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diff --git a/services/surfaceflinger/Scheduler/VSyncModulator.h b/services/surfaceflinger/Scheduler/VSyncModulator.h
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+++ b/services/surfaceflinger/Scheduler/VSyncModulator.h
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+/*
+ * Copyright 2018 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.
+ */
+
+#pragma once
+
+#include <chrono>
+#include <mutex>
+
+#include "Scheduler.h"
+
+namespace android::scheduler {
+
+/*
+ * Modulates the vsync-offsets depending on current SurfaceFlinger state.
+ */
+class VSyncModulator {
+private:
+    // Number of frames we'll keep the early phase offsets once they are activated for a
+    // transaction. This acts as a low-pass filter in case the client isn't quick enough in
+    // sending new transactions.
+    static constexpr int MIN_EARLY_FRAME_COUNT_TRANSACTION = 2;
+
+    // Number of frames we'll keep the early gl phase offsets once they are activated.
+    // This acts as a low-pass filter to avoid scenarios where we rapidly
+    // switch in and out of gl composition.
+    static constexpr int MIN_EARLY_GL_FRAME_COUNT_TRANSACTION = 2;
+
+    // Margin used to account for potential data races
+    static const constexpr std::chrono::nanoseconds MARGIN_FOR_TX_APPLY = 1ms;
+
+public:
+    // Wrapper for a collection of surfaceflinger/app offsets for a particular
+    // configuration.
+    struct Offsets {
+        nsecs_t sf;
+        nsecs_t app;
+
+        bool operator==(const Offsets& other) const { return sf == other.sf && app == other.app; }
+
+        bool operator!=(const Offsets& other) const { return !(*this == other); }
+    };
+
+    struct OffsetsConfig {
+        Offsets early;   // For transactions with the eEarlyWakeup flag.
+        Offsets earlyGl; // As above but while compositing with GL.
+        Offsets late;    // Default.
+
+        bool operator==(const OffsetsConfig& other) const {
+            return early == other.early && earlyGl == other.earlyGl && late == other.late;
+        }
+
+        bool operator!=(const OffsetsConfig& other) const { return !(*this == other); }
+    };
+
+    VSyncModulator(IPhaseOffsetControl&, ConnectionHandle appConnectionHandle,
+                   ConnectionHandle sfConnectionHandle, const OffsetsConfig&);
+
+    void setPhaseOffsets(const OffsetsConfig&) EXCLUDES(mMutex);
+
+    // Signals that a transaction has started, and changes offsets accordingly.
+    void setTransactionStart(Scheduler::TransactionStart transactionStart);
+
+    // Signals that a transaction has been completed, so that we can finish
+    // special handling for a transaction.
+    void onTransactionHandled();
+
+    // Called when we send a refresh rate change to hardware composer, so that
+    // we can move into early offsets.
+    void onRefreshRateChangeInitiated();
+
+    // Called when we detect from vsync signals that the refresh rate changed.
+    // This way we can move out of early offsets if no longer necessary.
+    void onRefreshRateChangeCompleted();
+
+    // Called when the display is presenting a new frame. usedRenderEngine
+    // should be set to true if RenderEngine was involved with composing the new
+    // frame.
+    void onRefreshed(bool usedRenderEngine);
+
+    // Returns the offsets that we are currently using
+    Offsets getOffsets() const EXCLUDES(mMutex);
+
+private:
+    friend class VSyncModulatorTest;
+    // Returns the next offsets that we should be using
+    const Offsets& getNextOffsets() const REQUIRES(mMutex);
+    // Updates offsets and persists them into the scheduler framework.
+    void updateOffsets() EXCLUDES(mMutex);
+    void updateOffsetsLocked() REQUIRES(mMutex);
+
+    IPhaseOffsetControl& mPhaseOffsetControl;
+    const ConnectionHandle mAppConnectionHandle;
+    const ConnectionHandle mSfConnectionHandle;
+
+    mutable std::mutex mMutex;
+    OffsetsConfig mOffsetsConfig GUARDED_BY(mMutex);
+
+    Offsets mOffsets GUARDED_BY(mMutex){mOffsetsConfig.late};
+
+    std::atomic<Scheduler::TransactionStart> mTransactionStart =
+            Scheduler::TransactionStart::Normal;
+    std::atomic<bool> mRefreshRateChangePending = false;
+    std::atomic<bool> mExplicitEarlyWakeup = false;
+    std::atomic<int> mRemainingEarlyFrameCount = 0;
+    std::atomic<int> mRemainingRenderEngineUsageCount = 0;
+    std::atomic<std::chrono::steady_clock::time_point> mEarlyTxnStartTime = {};
+    std::atomic<std::chrono::steady_clock::time_point> mTxnAppliedTime = {};
+
+    bool mTraceDetailedInfo = false;
+};
+
+} // namespace android::scheduler