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/*
* Copyright 2022 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#define LOG_TAG "CompositorTiming"
#include <cutils/compiler.h>
#include <gui/CompositorTiming.h>
#include <log/log.h>
namespace android::gui {
CompositorTiming::CompositorTiming(nsecs_t vsyncDeadline, nsecs_t vsyncPeriod, nsecs_t vsyncPhase,
nsecs_t presentLatency) {
if (CC_UNLIKELY(vsyncPeriod <= 0)) {
ALOGE("Invalid VSYNC period");
return;
}
const nsecs_t idealLatency = [=] {
// Modulo rounds toward 0 not INT64_MIN, so treat signs separately.
if (vsyncPhase < 0) return -vsyncPhase % vsyncPeriod;
const nsecs_t latency = (vsyncPeriod - vsyncPhase) % vsyncPeriod;
return latency > 0 ? latency : vsyncPeriod;
}();
// Snap the latency to a value that removes scheduling jitter from the composite and present
// times, which often have >1ms of jitter. Reducing jitter is important if an app attempts to
// extrapolate something like user input to an accurate present time. Snapping also allows an
// app to precisely calculate vsyncPhase with (presentLatency % interval).
const nsecs_t bias = vsyncPeriod / 2;
const nsecs_t extraVsyncs = (presentLatency - idealLatency + bias) / vsyncPeriod;
const nsecs_t snappedLatency =
extraVsyncs > 0 ? idealLatency + extraVsyncs * vsyncPeriod : idealLatency;
this->deadline = vsyncDeadline - idealLatency;
this->interval = vsyncPeriod;
this->presentLatency = snappedLatency;
}
} // namespace android::gui
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