// Copyright (c) 2013 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 "ui/gl/vsync_provider.h"

#include "base/logging.h"
#include "base/time.h"

namespace {

// These constants define a reasonable range for a calculated refresh interval.
// Calculating refreshes out of this range will be considered a fatal error.
const int64 kMinVsyncIntervalUs = base::Time::kMicrosecondsPerSecond / 400;
const int64 kMaxVsyncIntervalUs = base::Time::kMicrosecondsPerSecond / 10;

}  // namespace

namespace gfx {

VSyncProvider::VSyncProvider() {
}

VSyncProvider::~VSyncProvider() {
}

SyncControlVSyncProvider::SyncControlVSyncProvider()
    : VSyncProvider(),
      last_media_stream_counter_(0) {
  // On platforms where we can't get an accurate reading on the refresh
  // rate we fall back to the assumption that we're displaying 60 frames
  // per second.
  last_good_interval_ = base::TimeDelta::FromSeconds(1) / 60;
}

SyncControlVSyncProvider::~SyncControlVSyncProvider() {
}

void SyncControlVSyncProvider::GetVSyncParameters(
    const UpdateVSyncCallback& callback) {
#if defined(OS_LINUX)
  base::TimeTicks timebase;

  // The actual clock used for the system time returned by glXGetSyncValuesOML
  // is unspecified. In practice, the clock used is likely to be either
  // CLOCK_REALTIME or CLOCK_MONOTONIC, so we compare the returned time to the
  // current time according to both clocks, and assume that the returned time
  // was produced by the clock whose current time is closest to it, subject
  // to the restriction that the returned time must not be in the future
  // (since it is the time of a vblank that has already occurred).
  int64 system_time;
  int64 media_stream_counter;
  int64 swap_buffer_counter;
  if (!GetSyncValues(&system_time,
                     &media_stream_counter,
                     &swap_buffer_counter))
    return;

  struct timespec real_time;
  struct timespec monotonic_time;
  clock_gettime(CLOCK_REALTIME, &real_time);
  clock_gettime(CLOCK_MONOTONIC, &monotonic_time);

  int64 real_time_in_microseconds =
    real_time.tv_sec * base::Time::kMicrosecondsPerSecond +
    real_time.tv_nsec / base::Time::kNanosecondsPerMicrosecond;
  int64 monotonic_time_in_microseconds =
    monotonic_time.tv_sec * base::Time::kMicrosecondsPerSecond +
    monotonic_time.tv_nsec / base::Time::kNanosecondsPerMicrosecond;

  // We need the time according to CLOCK_MONOTONIC, so if we've been given
  // a time from CLOCK_REALTIME, we need to convert.
  bool time_conversion_needed =
      llabs(system_time - real_time_in_microseconds) <
      llabs(system_time - monotonic_time_in_microseconds);

  if (time_conversion_needed)
    system_time += monotonic_time_in_microseconds - real_time_in_microseconds;

  // Return if |system_time| is more than 1 frames in the future.
  int64 interval_in_microseconds = last_good_interval_.InMicroseconds();
  if (system_time > monotonic_time_in_microseconds + interval_in_microseconds)
    return;

  // If |system_time| is slightly in the future, adjust it to the previous
  // frame and use the last frame counter to prevent issues in the callback.
  if (system_time > monotonic_time_in_microseconds) {
    system_time -= interval_in_microseconds;
    media_stream_counter--;
  }

  timebase = base::TimeTicks::FromInternalValue(system_time);

  int32 numerator, denominator;
  if (GetMscRate(&numerator, &denominator)) {
    last_good_interval_ =
        base::TimeDelta::FromSeconds(denominator) / numerator;
  } else if (!last_timebase_.is_null()) {
    base::TimeDelta timebase_diff = timebase - last_timebase_;
    uint64 counter_diff = media_stream_counter -
        last_media_stream_counter_;
    if (counter_diff > 0 && timebase > last_timebase_)
      last_good_interval_ = timebase_diff / counter_diff;
  }
  if (last_good_interval_.InMicroseconds() < kMinVsyncIntervalUs ||
      last_good_interval_.InMicroseconds() > kMaxVsyncIntervalUs) {
    LOG(FATAL) << "Calculated bogus refresh interval of "
               << last_good_interval_.InMicroseconds() << " us.";
  }

  last_timebase_ = timebase;
  last_media_stream_counter_ = media_stream_counter;
  callback.Run(timebase, last_good_interval_);
#endif  // defined(OS_LINUX)
}

}  // namespace gfx