Line data    Source code

       1             : /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
       2             : /* vim: set shiftwidth=2 tabstop=8 autoindent cindent expandtab: */
       3             : /* This Source Code Form is subject to the terms of the Mozilla Public
       4             :  * License, v. 2.0. If a copy of the MPL was not distributed with this
       5             :  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
       6             : 
       7             : #include "ScrollVelocityQueue.h"
       8             : 
       9             : #include "gfxPrefs.h"
      10             : #include "nsPresContext.h"
      11             : #include "nsRefreshDriver.h"
      12             : 
      13             : namespace mozilla {
      14             : namespace layout {
      15             : 
      16             : void
      17           0 : ScrollVelocityQueue::Sample(const nsPoint& aScrollPosition)
      18             : {
      19           0 :   float flingSensitivity = gfxPrefs::ScrollSnapPredictionSensitivity();
      20           0 :   int maxVelocity = gfxPrefs::ScrollSnapPredictionMaxVelocity();
      21           0 :   maxVelocity = nsPresContext::CSSPixelsToAppUnits(maxVelocity);
      22           0 :   int maxOffset = maxVelocity * flingSensitivity;
      23           0 :   TimeStamp currentRefreshTime = mPresContext->RefreshDriver()->MostRecentRefresh();
      24           0 :   if (mSampleTime.IsNull()) {
      25           0 :     mAccumulator = nsPoint();
      26             :   } else {
      27           0 :     uint32_t durationMs = (currentRefreshTime - mSampleTime).ToMilliseconds();
      28           0 :     if (durationMs > gfxPrefs::APZVelocityRelevanceTime()) {
      29           0 :       mAccumulator = nsPoint();
      30           0 :       mQueue.Clear();
      31           0 :     } else if (durationMs == 0) {
      32           0 :       mAccumulator += aScrollPosition - mLastPosition;
      33             :     } else {
      34           0 :       nsPoint velocity = mAccumulator * 1000 / durationMs;
      35           0 :       velocity.Clamp(maxVelocity);
      36           0 :       mQueue.AppendElement(std::make_pair(durationMs, velocity));
      37           0 :       mAccumulator = aScrollPosition - mLastPosition;
      38             :     }
      39             :   }
      40           0 :   mAccumulator.Clamp(maxOffset);
      41           0 :   mSampleTime = currentRefreshTime;
      42           0 :   mLastPosition = aScrollPosition;
      43           0 :   TrimQueue();
      44           0 : }
      45             : 
      46             : void
      47           0 : ScrollVelocityQueue::TrimQueue()
      48             : {
      49           0 :   if (mSampleTime.IsNull()) {
      50             :     // There are no samples, nothing to do here.
      51           0 :     return;
      52             :   }
      53             : 
      54           0 :   TimeStamp currentRefreshTime = mPresContext->RefreshDriver()->MostRecentRefresh();
      55           0 :   nsPoint velocity;
      56           0 :   uint32_t timeDelta = (currentRefreshTime - mSampleTime).ToMilliseconds();
      57           0 :   for (int i = mQueue.Length() - 1; i >= 0; i--) {
      58           0 :     timeDelta += mQueue[i].first;
      59           0 :     if (timeDelta >= gfxPrefs::APZVelocityRelevanceTime()) {
      60             :       // The rest of the samples have expired and should be dropped
      61           0 :       for (; i >= 0; i--) {
      62           0 :         mQueue.RemoveElementAt(0);
      63             :       }
      64             :     }
      65             :   }
      66             : }
      67             : 
      68             : void
      69           0 : ScrollVelocityQueue::Reset()
      70             : {
      71           0 :   mAccumulator = nsPoint();
      72           0 :   mSampleTime = TimeStamp();
      73           0 :   mQueue.Clear();
      74           0 : }
      75             : 
      76             : /**
      77             :   Calculate the velocity of the scroll frame, in appunits / second.
      78             : */
      79             : nsPoint
      80           0 : ScrollVelocityQueue::GetVelocity()
      81             : {
      82           0 :   TrimQueue();
      83           0 :   if (mQueue.Length() == 0) {
      84             :     // If getting the scroll velocity before any scrolling has occurred,
      85             :     // the velocity must be (0, 0)
      86           0 :     return nsPoint();
      87             :   }
      88           0 :   nsPoint velocity;
      89           0 :   for (int i = mQueue.Length() - 1; i >= 0; i--) {
      90           0 :     velocity += mQueue[i].second;
      91             :   }
      92           0 :   return velocity / mQueue.Length();;
      93             : }
      94             : 
      95             : } // namespace layout
      96             : } // namespace mozilla
      97             :