1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
|
/*
* Copyright (C) 2022 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "FrameRateAligner.h"
namespace WebCore {
DEFINE_ALLOCATOR_WITH_HEAP_IDENTIFIER(FrameRateAligner);
FrameRateAligner::FrameRateAligner() = default;
FrameRateAligner::~FrameRateAligner() = default;
static ReducedResolutionSeconds idealTimeForNextUpdate(ReducedResolutionSeconds firstUpdateTime, ReducedResolutionSeconds lastUpdateTime, FramesPerSecond frameRate)
{
ReducedResolutionSeconds interval(1.0 / frameRate);
auto timeUntilNextUpdate = (lastUpdateTime - firstUpdateTime) % interval;
return lastUpdateTime + interval - timeUntilNextUpdate;
}
void FrameRateAligner::beginUpdate(ReducedResolutionSeconds timestamp, std::optional<FramesPerSecond> timelineFrameRate)
{
// We record the timestamp for this new update such that in updateFrameRate()
// we can compare against it to identify animations that should be sampled
// for this current update.
m_timestamp = timestamp;
const auto nextUpdateTimeEpsilon = 1_ms;
for (auto& [frameRate, data] : m_frameRates) {
// We can reset isNew to false for all entries since they were already present
// in the previous update.
data.isNew = false;
// If the timeline frame rate is the same as this animation frame rate, then
// we don't need to compute the next ideal sample time.
if (timelineFrameRate == frameRate) {
data.lastUpdateTime = timestamp;
continue;
}
// If the next ideal sample time for this frame rate aligns with the current timestamp
// or is already behind the current timestamp, we can set the last update time to the
// current timestamp, which will indicate in updateFrameRate() that animations using
// this frame rate should be sampled in the current update.
auto nextUpdateTime = idealTimeForNextUpdate(data.firstUpdateTime, data.lastUpdateTime, frameRate);
if ((nextUpdateTime - nextUpdateTimeEpsilon) <= timestamp)
data.lastUpdateTime = timestamp;
}
}
auto FrameRateAligner::updateFrameRate(FramesPerSecond frameRate) -> ShouldUpdate
{
auto it = m_frameRates.find(frameRate);
if (it != m_frameRates.end()) {
// We're dealing with a frame rate for which we've sampled animations before.
// If the last update time for this frame rate is the current timestamp, this
// means we've established in beginUpdate() that animations for this frame rate
// should be sampled.
return it->value.lastUpdateTime == m_timestamp ? ShouldUpdate::Yes : ShouldUpdate::No;
}
// We're dealing with a frame rate we didn't see in the previous update. In this case,
// we'll allow animations to be sampled right away. Later, in finishUpdate(), we'll
// make sure to reset the last update time to align this new frame rate with other
// compatible frame rates.
m_frameRates.set(frameRate, FrameRateData { m_timestamp, m_timestamp });
return ShouldUpdate::Yes;
}
// For two frame rates to be aligned, one must be the multitple of the other, or vice versa.
static bool frameRatesCanBeAligned(FramesPerSecond a, FramesPerSecond b)
{
return (a > b && a % b == 0) || (b > a && b % a == 0);
}
void FrameRateAligner::finishUpdate()
{
// Iterate through the frame rates to find new entries and set their first update time
// in a way that future updates will be synchronized with other animations with that
// frame rate.
for (auto& [frameRate, data] : m_frameRates) {
if (!data.isNew)
continue;
// Look for the compatible frame rate with the highest value.
std::optional<FramesPerSecond> highestCompatibleFrameRate;
for (auto& [potentiallyCompatibleFrameRate, potentiallyCompatibleData] : m_frameRates) {
if (potentiallyCompatibleData.isNew)
continue;
if (frameRatesCanBeAligned(frameRate, potentiallyCompatibleFrameRate)) {
if (!highestCompatibleFrameRate || *highestCompatibleFrameRate > potentiallyCompatibleFrameRate)
highestCompatibleFrameRate = potentiallyCompatibleFrameRate;
}
}
// If we don't find any compatible frame rate, we can leave the last update time as-is
// and use the current timestamp as the basis from which we'll align animations for this
// frame rate.
if (highestCompatibleFrameRate)
data.firstUpdateTime = m_frameRates.get(*highestCompatibleFrameRate).firstUpdateTime;
}
}
std::optional<Seconds> FrameRateAligner::timeUntilNextUpdateForFrameRate(FramesPerSecond frameRate, ReducedResolutionSeconds timestamp) const
{
auto it = m_frameRates.find(frameRate);
if (it == m_frameRates.end())
return std::nullopt;
auto& data = it->value;
return idealTimeForNextUpdate(data.firstUpdateTime, data.lastUpdateTime, frameRate) - timestamp;
}
std::optional<FramesPerSecond> FrameRateAligner::maximumFrameRate() const
{
std::optional<FramesPerSecond> maximumFrameRate;
for (auto frameRate : m_frameRates.keys()) {
if (!maximumFrameRate || *maximumFrameRate < frameRate)
maximumFrameRate = frameRate;
}
return maximumFrameRate;
}
} // namespace WebCore
|
