Use estimated vsync period on Android

ui/android/java/src/org/chromium/ui/VSyncMonitor.java

 // Copyright 2014 The Chromium 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 org.chromium.ui;
 
 import android.annotation.SuppressLint;
 import android.content.Context;
 import android.os.Build;
 import android.os.Handler;
 import android.view.Choreographer;
 import android.view.WindowManager;
 
 import org.chromium.base.TraceEvent;
 
 /**
  * Notifies clients of the default displays's vertical sync pulses.
  * On ICS, VSyncMonitor relies on setVSyncPointForICS() being called to set a reasonable
  * approximation of a vertical sync starting point; see also http://crbug.com/156397.
  */
 @SuppressLint("NewApi")
 public class VSyncMonitor {
     private static final long NANOSECONDS_PER_SECOND = 1000000000;
     private static final long NANOSECONDS_PER_MILLISECOND = 1000000;
     private static final long NANOSECONDS_PER_MICROSECOND = 1000;
 
+    private static final long MAX_VALID_VSYNC_PERIOD_NANOSECONDS = NANOSECONDS_PER_SECOND / 30;
+
     private boolean mInsideVSync = false;
+    private boolean mConsecutiveVSync = false;

[no sievers, 2014/10/03 18:14:54]

nit: Can you put a comment that this is a conservative guess? Since it relies on
us requesting the next tick from inside the callback, which is currently the
case (but there is maybe no good reason to rely on that - it's fine for now I'd
guess we'd have to make it more complicated to detect it otherwise... such as
always requesting an extra tick internally, without necessarily forwarding it to
the requester, before we go idle).

 
     /**
      * VSync listener class
      */
     public interface Listener {
         /**
          * Called very soon after the start of the display's vertical sync period.
          * @param monitor The VSyncMonitor that triggered the signal.
          * @param vsyncTimeMicros Absolute frame time in microseconds.
          */
         public void onVSync(VSyncMonitor monitor, long vsyncTimeMicros);
     }
 
     private Listener mListener;
 
     // Display refresh rate as reported by the system.
-    private final long mRefreshPeriodNano;
+    private long mRefreshPeriodNano;
 
     private boolean mHaveRequestInFlight;
 
     // Choreographer is used to detect vsync on >= JB.
     private final Choreographer mChoreographer;
     private final Choreographer.FrameCallback mVSyncFrameCallback;
 
     // On ICS we just post a task through the handler (http://crbug.com/156397)
     private final Runnable mVSyncRunnableCallback;
     private long mGoodStartingPointNano;
@@ skipping 17 matching lines @@
     /**
      * Constructs a VSyncMonitor
      * @param context The application context.
      * @param listener The listener receiving VSync notifications.
      * @param enableJBVsync Whether to allow Choreographer-based notifications on JB and up.
      */
     public VSyncMonitor(Context context, VSyncMonitor.Listener listener, boolean enableJBVSync) {
         mListener = listener;
         float refreshRate = ((WindowManager) context.getSystemService(Context.WINDOW_SERVICE))
                 .getDefaultDisplay().getRefreshRate();
         if (refreshRate <= 0) refreshRate = 60;

[no sievers, 2014/10/03 18:14:54]

Should we also handle this case with the estimation now (with the only different
that we init mRefreshPeriodNano to 1/60 here while we start with the
sketchy-sounding-but-not-totally-incredible value if 0 < getRefreshRate() < 30)?

         mRefreshPeriodNano = (long) (NANOSECONDS_PER_SECOND / refreshRate);
 
         if (enableJBVSync && Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
             // Use Choreographer on JB+ to get notified of vsync.
             mChoreographer = Choreographer.getInstance();
+            final boolean useEstimatedRefreshPeriod =
+                    mRefreshPeriodNano > MAX_VALID_VSYNC_PERIOD_NANOSECONDS;
             mVSyncFrameCallback = new Choreographer.FrameCallback() {
                 @Override
                 public void doFrame(long frameTimeNanos) {
                     TraceEvent.begin("VSync");
+                    if (useEstimatedRefreshPeriod && mConsecutiveVSync) {
+                        // Display.getRefreshRate() is unreliable on some platforms.
+                        // Adjust refresh period- initial value is based on Display.getRefreshRate()
+                        // after that it asymptotically approaches the real value.
+                        long lastRefreshDurationNano = frameTimeNanos - mGoodStartingPointNano;
+                        float lastRefreshDurationWeight = 0.75f;

[no sievers, 2014/10/03 18:14:54]

Sorry I meant to use the bigger weight for mRefreshPeriodNano so that the values
end up being smoother and don't jump around. I'd maybe even use
lastRefreshDurationWeight = 0.1f. Then the value after 19 samples should match
the simple moving average (lastRefreshDurationWeight = 1 - (2 / (N + 1))) for a
window size of N = 19.

+                        mRefreshPeriodNano += (long) (lastRefreshDurationWeight *
+                                (lastRefreshDurationNano - mRefreshPeriodNano));
+                    }
                     mGoodStartingPointNano = frameTimeNanos;
                     onVSyncCallback(frameTimeNanos, getCurrentNanoTime());
                     TraceEvent.end("VSync");
                 }
             };
             mVSyncRunnableCallback = null;
         } else {
             // On ICS we just hope that running tasks is relatively predictable.
             mChoreographer = null;
             mVSyncFrameCallback = null;
@@ skipping 77 matching lines @@
         } finally {
             mInsideVSync = false;
         }
     }
 
     private void postCallback() {
         if (mHaveRequestInFlight) return;
         mHaveRequestInFlight = true;
         if (postSyntheticVSync()) return;
         if (isVSyncSignalAvailable()) {
+            mConsecutiveVSync = mInsideVSync;
             mChoreographer.postFrameCallback(mVSyncFrameCallback);
         } else {
             postRunnableCallback();
         }
     }
 
     private boolean postSyntheticVSync() {
         final long currentTime = getCurrentNanoTime();
         // Only trigger a synthetic vsync if we've been idle for long enough and the upcoming real
         // vsync is more than half a frame away.
@@ skipping 18 matching lines @@
 
         if (currentTime + delay <= mLastPostedNano + mRefreshPeriodNano / 2) {
             delay += mRefreshPeriodNano;
         }
 
         mLastPostedNano = currentTime + delay;
         if (delay == 0) mHandler.post(mVSyncRunnableCallback);
         else mHandler.postDelayed(mVSyncRunnableCallback, delay / NANOSECONDS_PER_MILLISECOND);
     }
 }