsyncThread());

  TimeStamp displayVsyncTime = aVsyncTimestamp;
  TimeStamp now = TimeStamp::Now();
  // Posted tasks can only have integer millisecond delays
  // whereas TimeDurations can have floating point delays.
  // Thus the vsync timestamp can be in the future, which large parts
  // of the system can't handle, including animations. Force the timestamp to be
  // now.
  if (aVsyncTimestamp > now) {
    displayVsyncTime = now;
  }

  VsyncSource::NotifyVsync(displayVsyncTime, aOutputTimestamp);

  // Prevent skew by still scheduling based on the original
  // vsync timestamp
  ScheduleNextVsync(aVsyncTimestamp);
}

TimeDuration SoftwareVsyncSource::GetVsyncRate() {
  auto rate = mVsyncRate.Lock();
  return *rate;
}

void SoftwareVsyncSource::SetVsyncRate(const TimeDuration& aNewRate) {
  auto rate = mVsyncRate.Lock();
  *rate = aNewRate;
}

void SoftwareVsyncSource::ScheduleNextVsync(TimeStamp aVsyncTimestamp) {
  MOZ_ASSERT(IsInSoftwareVsyncThread());
  TimeDuration vsyncRate = GetVsyncRate();
  TimeStamp nextVsync = aVsyncTimestamp + vsyncRate;
  TimeDuration delay = nextVsync - TimeStamp::Now();
  if (delay.ToMilliseconds() < 0) {
    delay = TimeDuration::FromMilliseconds(0);
    nextVsync = TimeStamp::Now();
  }

  TimeStamp outputTime = nextVsync + vsyncRate;

  mCurrentVsyncTask = NewCancelableRunnableMethod<TimeStamp, TimeStamp>(
      "SoftwareVsyncSource::NotifyVsync", this,
      &SoftwareVsyncSource::NotifyVsync, nextVsync, outputTime);

  RefPtr<Runnable> addrefedTask = mCurrentVsyncTask;
  mVsyncThread->message_loop()->PostDelayedTask(addrefedTask.forget(),
                                                delay.ToMilliseconds());
}

void SoftwareVsyncSource::Shutdown() {
  MOZ_ASSERT(NS_IsMainThread());
  DisableVsync();
  mVsyncThread->Stop();
  delete mVsyncThread;
  mVsyncThread = nullptr;
}

}  // namespace mozilla::gfx