1 /*
2 * Copyright 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 #define LOG_TAG "CompositorTiming"
18
19 #include <cutils/compiler.h>
20 #include <gui/CompositorTiming.h>
21 #include <log/log.h>
22
23 namespace android::gui {
24
CompositorTiming(nsecs_t vsyncDeadline,nsecs_t vsyncPeriod,nsecs_t vsyncPhase,nsecs_t presentLatency)25 CompositorTiming::CompositorTiming(nsecs_t vsyncDeadline, nsecs_t vsyncPeriod, nsecs_t vsyncPhase,
26 nsecs_t presentLatency) {
27 if (CC_UNLIKELY(vsyncPeriod <= 0)) {
28 ALOGE("Invalid VSYNC period");
29 return;
30 }
31
32 const nsecs_t idealLatency = [=] {
33 // Modulo rounds toward 0 not INT64_MIN, so treat signs separately.
34 if (vsyncPhase < 0) return -vsyncPhase % vsyncPeriod;
35
36 const nsecs_t latency = (vsyncPeriod - vsyncPhase) % vsyncPeriod;
37 return latency > 0 ? latency : vsyncPeriod;
38 }();
39
40 // Snap the latency to a value that removes scheduling jitter from the composite and present
41 // times, which often have >1ms of jitter. Reducing jitter is important if an app attempts to
42 // extrapolate something like user input to an accurate present time. Snapping also allows an
43 // app to precisely calculate vsyncPhase with (presentLatency % interval).
44 const nsecs_t bias = vsyncPeriod / 2;
45 const nsecs_t extraVsyncs = (presentLatency - idealLatency + bias) / vsyncPeriod;
46 const nsecs_t snappedLatency =
47 extraVsyncs > 0 ? idealLatency + extraVsyncs * vsyncPeriod : idealLatency;
48
49 this->deadline = vsyncDeadline - idealLatency;
50 this->interval = vsyncPeriod;
51 this->presentLatency = snappedLatency;
52 }
53
54 } // namespace android::gui
55