1 /*
2  * Copyright (C) 2021 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 #pragma once
17 
18 #include <optional>
19 
20 #include "media/Pose.h"
21 
22 namespace android {
23 namespace media {
24 
25 /**
26  * Combines world-to-head pose with world-to-screen pose to obtain screen-to-head.
27  *
28  * Input poses may arrive separately. The last pose of each kind is taken into account. The
29  * timestamp of the output is the ealier (older) timestamp of the two inputs.
30  *
31  * Output may be nullopt in the following cases:
32  * - Either one of the inputs has not yet been provided.
33  * - It is estimated that the user is no longer facing the screen.
34  *
35  * Typical usage:
36  *
37  * ScreenHeadFusion fusion(...);
38  * fusion.setWorldToHeadPose(...);
39  * fusion.setWorldToScreenPose(...);
40  * auto output = fusion.calculate();
41  *
42  * This class is not thread-safe, but thread-compatible.
43  */
44 class ScreenHeadFusion {
45   public:
46     struct TimestampedPose {
47         int64_t timestamp;
48         Pose3f pose;
49     };
50 
51     void setWorldToHeadPose(int64_t timestamp, const Pose3f& worldToHead);
52 
53     void setWorldToScreenPose(int64_t timestamp, const Pose3f& worldToScreen);
54 
55     /**
56      * Returns the screen-to-head pose, or nullopt if invalid.
57      */
58     std::optional<TimestampedPose> calculate();
59 
60   private:
61     std::optional<TimestampedPose> mWorldToHead;
62     std::optional<TimestampedPose> mWorldToScreen;
63 };
64 
65 }  // namespace media
66 }  // namespace android
67