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      1 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "ui/gl/vsync_provider.h"
      6 
      7 #include <math.h>
      8 
      9 #include "base/logging.h"
     10 #include "base/time/time.h"
     11 
     12 namespace {
     13 
     14 // These constants define a reasonable range for a calculated refresh interval.
     15 // Calculating refreshes out of this range will be considered a fatal error.
     16 const int64 kMinVsyncIntervalUs = base::Time::kMicrosecondsPerSecond / 400;
     17 const int64 kMaxVsyncIntervalUs = base::Time::kMicrosecondsPerSecond / 10;
     18 
     19 // How much noise we'll tolerate between successive computed intervals before
     20 // we think the latest computed interval is invalid (noisey due to
     21 // monitor configuration change, moving a window between monitors, etc.).
     22 const double kRelativeIntervalDifferenceThreshold = 0.05;
     23 
     24 }  // namespace
     25 
     26 namespace gfx {
     27 
     28 VSyncProvider::VSyncProvider() {
     29 }
     30 
     31 VSyncProvider::~VSyncProvider() {
     32 }
     33 
     34 SyncControlVSyncProvider::SyncControlVSyncProvider()
     35     : VSyncProvider(),
     36       last_media_stream_counter_(0) {
     37   // On platforms where we can't get an accurate reading on the refresh
     38   // rate we fall back to the assumption that we're displaying 60 frames
     39   // per second.
     40   last_good_interval_ = base::TimeDelta::FromSeconds(1) / 60;
     41 }
     42 
     43 SyncControlVSyncProvider::~SyncControlVSyncProvider() {
     44 }
     45 
     46 void SyncControlVSyncProvider::GetVSyncParameters(
     47     const UpdateVSyncCallback& callback) {
     48 #if defined(OS_LINUX)
     49   base::TimeTicks timebase;
     50 
     51   // The actual clock used for the system time returned by glXGetSyncValuesOML
     52   // is unspecified. In practice, the clock used is likely to be either
     53   // CLOCK_REALTIME or CLOCK_MONOTONIC, so we compare the returned time to the
     54   // current time according to both clocks, and assume that the returned time
     55   // was produced by the clock whose current time is closest to it, subject
     56   // to the restriction that the returned time must not be in the future
     57   // (since it is the time of a vblank that has already occurred).
     58   int64 system_time;
     59   int64 media_stream_counter;
     60   int64 swap_buffer_counter;
     61   if (!GetSyncValues(&system_time,
     62                      &media_stream_counter,
     63                      &swap_buffer_counter))
     64     return;
     65 
     66   // Both Intel and Mali drivers will return TRUE for GetSyncValues
     67   // but a value of 0 for MSC if they cannot access the CRTC data structure
     68   // associated with the surface. crbug.com/231945
     69   if (media_stream_counter == 0) {
     70     LOG(ERROR) << "glXGetSyncValuesOML should not return TRUE with a "
     71                << "media stream counter of 0.";
     72     return;
     73   }
     74 
     75   struct timespec real_time;
     76   struct timespec monotonic_time;
     77   clock_gettime(CLOCK_REALTIME, &real_time);
     78   clock_gettime(CLOCK_MONOTONIC, &monotonic_time);
     79 
     80   int64 real_time_in_microseconds =
     81     real_time.tv_sec * base::Time::kMicrosecondsPerSecond +
     82     real_time.tv_nsec / base::Time::kNanosecondsPerMicrosecond;
     83   int64 monotonic_time_in_microseconds =
     84     monotonic_time.tv_sec * base::Time::kMicrosecondsPerSecond +
     85     monotonic_time.tv_nsec / base::Time::kNanosecondsPerMicrosecond;
     86 
     87   // We need the time according to CLOCK_MONOTONIC, so if we've been given
     88   // a time from CLOCK_REALTIME, we need to convert.
     89   bool time_conversion_needed =
     90       llabs(system_time - real_time_in_microseconds) <
     91       llabs(system_time - monotonic_time_in_microseconds);
     92 
     93   if (time_conversion_needed)
     94     system_time += monotonic_time_in_microseconds - real_time_in_microseconds;
     95 
     96   // Return if |system_time| is more than 1 frames in the future.
     97   int64 interval_in_microseconds = last_good_interval_.InMicroseconds();
     98   if (system_time > monotonic_time_in_microseconds + interval_in_microseconds)
     99     return;
    100 
    101   // If |system_time| is slightly in the future, adjust it to the previous
    102   // frame and use the last frame counter to prevent issues in the callback.
    103   if (system_time > monotonic_time_in_microseconds) {
    104     system_time -= interval_in_microseconds;
    105     media_stream_counter--;
    106   }
    107   if (monotonic_time_in_microseconds - system_time >
    108       base::Time::kMicrosecondsPerSecond)
    109     return;
    110 
    111   timebase = base::TimeTicks::FromInternalValue(system_time);
    112 
    113   // Only need the previous calculated interval for our filtering.
    114   while (last_computed_intervals_.size() > 1)
    115     last_computed_intervals_.pop();
    116 
    117   int32 numerator, denominator;
    118   if (GetMscRate(&numerator, &denominator)) {
    119     last_computed_intervals_.push(
    120         base::TimeDelta::FromSeconds(denominator) / numerator);
    121   } else if (!last_timebase_.is_null()) {
    122     base::TimeDelta timebase_diff = timebase - last_timebase_;
    123     int64 counter_diff = media_stream_counter -
    124         last_media_stream_counter_;
    125     if (counter_diff > 0 && timebase > last_timebase_)
    126       last_computed_intervals_.push(timebase_diff / counter_diff);
    127   }
    128 
    129   if (last_computed_intervals_.size() == 2) {
    130     const base::TimeDelta& old_interval = last_computed_intervals_.front();
    131     const base::TimeDelta& new_interval = last_computed_intervals_.back();
    132 
    133     double relative_change =
    134         fabs(old_interval.InMillisecondsF() - new_interval.InMillisecondsF()) /
    135         new_interval.InMillisecondsF();
    136     if (relative_change < kRelativeIntervalDifferenceThreshold) {
    137       if (new_interval.InMicroseconds() < kMinVsyncIntervalUs ||
    138           new_interval.InMicroseconds() > kMaxVsyncIntervalUs) {
    139         LOG(FATAL) << "Calculated bogus refresh interval of "
    140                    << new_interval.InMicroseconds() << " us. "
    141                    << "Last time base of "
    142                    << last_timebase_.ToInternalValue() << " us. "
    143                    << "Current time base of "
    144                    << timebase.ToInternalValue() << " us. "
    145                    << "Last media stream count of "
    146                    << last_media_stream_counter_ << ". "
    147                    << "Current media stream count of "
    148                    << media_stream_counter << ".";
    149       } else {
    150         last_good_interval_ = new_interval;
    151       }
    152     }
    153   }
    154 
    155   last_timebase_ = timebase;
    156   last_media_stream_counter_ = media_stream_counter;
    157   callback.Run(timebase, last_good_interval_);
    158 #endif  // defined(OS_LINUX)
    159 }
    160 
    161 }  // namespace gfx
    162