engine/shell/platform/android/io/flutter/view/VsyncWaiter.java

// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package io.flutter.view;

import android.support.annotation.NonNull;
import android.view.Choreographer;
import android.view.WindowManager;

import io.flutter.Log;
import io.flutter.embedding.engine.FlutterJNI;

// TODO(mattcarroll): add javadoc.
public class VsyncWaiter {
    private static VsyncWaiter instance;

    @NonNull
    public static VsyncWaiter getInstance(@NonNull WindowManager windowManager) {
        if (instance == null) {
            instance = new VsyncWaiter(windowManager);
        }
        return instance;
    }

    @NonNull
    private final WindowManager windowManager;

    private final FlutterJNI.AsyncWaitForVsyncDelegate asyncWaitForVsyncDelegate = new FlutterJNI.AsyncWaitForVsyncDelegate() {
        @Override
        public void asyncWaitForVsync(long cookie) {
            Choreographer.getInstance().postFrameCallback(new Choreographer.FrameCallback() {
                @Override
                public void doFrame(long frameTimeNanos) {
                    float fps = windowManager.getDefaultDisplay().getRefreshRate();
                    long refreshPeriodNanos = (long) (1000000000.0 / fps);
                    FlutterJNI.nativeOnVsync(frameTimeNanos, frameTimeNanos + refreshPeriodNanos, cookie);
                }
            });
        }
    };

    private VsyncWaiter(@NonNull WindowManager windowManager) {
        this.windowManager = windowManager;
    }

    public void init() {
        FlutterJNI.setAsyncWaitForVsyncDelegate(asyncWaitForVsyncDelegate);

        // TODO(mattcarroll): look into moving FPS reporting to a plugin
        float fps = windowManager.getDefaultDisplay().getRefreshRate();
        FlutterJNI.setRefreshRateFPS(fps);
    }
}