1 /*
2 * Copyright (C) 2022 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #pragma once
18
19 #include <array>
20 #include <cstdint>
21 #include <memory>
22 #include <mutex>
23 #include <optional>
24 #include <string>
25 #include <unordered_map>
26
27 #include <android-base/result.h>
28 #include <android-base/thread_annotations.h>
29 #include <android/sysprop/InputProperties.sysprop.h>
30 #include <input/Input.h>
31 #include <input/MotionPredictorMetricsManager.h>
32 #include <input/RingBuffer.h>
33 #include <input/TfLiteMotionPredictor.h>
34 #include <utils/Timers.h> // for nsecs_t
35
36 namespace android {
37
isMotionPredictionEnabled()38 static inline bool isMotionPredictionEnabled() {
39 return sysprop::InputProperties::enable_motion_prediction().value_or(true);
40 }
41
42 // Tracker to calculate jerk from motion position samples.
43 class JerkTracker {
44 public:
45 // Initialize the tracker. If normalizedDt is true, assume that each sample pushed has dt=1.
46 // alpha is the coefficient of the first-order IIR filter for jerk. A factor of 1 results
47 // in no smoothing.
48 JerkTracker(bool normalizedDt, float alpha);
49
50 // Add a position to the tracker and update derivative estimates.
51 void pushSample(int64_t timestamp, float xPos, float yPos);
52
53 // Reset JerkTracker for a new motion input.
54 void reset();
55
56 // Return last jerk calculation, if enough samples have been collected.
57 // Jerk is defined as the 3rd derivative of position (change in
58 // acceleration) and has the units of d^3p/dt^3.
59 std::optional<float> jerkMagnitude() const;
60
61 private:
62 const bool mNormalizedDt;
63 // Coefficient of first-order IIR filter to smooth jerk calculation.
64 const float mAlpha;
65
66 RingBuffer<int64_t> mTimestamps{4};
67 std::array<float, 4> mXDerivatives{}; // [x, x', x'', x''']
68 std::array<float, 4> mYDerivatives{}; // [y, y', y'', y''']
69 float mJerkMagnitude;
70 };
71
72 /**
73 * Given a set of MotionEvents for the current gesture, predict the motion. The returned MotionEvent
74 * contains a set of samples in the future.
75 *
76 * The typical usage is like this:
77 *
78 * MotionPredictor predictor(offset = MY_OFFSET);
79 * predictor.record(DOWN_MOTION_EVENT);
80 * predictor.record(MOVE_MOTION_EVENT);
81 * prediction = predictor.predict(futureTime);
82 *
83 * The resulting motion event will have eventTime <= (futureTime + MY_OFFSET). It might contain
84 * historical data, which are additional samples from the latest recorded MotionEvent's eventTime
85 * to the futureTime + MY_OFFSET.
86 *
87 * The offset is used to provide additional flexibility to the caller, in case the default present
88 * time (typically provided by the choreographer) does not account for some delays, or to simply
89 * reduce the aggressiveness of the prediction. Offset can be positive or negative.
90 */
91 class MotionPredictor {
92 public:
93 using ReportAtomFunction = MotionPredictorMetricsManager::ReportAtomFunction;
94
95 /**
96 * Parameters:
97 * predictionTimestampOffsetNanos: additional, constant shift to apply to the target
98 * prediction time. The prediction will target the time t=(prediction time +
99 * predictionTimestampOffsetNanos).
100 *
101 * checkEnableMotionPrediction: the function to check whether the prediction should run. Used to
102 * provide an additional way of turning prediction on and off. Can be toggled at runtime.
103 *
104 * reportAtomFunction: the function that will be called to report prediction metrics. If
105 * omitted, the implementation will choose a default metrics reporting mechanism.
106 */
107 MotionPredictor(nsecs_t predictionTimestampOffsetNanos,
108 std::function<bool()> checkEnableMotionPrediction = isMotionPredictionEnabled,
109 ReportAtomFunction reportAtomFunction = {});
110
111 /**
112 * Record the actual motion received by the view. This event will be used for calculating the
113 * predictions.
114 *
115 * @return empty result if the event was processed correctly, error if the event is not
116 * consistent with the previously recorded events.
117 */
118 android::base::Result<void> record(const MotionEvent& event);
119
120 std::unique_ptr<MotionEvent> predict(nsecs_t timestamp);
121
122 bool isPredictionAvailable(int32_t deviceId, int32_t source);
123
124 private:
125 const nsecs_t mPredictionTimestampOffsetNanos;
126 const std::function<bool()> mCheckMotionPredictionEnabled;
127
128 std::unique_ptr<TfLiteMotionPredictorModel> mModel;
129
130 std::unique_ptr<TfLiteMotionPredictorBuffers> mBuffers;
131 std::optional<MotionEvent> mLastEvent;
132
133 std::unique_ptr<JerkTracker> mJerkTracker;
134
135 std::unique_ptr<MotionPredictorMetricsManager> mMetricsManager;
136
137 const ReportAtomFunction mReportAtomFunction;
138
139 // Initialize prediction model and associated objects.
140 // Called during lazy initialization.
141 // TODO: b/210158587 Consider removing lazy initialization.
142 void initializeObjects();
143 };
144
145 } // namespace android
146