/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* vim: set ts=8 sts=2 et sw=2 tw=80: */

/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "ScrollVelocityQueue.h"

#include "gfxPrefs.h"

#include "nsPresContext.h"

#include "nsRefreshDriver.h"

namespace mozilla {

namespace layout {

void

ScrollVelocityQueue::Sample(const nsPoint& aScrollPosition)

{

  float flingSensitivity = gfxPrefs::ScrollSnapPredictionSensitivity();

  int maxVelocity = gfxPrefs::ScrollSnapPredictionMaxVelocity();

  maxVelocity = nsPresContext::CSSPixelsToAppUnits(maxVelocity);

  int maxOffset = maxVelocity * flingSensitivity;

  TimeStamp currentRefreshTime = mPresContext->RefreshDriver()->MostRecentRefresh();

  if (mSampleTime.IsNull()) {

    mAccumulator = nsPoint();

  } else {

    uint32_t durationMs = (currentRefreshTime - mSampleTime).ToMilliseconds();

    if (durationMs > gfxPrefs::APZVelocityRelevanceTime()) {

      mAccumulator = nsPoint();

      mQueue.Clear();

    } else if (durationMs == 0) {

      mAccumulator += aScrollPosition - mLastPosition;

    } else {

      nsPoint velocity = mAccumulator * 1000 / durationMs;

      velocity.Clamp(maxVelocity);

      mQueue.AppendElement(std::make_pair(durationMs, velocity));

      mAccumulator = aScrollPosition - mLastPosition;

    }

  }

  mAccumulator.Clamp(maxOffset);

  mSampleTime = currentRefreshTime;

  mLastPosition = aScrollPosition;

  TrimQueue();

}

void

ScrollVelocityQueue::TrimQueue()

{

  if (mSampleTime.IsNull()) {

    // There are no samples, nothing to do here.

    return;

  }

  TimeStamp currentRefreshTime = mPresContext->RefreshDriver()->MostRecentRefresh();

  nsPoint velocity;

  uint32_t timeDelta = (currentRefreshTime - mSampleTime).ToMilliseconds();

  for (int i = mQueue.Length() - 1; i >= 0; i--) {

    timeDelta += mQueue[i].first;

    if (timeDelta >= gfxPrefs::APZVelocityRelevanceTime()) {

      // The rest of the samples have expired and should be dropped

      for (; i >= 0; i--) {

        mQueue.RemoveElementAt(0);

      }

    }

  }

}

void

ScrollVelocityQueue::Reset()

{

  mAccumulator = nsPoint();

  mSampleTime = TimeStamp();

  mQueue.Clear();

}

/**

  Calculate the velocity of the scroll frame, in appunits / second.

*/

nsPoint

ScrollVelocityQueue::GetVelocity()

{

  TrimQueue();

  if (mQueue.Length() == 0) {

    // If getting the scroll velocity before any scrolling has occurred,

    // the velocity must be (0, 0)

    return nsPoint();

  }

  nsPoint velocity;

  for (int i = mQueue.Length() - 1; i >= 0; i--) {

    velocity += mQueue[i].second;

  }

  return velocity / mQueue.Length();;

}

} // namespace layout

} // namespace mozilla