content/browser/media/capture/smooth_event_sampler.cc - Issue 1162863003: Move ContentVideoCaptureDeviceCore from src/content to src/media

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Issue 1162863003: Move ContentVideoCaptureDeviceCore from src/content to src/media (Closed) Base URL: https://chromium.googlesource.com/chromium/src.git@master

Patch Set: rebase Created 5 years, 6 months ago

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1 // Copyright (c) 2015 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 "content/browser/media/capture/smooth_event_sampler.h"

6

7 #include <algorithm>

8

9 #include "base/trace_event/trace_event.h"

10

11 namespace content {

12

13 namespace {

14

15 // The maximum amount of time that can elapse before considering unchanged

16 // content as dirty for the purposes of timer-based overdue sampling. This is

17 // the same value found in cc::FrameRateCounter.

18 const int kOverdueDirtyThresholdMillis = 250; // 4 FPS

19

20 } // anonymous namespace

21

22 SmoothEventSampler::SmoothEventSampler(base::TimeDelta min_capture_period,

23 int redundant_capture_goal)

24 : redundant_capture_goal_(redundant_capture_goal),

25 overdue_sample_count_(0),

26 token_bucket_(base::TimeDelta::Max()) {

27 SetMinCapturePeriod(min_capture_period);

28 }

29

30 void SmoothEventSampler::SetMinCapturePeriod(base::TimeDelta period) {

31 DCHECK_GT(period, base::TimeDelta());

32 min_capture_period_ = period;

33 token_bucket_capacity_ = period + period / 2;

34 token_bucket_ = std::min(token_bucket_capacity_, token_bucket_);

35 }

36

37 void SmoothEventSampler::ConsiderPresentationEvent(base::TimeTicks event_time) {

38 DCHECK(!event_time.is_null());

39

40 // Add tokens to the bucket based on advancement in time. Then, re-bound the

41 // number of tokens in the bucket. Overflow occurs when there is too much

42 // time between events (a common case), or when RecordSample() is not being

43 // called often enough (a bug). On the other hand, if RecordSample() is being

44 // called too often (e.g., as a reaction to IsOverdueForSamplingAt()), the

45 // bucket will underflow.

46 if (!current_event_.is_null()) {

47 if (current_event_ < event_time) {

48 token_bucket_ += event_time - current_event_;

49 if (token_bucket_ > token_bucket_capacity_)

50 token_bucket_ = token_bucket_capacity_;

51 }

52 TRACE_COUNTER1("gpu.capture",

53 "MirroringTokenBucketUsec",

54 std::max<int64>(0, token_bucket_.InMicroseconds()));

55 }

56 current_event_ = event_time;

57 }

58

59 bool SmoothEventSampler::ShouldSample() const {

60 return token_bucket_ >= min_capture_period_;

61 }

62

63 void SmoothEventSampler::RecordSample() {

64 token_bucket_ -= min_capture_period_;

65 if (token_bucket_ < base::TimeDelta())

66 token_bucket_ = base::TimeDelta();

67 TRACE_COUNTER1("gpu.capture",

68 "MirroringTokenBucketUsec",

69 std::max<int64>(0, token_bucket_.InMicroseconds()));

70

71 if (HasUnrecordedEvent()) {

72 last_sample_ = current_event_;

73 overdue_sample_count_ = 0;

74 } else {

75 ++overdue_sample_count_;

76 }

77 }

78

79 bool SmoothEventSampler::IsOverdueForSamplingAt(base::TimeTicks event_time)

80 const {

81 DCHECK(!event_time.is_null());

82

83 if (!HasUnrecordedEvent() && overdue_sample_count_ >= redundant_capture_goal_)

84 return false; // Not dirty.

85

86 if (last_sample_.is_null())

87 return true;

88

89 // If we're dirty but not yet old, then we've recently gotten updates, so we

90 // won't request a sample just yet.

91 base::TimeDelta dirty_interval = event_time - last_sample_;

92 return dirty_interval >=

93 base::TimeDelta::FromMilliseconds(kOverdueDirtyThresholdMillis);

94 }

95

96 bool SmoothEventSampler::HasUnrecordedEvent() const {

97 return !current_event_.is_null() && current_event_ != last_sample_;

98 }

99

100 } // namespace content

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