gecko/layout/base/nsRefreshDriver.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set shiftwidth=2 tabstop=8 autoindent cindent expandtab: */
/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is nsRefreshDriver.
 *
 * The Initial Developer of the Original Code is the Mozilla Foundation.
 * Portions created by the Initial Developer are Copyright (C) 2009
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   L. David Baron <dbaron@dbaron.org>, Mozilla Corporation (original author)
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */

/*
 * Code to notify things that animate before a refresh, at an appropriate
 * refresh rate.  (Perhaps temporary, until replaced by compositor.)
 */

#include "nsRefreshDriver.h"
#include "nsPresContext.h"
#include "nsComponentManagerUtils.h"
#include "prlog.h"
#include "nsAutoPtr.h"

/*
 * TODO:
 * Once this is hooked in to suppressing updates when the presentation
 * is not visible, we need to hook it up to FlushPendingNotifications so
 * that we flush when necessary.
 */

#define REFRESH_INTERVAL_MILLISECONDS 20

using mozilla::TimeStamp;

nsRefreshDriver::nsRefreshDriver(nsPresContext *aPresContext)
  : mPresContext(aPresContext),
    mFrozen(PR_FALSE)
{
}

nsRefreshDriver::~nsRefreshDriver()
{
  NS_ABORT_IF_FALSE(ObserverCount() == 0,
                    "observers should have unregistered");
  NS_ABORT_IF_FALSE(!mTimer, "timer should be gone");
}

TimeStamp
nsRefreshDriver::MostRecentRefresh() const
{
  const_cast<nsRefreshDriver*>(this)->EnsureTimerStarted();

  return mMostRecentRefresh;
}

PRBool
nsRefreshDriver::AddRefreshObserver(nsARefreshObserver *aObserver,
                                    mozFlushType aFlushType)
{
  ObserverArray& array = ArrayFor(aFlushType);
  PRBool success = array.AppendElement(aObserver) != nsnull;

  EnsureTimerStarted();

  return success;
}

PRBool
nsRefreshDriver::RemoveRefreshObserver(nsARefreshObserver *aObserver,
                                       mozFlushType aFlushType)
{
  ObserverArray& array = ArrayFor(aFlushType);
  return array.RemoveElement(aObserver);
}

void
nsRefreshDriver::EnsureTimerStarted()
{
  if (mTimer || mFrozen || !mPresContext) {
    // It's already been started, or we don't want to start it now or
    // we've been disconnected.
    return;
  }

  UpdateMostRecentRefresh();

  mTimer = do_CreateInstance(NS_TIMER_CONTRACTID);
  if (!mTimer) {
    return;
  }

  nsresult rv = mTimer->InitWithCallback(this, REFRESH_INTERVAL_MILLISECONDS,
                                         nsITimer::TYPE_REPEATING_SLACK);
  if (NS_FAILED(rv)) {
    mTimer = nsnull;
  }
}

void
nsRefreshDriver::StopTimer()
{
  if (!mTimer) {
    return;
  }

  mTimer->Cancel();
  mTimer = nsnull;
}

PRUint32
nsRefreshDriver::ObserverCount() const
{
  PRUint32 sum = 0;
  for (PRUint32 i = 0; i < NS_ARRAY_LENGTH(mObservers); ++i) {
    sum += mObservers[i].Length();
  }
  return sum;
}

void
nsRefreshDriver::UpdateMostRecentRefresh()
{
  mMostRecentRefresh = TimeStamp::Now();
}

nsRefreshDriver::ObserverArray&
nsRefreshDriver::ArrayFor(mozFlushType aFlushType)
{
  switch (aFlushType) {
    case Flush_Style:
      return mObservers[0];
    case Flush_Layout:
      return mObservers[1];
    case Flush_Display:
      return mObservers[2];
    default:
      NS_ABORT_IF_FALSE(PR_FALSE, "bad flush type");
      return *static_cast<ObserverArray*>(nsnull);
  }
}

/*
 * nsISupports implementation
 */

NS_IMPL_ISUPPORTS1(nsRefreshDriver, nsITimerCallback)

/*
 * nsITimerCallback implementation
 */

NS_IMETHODIMP
nsRefreshDriver::Notify(nsITimer * /* unused */)
{
  NS_PRECONDITION(!mFrozen, "Why are we notified while frozen?");
  NS_PRECONDITION(mPresContext, "Why are we notified after disconnection?");

  UpdateMostRecentRefresh();

  nsCOMPtr<nsIPresShell> presShell = mPresContext->GetPresShell();
  if (!presShell || ObserverCount() == 0) {
    // Things are being destroyed, or we no longer have any observers.
    // We don't want to stop the timer when observers are initially
    // removed, because sometimes observers can be added and removed
    // often depending on what other things are going on and in that
    // situation we don't want to thrash our timer.  So instead we
    // wait until we get a Notify() call when we have no observers
    // before stopping the timer.
    StopTimer();
    return NS_OK;
  }

  /*
   * The timer holds a reference to |this| while calling |Notify|.
   * However, implementations of |WillRefresh| are permitted to destroy
   * the pres context, which will cause our |mPresContext| to become
   * null.  If this happens, we must stop notifying observers.
   */
  for (PRUint32 i = 0; i < NS_ARRAY_LENGTH(mObservers); ++i) {
    ObserverArray::EndLimitedIterator etor(mObservers[i]);
    while (etor.HasMore()) {
      nsRefPtr<nsARefreshObserver> obs = etor.GetNext();
      obs->WillRefresh(mMostRecentRefresh);
      
      if (!mPresContext || !mPresContext->GetPresShell()) {
        StopTimer();
        return NS_OK;
      }
    }
    if (i == 0) {
      // This is the Flush_Style case.
      // FIXME: Maybe we should only flush if the WillRefresh calls did
      // something?  It's probably ok as-is, though, especially as we
      // hook up more things here (or to the replacement of this class).
      // FIXME: We should probably flush for other sets of observers
      // too.  But we should only flush layout once nsRefreshDriver is
      // the driver for the interruptible layout timer (and we should
      // then Flush_InterruptibleLayout).
      presShell->FlushPendingNotifications(Flush_Style);
    }
  }

  return NS_OK;
}

void
nsRefreshDriver::Freeze()
{
  NS_ASSERTION(!mFrozen, "Freeze called on already-frozen refresh driver");
  StopTimer();
  mFrozen = PR_TRUE;
}

void
nsRefreshDriver::Thaw()
{
  NS_ASSERTION(mFrozen, "Thaw called on an unfrozen refresh driver");
  mFrozen = PR_FALSE;
  if (ObserverCount()) {
    NS_DispatchToCurrentThread(NS_NEW_RUNNABLE_METHOD(nsRefreshDriver, this,
                                                      DoRefresh));
    EnsureTimerStarted();
  }
}

void
nsRefreshDriver::DoRefresh()
{
  // Don't do a refresh unless we're in a state where we should be refreshing.
  if (!mFrozen && mPresContext && mTimer) {
    Notify(nsnull);
  }
}