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