gecko-dev/layout/xul/nsSliderFrame.cpp

/* -*- 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/. */

//
// Eric Vaughan
// Netscape Communications
//
// See documentation in associated header file
//

#include "nsSliderFrame.h"

#include "gfxPrefs.h"
#include "mozilla/ComputedStyle.h"
#include "nsPresContext.h"
#include "nsIContent.h"
#include "nsCOMPtr.h"
#include "nsNameSpaceManager.h"
#include "nsGkAtoms.h"
#include "nsHTMLParts.h"
#include "nsIPresShell.h"
#include "nsCSSRendering.h"
#include "nsScrollbarButtonFrame.h"
#include "nsIScrollableFrame.h"
#include "nsIScrollbarMediator.h"
#include "nsISupportsImpl.h"
#include "nsScrollbarFrame.h"
#include "nsRepeatService.h"
#include "nsBoxLayoutState.h"
#include "nsSprocketLayout.h"
#include "nsIServiceManager.h"
#include "nsContentUtils.h"
#include "nsLayoutUtils.h"
#include "nsDisplayList.h"
#include "nsRefreshDriver.h"  // for nsAPostRefreshObserver
#include "nsSVGIntegrationUtils.h"
#include "mozilla/Assertions.h"  // for MOZ_ASSERT
#include "mozilla/Preferences.h"
#include "mozilla/LookAndFeel.h"
#include "mozilla/MouseEvents.h"
#include "mozilla/Telemetry.h"
#include "mozilla/dom/Event.h"
#include "mozilla/gfx/gfxVars.h"
#include "mozilla/layers/APZCCallbackHelper.h"
#include "mozilla/layers/AsyncDragMetrics.h"
#include "mozilla/layers/InputAPZContext.h"
#include <algorithm>

using namespace mozilla;
using mozilla::dom::Event;
using mozilla::layers::APZCCallbackHelper;
using mozilla::layers::AsyncDragMetrics;
using mozilla::layers::InputAPZContext;
using mozilla::layers::ScrollbarData;
using mozilla::layers::ScrollDirection;

bool nsSliderFrame::gMiddlePref = false;
int32_t nsSliderFrame::gSnapMultiplier;

// Turn this on if you want to debug slider frames.
#undef DEBUG_SLIDER

static already_AddRefed<nsIContent> GetContentOfBox(nsIFrame* aBox) {
  nsCOMPtr<nsIContent> content = aBox->GetContent();
  return content.forget();
}

nsIFrame* NS_NewSliderFrame(nsIPresShell* aPresShell, ComputedStyle* aStyle) {
  return new (aPresShell) nsSliderFrame(aStyle, aPresShell->GetPresContext());
}

NS_IMPL_FRAMEARENA_HELPERS(nsSliderFrame)

NS_QUERYFRAME_HEAD(nsSliderFrame)
  NS_QUERYFRAME_ENTRY(nsSliderFrame)
NS_QUERYFRAME_TAIL_INHERITING(nsBoxFrame)

nsSliderFrame::nsSliderFrame(ComputedStyle* aStyle, nsPresContext* aPresContext)
    : nsBoxFrame(aStyle, aPresContext, kClassID),
      mRatio(0.0f),
      mDragStart(0),
      mThumbStart(0),
      mCurPos(0),
      mChange(0),
      mDragFinished(true),
      mUserChanged(false),
      mScrollingWithAPZ(false),
      mSuppressionActive(false) {}

// stop timer
nsSliderFrame::~nsSliderFrame() {
  if (mSuppressionActive) {
    if (nsIPresShell* shell = PresShell()) {
      shell->SuppressDisplayport(false);
    }
  }
}

void nsSliderFrame::Init(nsIContent* aContent, nsContainerFrame* aParent,
                         nsIFrame* aPrevInFlow) {
  nsBoxFrame::Init(aContent, aParent, aPrevInFlow);

  static bool gotPrefs = false;
  if (!gotPrefs) {
    gotPrefs = true;

    gMiddlePref = Preferences::GetBool("middlemouse.scrollbarPosition");
    gSnapMultiplier = Preferences::GetInt("slider.snapMultiplier");
  }

  mCurPos = GetCurrentPosition(aContent);
}

void nsSliderFrame::RemoveFrame(ChildListID aListID, nsIFrame* aOldFrame) {
  nsBoxFrame::RemoveFrame(aListID, aOldFrame);
  if (mFrames.IsEmpty()) RemoveListener();
}

void nsSliderFrame::InsertFrames(ChildListID aListID, nsIFrame* aPrevFrame,
                                 nsFrameList& aFrameList) {
  bool wasEmpty = mFrames.IsEmpty();
  nsBoxFrame::InsertFrames(aListID, aPrevFrame, aFrameList);
  if (wasEmpty) AddListener();
}

void nsSliderFrame::AppendFrames(ChildListID aListID, nsFrameList& aFrameList) {
  // if we have no children and on was added then make sure we add the
  // listener
  bool wasEmpty = mFrames.IsEmpty();
  nsBoxFrame::AppendFrames(aListID, aFrameList);
  if (wasEmpty) AddListener();
}

int32_t nsSliderFrame::GetCurrentPosition(nsIContent* content) {
  return GetIntegerAttribute(content, nsGkAtoms::curpos, 0);
}

int32_t nsSliderFrame::GetMinPosition(nsIContent* content) {
  return GetIntegerAttribute(content, nsGkAtoms::minpos, 0);
}

int32_t nsSliderFrame::GetMaxPosition(nsIContent* content) {
  return GetIntegerAttribute(content, nsGkAtoms::maxpos, 100);
}

int32_t nsSliderFrame::GetIncrement(nsIContent* content) {
  return GetIntegerAttribute(content, nsGkAtoms::increment, 1);
}

int32_t nsSliderFrame::GetPageIncrement(nsIContent* content) {
  return GetIntegerAttribute(content, nsGkAtoms::pageincrement, 10);
}

int32_t nsSliderFrame::GetIntegerAttribute(nsIContent* content, nsAtom* atom,
                                           int32_t defaultValue) {
  nsAutoString value;
  if (content->IsElement()) {
    content->AsElement()->GetAttr(kNameSpaceID_None, atom, value);
  }
  if (!value.IsEmpty()) {
    nsresult error;

    // convert it to an integer
    defaultValue = value.ToInteger(&error);
  }

  return defaultValue;
}

nsresult nsSliderFrame::AttributeChanged(int32_t aNameSpaceID,
                                         nsAtom* aAttribute, int32_t aModType) {
  nsresult rv =
      nsBoxFrame::AttributeChanged(aNameSpaceID, aAttribute, aModType);
  // if the current position changes
  if (aAttribute == nsGkAtoms::curpos) {
    CurrentPositionChanged();
  } else if (aAttribute == nsGkAtoms::minpos ||
             aAttribute == nsGkAtoms::maxpos) {
    // bounds check it.

    nsIFrame* scrollbarBox = GetScrollbar();
    nsCOMPtr<nsIContent> scrollbar = GetContentOfBox(scrollbarBox);
    int32_t current = GetCurrentPosition(scrollbar);
    int32_t min = GetMinPosition(scrollbar);
    int32_t max = GetMaxPosition(scrollbar);

    if (current < min || current > max) {
      int32_t direction = 0;
      if (current < min || max < min) {
        current = min;
        direction = -1;
      } else if (current > max) {
        current = max;
        direction = 1;
      }

      // set the new position and notify observers
      nsScrollbarFrame* scrollbarFrame = do_QueryFrame(scrollbarBox);
      if (scrollbarFrame) {
        nsIScrollbarMediator* mediator = scrollbarFrame->GetScrollbarMediator();
        scrollbarFrame->SetIncrementToWhole(direction);
        if (mediator) {
          mediator->ScrollByWhole(scrollbarFrame, direction,
                                  nsIScrollbarMediator::ENABLE_SNAP);
        }
      }
      // 'this' might be destroyed here

      nsContentUtils::AddScriptRunner(new nsSetAttrRunnable(
          scrollbar->AsElement(), nsGkAtoms::curpos, current));
    }
  }

  if (aAttribute == nsGkAtoms::minpos || aAttribute == nsGkAtoms::maxpos ||
      aAttribute == nsGkAtoms::pageincrement ||
      aAttribute == nsGkAtoms::increment) {
    PresShell()->FrameNeedsReflow(this, nsIPresShell::eStyleChange,
                                  NS_FRAME_IS_DIRTY);
  }

  return rv;
}

void nsSliderFrame::BuildDisplayList(nsDisplayListBuilder* aBuilder,
                                     const nsDisplayListSet& aLists) {
  if (aBuilder->IsForEventDelivery() && isDraggingThumb()) {
    // This is EVIL, we shouldn't be messing with event delivery just to get
    // thumb mouse drag events to arrive at the slider!
    aLists.Outlines()->AppendToTop(
        MakeDisplayItem<nsDisplayEventReceiver>(aBuilder, this));
    return;
  }

  nsBoxFrame::BuildDisplayList(aBuilder, aLists);
}

static bool UsesCustomScrollbarMediator(nsIFrame* scrollbarBox) {
  if (nsScrollbarFrame* scrollbarFrame = do_QueryFrame(scrollbarBox)) {
    if (nsIScrollbarMediator* mediator =
            scrollbarFrame->GetScrollbarMediator()) {
      nsIScrollableFrame* scrollFrame = do_QueryFrame(mediator);
      // The scrollbar mediator is not the scroll frame.
      // That means this scroll frame has a custom scrollbar mediator.
      if (!scrollFrame) {
        return true;
      }
    }
  }
  return false;
}

void nsSliderFrame::BuildDisplayListForChildren(
    nsDisplayListBuilder* aBuilder, const nsDisplayListSet& aLists) {
  // if we are too small to have a thumb don't paint it.
  nsIFrame* thumb = nsBox::GetChildXULBox(this);

  if (thumb) {
    nsRect thumbRect(thumb->GetRect());
    nsMargin m;
    thumb->GetXULMargin(m);
    thumbRect.Inflate(m);

    nsRect sliderTrack;
    GetXULClientRect(sliderTrack);

    if (sliderTrack.width < thumbRect.width ||
        sliderTrack.height < thumbRect.height)
      return;

    // If this scrollbar is the scrollbar of an actively scrolled scroll frame,
    // layerize the scrollbar thumb, wrap it in its own ContainerLayer and
    // attach scrolling information to it.
    // We do this here and not in the thumb's nsBoxFrame::BuildDisplayList so
    // that the event region that gets created for the thumb is included in
    // the nsDisplayOwnLayer contents.

    const mozilla::layers::ScrollableLayerGuid::ViewID scrollTargetId =
        aBuilder->GetCurrentScrollbarTarget();
    const bool thumbGetsLayer =
        (scrollTargetId != layers::ScrollableLayerGuid::NULL_SCROLL_ID);

    if (thumbGetsLayer) {
      const Maybe<ScrollDirection> scrollDirection =
          aBuilder->GetCurrentScrollbarDirection();
      MOZ_ASSERT(scrollDirection.isSome());
      const bool isHorizontal =
          *scrollDirection == ScrollDirection::eHorizontal;
      const float appUnitsPerCss = float(AppUnitsPerCSSPixel());
      const CSSCoord thumbLength = NSAppUnitsToFloatPixels(
          isHorizontal ? thumbRect.width : thumbRect.height, appUnitsPerCss);

      nsIFrame* scrollbarBox = GetScrollbar();
      bool isAsyncDraggable = !UsesCustomScrollbarMediator(scrollbarBox);

      nsPoint scrollPortOrigin;
      if (nsIScrollableFrame* scrollFrame =
              do_QueryFrame(scrollbarBox->GetParent())) {
        scrollPortOrigin = scrollFrame->GetScrollPortRect().TopLeft();
      } else {
        isAsyncDraggable = false;
      }

      // This rect is the range in which the scroll thumb can slide in.
      sliderTrack = sliderTrack + GetRect().TopLeft() +
                    scrollbarBox->GetPosition() - scrollPortOrigin;
      const CSSCoord sliderTrackStart = NSAppUnitsToFloatPixels(
          isHorizontal ? sliderTrack.x : sliderTrack.y, appUnitsPerCss);
      const CSSCoord sliderTrackLength = NSAppUnitsToFloatPixels(
          isHorizontal ? sliderTrack.width : sliderTrack.height,
          appUnitsPerCss);
      const CSSCoord thumbStart = NSAppUnitsToFloatPixels(
          isHorizontal ? thumbRect.x : thumbRect.y, appUnitsPerCss);

      const nsRect overflow = thumb->GetVisualOverflowRectRelativeToParent();
      nsSize refSize = aBuilder->RootReferenceFrame()->GetSize();
      const gfxSize scale = nsLayoutUtils::GetTransformToAncestorScale(thumb);
      if (scale.width != 0 && scale.height != 0) {
        refSize.width /= scale.width;
        refSize.height /= scale.height;
      }
      nsRect dirty = aBuilder->GetVisibleRect().Intersect(thumbRect);
      dirty = nsLayoutUtils::ComputePartialPrerenderArea(
          aBuilder->GetVisibleRect(), overflow, refSize);

      nsDisplayListBuilder::AutoBuildingDisplayList buildingDisplayList(
          aBuilder, this, dirty, dirty);

      // Clip the thumb layer to the slider track. This is necessary to ensure
      // FrameLayerBuilder is able to merge content before and after the
      // scrollframe into the same layer (otherwise it thinks the thumb could
      // potentially move anywhere within the existing clip).
      DisplayListClipState::AutoSaveRestore thumbClipState(aBuilder);
      thumbClipState.ClipContainingBlockDescendants(
          GetRectRelativeToSelf() + aBuilder->ToReferenceFrame(this));

      // Have the thumb's container layer capture the current clip, so
      // it doesn't apply to the thumb's contents. This allows the contents
      // to be fully rendered even if they're partially or fully offscreen,
      // so async scrolling can still bring it into view.
      DisplayListClipState::AutoSaveRestore thumbContentsClipState(aBuilder);
      thumbContentsClipState.Clear();

      nsDisplayListBuilder::AutoContainerASRTracker contASRTracker(aBuilder);
      nsDisplayListCollection tempLists(aBuilder);
      nsBoxFrame::BuildDisplayListForChildren(aBuilder, tempLists);

      // This is a bit of a hack. Collect up all descendant display items
      // and merge them into a single Content() list.
      nsDisplayList masterList;
      masterList.AppendToTop(tempLists.BorderBackground());
      masterList.AppendToTop(tempLists.BlockBorderBackgrounds());
      masterList.AppendToTop(tempLists.Floats());
      masterList.AppendToTop(tempLists.Content());
      masterList.AppendToTop(tempLists.PositionedDescendants());
      masterList.AppendToTop(tempLists.Outlines());

      // Restore the saved clip so it applies to the thumb container layer.
      thumbContentsClipState.Restore();

      // Wrap the list to make it its own layer.
      const ActiveScrolledRoot* ownLayerASR = contASRTracker.GetContainerASR();
      aLists.Content()->AppendToTop(MakeDisplayItem<nsDisplayOwnLayer>(
          aBuilder, this, &masterList, ownLayerASR,
          nsDisplayOwnLayerFlags::eNone,
          ScrollbarData::CreateForThumb(*scrollDirection, GetThumbRatio(),
                                        thumbStart, thumbLength,
                                        isAsyncDraggable, sliderTrackStart,
                                        sliderTrackLength, scrollTargetId)));

      return;
    }
  }

  nsBoxFrame::BuildDisplayListForChildren(aBuilder, aLists);
}

NS_IMETHODIMP
nsSliderFrame::DoXULLayout(nsBoxLayoutState& aState) {
  // get the thumb should be our only child
  nsIFrame* thumbBox = nsBox::GetChildXULBox(this);

  if (!thumbBox) {
    SyncLayout(aState);
    return NS_OK;
  }

  EnsureOrient();

  // get the content area inside our borders
  nsRect clientRect;
  GetXULClientRect(clientRect);

  // get the scrollbar
  nsIFrame* scrollbarBox = GetScrollbar();
  nsCOMPtr<nsIContent> scrollbar = GetContentOfBox(scrollbarBox);

  // get the thumb's pref size
  nsSize thumbSize = thumbBox->GetXULPrefSize(aState);

  if (IsXULHorizontal())
    thumbSize.height = clientRect.height;
  else
    thumbSize.width = clientRect.width;

  int32_t curPos = GetCurrentPosition(scrollbar);
  int32_t minPos = GetMinPosition(scrollbar);
  int32_t maxPos = GetMaxPosition(scrollbar);
  int32_t pageIncrement = GetPageIncrement(scrollbar);

  maxPos = std::max(minPos, maxPos);
  curPos = clamped(curPos, minPos, maxPos);

  nscoord& availableLength =
      IsXULHorizontal() ? clientRect.width : clientRect.height;
  nscoord& thumbLength = IsXULHorizontal() ? thumbSize.width : thumbSize.height;

  if ((pageIncrement + maxPos - minPos) > 0 && thumbBox->GetXULFlex() > 0) {
    float ratio = float(pageIncrement) / float(maxPos - minPos + pageIncrement);
    thumbLength =
        std::max(thumbLength, NSToCoordRound(availableLength * ratio));
  }

  // Round the thumb's length to device pixels.
  nsPresContext* presContext = PresContext();
  thumbLength = presContext->DevPixelsToAppUnits(
      presContext->AppUnitsToDevPixels(thumbLength));

  // mRatio translates the thumb position in app units to the value.
  mRatio = (minPos != maxPos)
               ? float(availableLength - thumbLength) / float(maxPos - minPos)
               : 1;

  // in reverse mode, curpos is reversed such that lower values are to the
  // right or bottom and increase leftwards or upwards. In this case, use the
  // offset from the end instead of the beginning.
  bool reverse = mContent->AsElement()->AttrValueIs(
      kNameSpaceID_None, nsGkAtoms::dir, nsGkAtoms::reverse, eCaseMatters);
  nscoord pos = reverse ? (maxPos - curPos) : (curPos - minPos);

  // set the thumb's coord to be the current pos * the ratio.
  nsRect thumbRect(clientRect.x, clientRect.y, thumbSize.width,
                   thumbSize.height);
  int32_t& thumbPos = (IsXULHorizontal() ? thumbRect.x : thumbRect.y);
  thumbPos += NSToCoordRound(pos * mRatio);

  nsRect oldThumbRect(thumbBox->GetRect());
  LayoutChildAt(aState, thumbBox, thumbRect);

  SyncLayout(aState);

  // Redraw only if thumb changed size.
  if (!oldThumbRect.IsEqualInterior(thumbRect)) XULRedraw(aState);

  return NS_OK;
}

nsresult nsSliderFrame::HandleEvent(nsPresContext* aPresContext,
                                    WidgetGUIEvent* aEvent,
                                    nsEventStatus* aEventStatus) {
  NS_ENSURE_ARG_POINTER(aEventStatus);

  if (mAPZDragInitiated &&
      *mAPZDragInitiated == InputAPZContext::GetInputBlockId() &&
      aEvent->mMessage == eMouseDown) {
    // If we get the mousedown after the APZ notification, then immediately
    // switch into the state corresponding to an APZ thumb-drag. Note that
    // we can't just do this in AsyncScrollbarDragInitiated() directly because
    // the handling for this mousedown event in the presShell will reset the
    // capturing content which makes isDraggingThumb() return false. We check
    // the input block here to make sure that we correctly handle any ordering
    // of {eMouseDown arriving, AsyncScrollbarDragInitiated() being called}.
    mAPZDragInitiated = Nothing();
    DragThumb(true);
    mScrollingWithAPZ = true;
    return NS_OK;
  }

  // If a web page calls event.preventDefault() we still want to
  // scroll when scroll arrow is clicked. See bug 511075.
  if (!mContent->IsInNativeAnonymousSubtree() &&
      nsEventStatus_eConsumeNoDefault == *aEventStatus) {
    return NS_OK;
  }

  if (!mDragFinished && !isDraggingThumb()) {
    StopDrag();
    return NS_OK;
  }

  nsIFrame* scrollbarBox = GetScrollbar();
  nsCOMPtr<nsIContent> scrollbar;
  scrollbar = GetContentOfBox(scrollbarBox);
  bool isHorizontal = IsXULHorizontal();

  if (isDraggingThumb()) {
    switch (aEvent->mMessage) {
      case eTouchMove:
      case eMouseMove: {
        if (mScrollingWithAPZ) {
          break;
        }
        nsPoint eventPoint;
        if (!GetEventPoint(aEvent, eventPoint)) {
          break;
        }
        if (mChange) {
          // On Linux the destination point is determined by the initial click
          // on the scrollbar track and doesn't change until the mouse button
          // is released.
#ifndef MOZ_WIDGET_GTK
          // On the other platforms we need to update the destination point now.
          mDestinationPoint = eventPoint;
          StopRepeat();
          StartRepeat();
#endif
          break;
        }

        nscoord pos = isHorizontal ? eventPoint.x : eventPoint.y;

        nsIFrame* thumbFrame = mFrames.FirstChild();
        if (!thumbFrame) {
          return NS_OK;
        }

        // take our current position and subtract the start location
        pos -= mDragStart;
        bool isMouseOutsideThumb = false;
        if (gSnapMultiplier) {
          nsSize thumbSize = thumbFrame->GetSize();
          if (isHorizontal) {
            // horizontal scrollbar - check if mouse is above or below thumb
            // XXXbz what about looking at the .y of the thumb's rect?  Is that
            // always zero here?
            if (eventPoint.y < -gSnapMultiplier * thumbSize.height ||
                eventPoint.y >
                    thumbSize.height + gSnapMultiplier * thumbSize.height)
              isMouseOutsideThumb = true;
          } else {
            // vertical scrollbar - check if mouse is left or right of thumb
            if (eventPoint.x < -gSnapMultiplier * thumbSize.width ||
                eventPoint.x >
                    thumbSize.width + gSnapMultiplier * thumbSize.width)
              isMouseOutsideThumb = true;
          }
        }
        if (aEvent->mClass == eTouchEventClass) {
          *aEventStatus = nsEventStatus_eConsumeNoDefault;
        }
        if (isMouseOutsideThumb) {
          SetCurrentThumbPosition(scrollbar, mThumbStart, false, false);
          return NS_OK;
        }

        // set it
        SetCurrentThumbPosition(scrollbar, pos, false, true);  // with snapping
      } break;

      case eTouchEnd:
      case eMouseUp:
        if (ShouldScrollForEvent(aEvent)) {
          StopDrag();
          // we MUST call nsFrame HandleEvent for mouse ups to maintain the
          // selection state and capture state.
          return nsFrame::HandleEvent(aPresContext, aEvent, aEventStatus);
        }
        break;

      default:
        break;
    }

    // return nsFrame::HandleEvent(aPresContext, aEvent, aEventStatus);
    return NS_OK;
  } else if (ShouldScrollToClickForEvent(aEvent)) {
    nsPoint eventPoint;
    if (!GetEventPoint(aEvent, eventPoint)) {
      return NS_OK;
    }
    nscoord pos = isHorizontal ? eventPoint.x : eventPoint.y;

    // adjust so that the middle of the thumb is placed under the click
    nsIFrame* thumbFrame = mFrames.FirstChild();
    if (!thumbFrame) {
      return NS_OK;
    }
    nsSize thumbSize = thumbFrame->GetSize();
    nscoord thumbLength = isHorizontal ? thumbSize.width : thumbSize.height;

    // set it
    AutoWeakFrame weakFrame(this);
    // should aMaySnap be true here?
    SetCurrentThumbPosition(scrollbar, pos - thumbLength / 2, false, false);
    NS_ENSURE_TRUE(weakFrame.IsAlive(), NS_OK);

    DragThumb(true);

#ifdef MOZ_WIDGET_GTK
    RefPtr<Element> thumb = thumbFrame->GetContent()->AsElement();
    thumb->SetAttr(kNameSpaceID_None, nsGkAtoms::active,
                   NS_LITERAL_STRING("true"), true);
#endif

    if (aEvent->mClass == eTouchEventClass) {
      *aEventStatus = nsEventStatus_eConsumeNoDefault;
    }

    if (isHorizontal)
      mThumbStart = thumbFrame->GetPosition().x;
    else
      mThumbStart = thumbFrame->GetPosition().y;

    mDragStart = pos - mThumbStart;
  }
#ifdef MOZ_WIDGET_GTK
  else if (ShouldScrollForEvent(aEvent) && aEvent->mClass == eMouseEventClass &&
           aEvent->AsMouseEvent()->button == WidgetMouseEvent::eRightButton) {
    // HandlePress and HandleRelease are usually called via
    // nsFrame::HandleEvent, but only for the left mouse button.
    if (aEvent->mMessage == eMouseDown) {
      HandlePress(aPresContext, aEvent, aEventStatus);
    } else if (aEvent->mMessage == eMouseUp) {
      HandleRelease(aPresContext, aEvent, aEventStatus);
    }

    return NS_OK;
  }
#endif

  // XXX hack until handle release is actually called in nsframe.
  //  if (aEvent->mMessage == eMouseOut ||
  //      aEvent->mMessage == NS_MOUSE_RIGHT_BUTTON_UP ||
  //      aEvent->mMessage == NS_MOUSE_LEFT_BUTTON_UP) {
  //    HandleRelease(aPresContext, aEvent, aEventStatus);
  //  }

  if (aEvent->mMessage == eMouseOut && mChange)
    HandleRelease(aPresContext, aEvent, aEventStatus);

  return nsFrame::HandleEvent(aPresContext, aEvent, aEventStatus);
}

// Helper function to collect the "scroll to click" metric. Beware of
// caching this, users expect to be able to change the system preference
// and see the browser change its behavior immediately.
bool nsSliderFrame::GetScrollToClick() {
  if (GetScrollbar() != this) {
    return LookAndFeel::GetInt(LookAndFeel::eIntID_ScrollToClick, false);
  }

  if (mContent->AsElement()->AttrValueIs(kNameSpaceID_None,
                                         nsGkAtoms::movetoclick,
                                         nsGkAtoms::_true, eCaseMatters)) {
    return true;
  }
  if (mContent->AsElement()->AttrValueIs(kNameSpaceID_None,
                                         nsGkAtoms::movetoclick,
                                         nsGkAtoms::_false, eCaseMatters)) {
    return false;
  }

#ifdef XP_MACOSX
  return true;
#else
  return false;
#endif
}

nsIFrame* nsSliderFrame::GetScrollbar() {
  // if we are in a scrollbar then return the scrollbar's content node
  // if we are not then return ours.
  nsIFrame* scrollbar;
  nsScrollbarButtonFrame::GetParentWithTag(nsGkAtoms::scrollbar, this,
                                           scrollbar);

  if (scrollbar == nullptr) return this;

  return scrollbar->IsXULBoxFrame() ? scrollbar : this;
}

void nsSliderFrame::PageUpDown(nscoord change) {
  // on a page up or down get our page increment. We get this by getting the
  // scrollbar we are in and asking it for the current position and the page
  // increment. If we are not in a scrollbar we will get the values from our own
  // node.
  nsIFrame* scrollbarBox = GetScrollbar();
  nsCOMPtr<nsIContent> scrollbar;
  scrollbar = GetContentOfBox(scrollbarBox);

  nscoord pageIncrement = GetPageIncrement(scrollbar);
  int32_t curpos = GetCurrentPosition(scrollbar);
  int32_t minpos = GetMinPosition(scrollbar);
  int32_t maxpos = GetMaxPosition(scrollbar);

  // get the new position and make sure it is in bounds
  int32_t newpos = curpos + change * pageIncrement;
  if (newpos < minpos || maxpos < minpos)
    newpos = minpos;
  else if (newpos > maxpos)
    newpos = maxpos;

  SetCurrentPositionInternal(scrollbar, newpos, true);
}

// called when the current position changed and we need to update the thumb's
// location
void nsSliderFrame::CurrentPositionChanged() {
  nsIFrame* scrollbarBox = GetScrollbar();
  nsCOMPtr<nsIContent> scrollbar = GetContentOfBox(scrollbarBox);

  // get the current position
  int32_t curPos = GetCurrentPosition(scrollbar);

  // do nothing if the position did not change
  if (mCurPos == curPos) return;

  // get our current min and max position from our content node
  int32_t minPos = GetMinPosition(scrollbar);
  int32_t maxPos = GetMaxPosition(scrollbar);

  maxPos = std::max(minPos, maxPos);
  curPos = clamped(curPos, minPos, maxPos);

  // get the thumb's rect
  nsIFrame* thumbFrame = mFrames.FirstChild();
  if (!thumbFrame) return;  // The thumb may stream in asynchronously via XBL.

  nsRect thumbRect = thumbFrame->GetRect();

  nsRect clientRect;
  GetXULClientRect(clientRect);

  // figure out the new rect
  nsRect newThumbRect(thumbRect);

  bool reverse = mContent->AsElement()->AttrValueIs(
      kNameSpaceID_None, nsGkAtoms::dir, nsGkAtoms::reverse, eCaseMatters);
  nscoord pos = reverse ? (maxPos - curPos) : (curPos - minPos);

  if (IsXULHorizontal())
    newThumbRect.x = clientRect.x + NSToCoordRound(pos * mRatio);
  else
    newThumbRect.y = clientRect.y + NSToCoordRound(pos * mRatio);

  // avoid putting the scroll thumb at subpixel positions which cause needless
  // invalidations
  nscoord appUnitsPerPixel = PresContext()->AppUnitsPerDevPixel();
  nsPoint snappedThumbLocation =
      ToAppUnits(newThumbRect.TopLeft().ToNearestPixels(appUnitsPerPixel),
                 appUnitsPerPixel);
  if (IsXULHorizontal()) {
    newThumbRect.x = snappedThumbLocation.x;
  } else {
    newThumbRect.y = snappedThumbLocation.y;
  }

  // set the rect
  thumbFrame->SetRect(newThumbRect);

  // Request a repaint of the scrollbar
  nsScrollbarFrame* scrollbarFrame = do_QueryFrame(scrollbarBox);
  nsIScrollbarMediator* mediator =
      scrollbarFrame ? scrollbarFrame->GetScrollbarMediator() : nullptr;
  if (!mediator || !mediator->ShouldSuppressScrollbarRepaints()) {
    SchedulePaint();
  }

  mCurPos = curPos;
}

static void UpdateAttribute(Element* aScrollbar, nscoord aNewPos, bool aNotify,
                            bool aIsSmooth) {
  nsAutoString str;
  str.AppendInt(aNewPos);

  if (aIsSmooth) {
    aScrollbar->SetAttr(kNameSpaceID_None, nsGkAtoms::smooth,
                        NS_LITERAL_STRING("true"), false);
  }
  aScrollbar->SetAttr(kNameSpaceID_None, nsGkAtoms::curpos, str, aNotify);
  if (aIsSmooth) {
    aScrollbar->UnsetAttr(kNameSpaceID_None, nsGkAtoms::smooth, false);
  }
}

// Use this function when you want to set the scroll position via the position
// of the scrollbar thumb, e.g. when dragging the slider. This function scrolls
// the content in such a way that thumbRect.x/.y becomes aNewThumbPos.
void nsSliderFrame::SetCurrentThumbPosition(nsIContent* aScrollbar,
                                            nscoord aNewThumbPos,
                                            bool aIsSmooth, bool aMaySnap) {
  nsRect crect;
  GetXULClientRect(crect);
  nscoord offset = IsXULHorizontal() ? crect.x : crect.y;
  int32_t newPos = NSToIntRound((aNewThumbPos - offset) / mRatio);

  if (aMaySnap &&
      mContent->AsElement()->AttrValueIs(kNameSpaceID_None, nsGkAtoms::snap,
                                         nsGkAtoms::_true, eCaseMatters)) {
    // If snap="true", then the slider may only be set to min + (increment * x).
    // Otherwise, the slider may be set to any positive integer.
    int32_t increment = GetIncrement(aScrollbar);
    newPos = NSToIntRound(newPos / float(increment)) * increment;
  }

  SetCurrentPosition(aScrollbar, newPos, aIsSmooth);
}

// Use this function when you know the target scroll position of the scrolled
// content. aNewPos should be passed to this function as a position as if the
// minpos is 0. That is, the minpos will be added to the position by this
// function. In a reverse direction slider, the newpos should be the distance
// from the end.
void nsSliderFrame::SetCurrentPosition(nsIContent* aScrollbar, int32_t aNewPos,
                                       bool aIsSmooth) {
  // get min and max position from our content node
  int32_t minpos = GetMinPosition(aScrollbar);
  int32_t maxpos = GetMaxPosition(aScrollbar);

  // in reverse direction sliders, flip the value so that it goes from
  // right to left, or bottom to top.
  if (mContent->AsElement()->AttrValueIs(kNameSpaceID_None, nsGkAtoms::dir,
                                         nsGkAtoms::reverse, eCaseMatters))
    aNewPos = maxpos - aNewPos;
  else
    aNewPos += minpos;

  // get the new position and make sure it is in bounds
  if (aNewPos < minpos || maxpos < minpos)
    aNewPos = minpos;
  else if (aNewPos > maxpos)
    aNewPos = maxpos;

  SetCurrentPositionInternal(aScrollbar, aNewPos, aIsSmooth);
}

void nsSliderFrame::SetCurrentPositionInternal(nsIContent* aScrollbar,
                                               int32_t aNewPos,
                                               bool aIsSmooth) {
  nsCOMPtr<nsIContent> scrollbar = aScrollbar;
  nsIFrame* scrollbarBox = GetScrollbar();
  AutoWeakFrame weakFrame(this);

  mUserChanged = true;

  nsScrollbarFrame* scrollbarFrame = do_QueryFrame(scrollbarBox);
  if (scrollbarFrame) {
    // See if we have a mediator.
    nsIScrollbarMediator* mediator = scrollbarFrame->GetScrollbarMediator();
    if (mediator) {
      nscoord oldPos =
          nsPresContext::CSSPixelsToAppUnits(GetCurrentPosition(scrollbar));
      nscoord newPos = nsPresContext::CSSPixelsToAppUnits(aNewPos);
      mediator->ThumbMoved(scrollbarFrame, oldPos, newPos);
      if (!weakFrame.IsAlive()) {
        return;
      }
      UpdateAttribute(scrollbar->AsElement(), aNewPos, /* aNotify */ false,
                      aIsSmooth);
      CurrentPositionChanged();
      mUserChanged = false;
      return;
    }
  }

  UpdateAttribute(scrollbar->AsElement(), aNewPos, true, aIsSmooth);
  if (!weakFrame.IsAlive()) {
    return;
  }
  mUserChanged = false;

#ifdef DEBUG_SLIDER
  printf("Current Pos=%d\n", aNewPos);
#endif
}

void nsSliderFrame::SetInitialChildList(ChildListID aListID,
                                        nsFrameList& aChildList) {
  nsBoxFrame::SetInitialChildList(aListID, aChildList);
  if (aListID == kPrincipalList) {
    AddListener();
  }
}

nsresult nsSliderMediator::HandleEvent(dom::Event* aEvent) {
  // Only process the event if the thumb is not being dragged.
  if (mSlider && !mSlider->isDraggingThumb()) return mSlider->StartDrag(aEvent);

  return NS_OK;
}

class AsyncScrollbarDragStarter final : public nsAPostRefreshObserver {
 public:
  AsyncScrollbarDragStarter(nsIPresShell* aPresShell, nsIWidget* aWidget,
                            const AsyncDragMetrics& aDragMetrics)
      : mPresShell(aPresShell), mWidget(aWidget), mDragMetrics(aDragMetrics) {}
  virtual ~AsyncScrollbarDragStarter() {}

  void DidRefresh() override {
    if (!mPresShell) {
      MOZ_ASSERT_UNREACHABLE(
          "Post-refresh observer fired again after failed attempt at "
          "unregistering it");
      return;
    }

    mWidget->StartAsyncScrollbarDrag(mDragMetrics);

    if (!mPresShell->RemovePostRefreshObserver(this)) {
      MOZ_ASSERT_UNREACHABLE(
          "Unable to unregister post-refresh observer! Leaking it instead of "
          "leaving garbage registered");
      // Graceful handling, just in case...
      mPresShell = nullptr;
      mWidget = nullptr;
      return;
    }

    delete this;
  }

 private:
  RefPtr<nsIPresShell> mPresShell;
  RefPtr<nsIWidget> mWidget;
  AsyncDragMetrics mDragMetrics;
};

static bool UsesSVGEffects(nsIFrame* aFrame) {
  return aFrame->StyleEffects()->HasFilters() ||
         nsSVGIntegrationUtils::UsingMaskOrClipPathForFrame(aFrame);
}

static bool ScrollFrameWillBuildScrollInfoLayer(nsIFrame* aScrollFrame) {
  if (gfx::gfxVars::UseWebRender()) {
    // If WebRender is enabled, even scrollframes enclosed in SVG effects can
    // be drag-scrolled by APZ.
    return false;
  }
  nsIFrame* current = aScrollFrame;
  while (current) {
    if (UsesSVGEffects(current)) {
      return true;
    }
    current = nsLayoutUtils::GetParentOrPlaceholderForCrossDoc(current);
  }
  return false;
}

nsIScrollableFrame* nsSliderFrame::GetScrollFrame() {
  nsIFrame* scrollbarBox = GetScrollbar();
  if (!scrollbarBox) {
    return nullptr;
  }

  nsContainerFrame* scrollFrame = scrollbarBox->GetParent();
  if (!scrollFrame) {
    return nullptr;
  }

  nsIScrollableFrame* scrollFrameAsScrollable = do_QueryFrame(scrollFrame);
  return scrollFrameAsScrollable;
}

void nsSliderFrame::StartAPZDrag(WidgetGUIEvent* aEvent) {
  if (!aEvent->mFlags.mHandledByAPZ) {
    return;
  }

  if (!gfxPlatform::GetPlatform()->SupportsApzDragInput()) {
    return;
  }

  nsIFrame* scrollbarBox = GetScrollbar();
  nsContainerFrame* scrollFrame = scrollbarBox->GetParent();
  if (!scrollFrame) {
    return;
  }

  nsIContent* scrollableContent = scrollFrame->GetContent();
  if (!scrollableContent) {
    return;
  }

  // APZ dragging requires the scrollbar to be layerized, which doesn't
  // happen for scroll info layers.
  if (ScrollFrameWillBuildScrollInfoLayer(scrollFrame)) {
    return;
  }

  // Custom scrollbar mediators are not supported in the APZ codepath.
  if (UsesCustomScrollbarMediator(scrollbarBox)) {
    return;
  }

  bool isHorizontal = IsXULHorizontal();

  mozilla::layers::ScrollableLayerGuid::ViewID scrollTargetId;
  bool hasID = nsLayoutUtils::FindIDFor(scrollableContent, &scrollTargetId);
  bool hasAPZView =
      hasID && (scrollTargetId != layers::ScrollableLayerGuid::NULL_SCROLL_ID);

  if (!hasAPZView) {
    return;
  }

  if (!nsLayoutUtils::HasDisplayPort(scrollableContent)) {
    return;
  }

  nsIPresShell* shell = PresShell();
  uint64_t inputblockId = InputAPZContext::GetInputBlockId();
  uint32_t presShellId = shell->GetPresShellId();
  AsyncDragMetrics dragMetrics(
      scrollTargetId, presShellId, inputblockId,
      NSAppUnitsToFloatPixels(mDragStart, float(AppUnitsPerCSSPixel())),
      isHorizontal ? ScrollDirection::eHorizontal : ScrollDirection::eVertical);

  // It's important to set this before calling
  // nsIWidget::StartAsyncScrollbarDrag(), because in some configurations, that
  // can call AsyncScrollbarDragRejected() synchronously, which clears the flag
  // (and we want it to stay cleared in that case).
  mScrollingWithAPZ = true;

  // When we start an APZ drag, we wont get mouse events for the drag.
  // APZ will consume them all and only notify us of the new scroll position.
  bool waitForRefresh = InputAPZContext::HavePendingLayerization();
  nsIWidget* widget = this->GetNearestWidget();
  if (waitForRefresh) {
    waitForRefresh = shell->AddPostRefreshObserver(
        new AsyncScrollbarDragStarter(shell, widget, dragMetrics));
  }
  if (!waitForRefresh) {
    widget->StartAsyncScrollbarDrag(dragMetrics);
  }
}

nsresult nsSliderFrame::StartDrag(Event* aEvent) {
#ifdef DEBUG_SLIDER
  printf("Begin dragging\n");
#endif
  if (mContent->AsElement()->AttrValueIs(kNameSpaceID_None, nsGkAtoms::disabled,
                                         nsGkAtoms::_true, eCaseMatters))
    return NS_OK;

  WidgetGUIEvent* event = aEvent->WidgetEventPtr()->AsGUIEvent();

  if (!ShouldScrollForEvent(event)) {
    return NS_OK;
  }

  nsPoint pt;
  if (!GetEventPoint(event, pt)) {
    return NS_OK;
  }
  bool isHorizontal = IsXULHorizontal();
  nscoord pos = isHorizontal ? pt.x : pt.y;

  // If we should scroll-to-click, first place the middle of the slider thumb
  // under the mouse.
  nsCOMPtr<nsIContent> scrollbar;
  nscoord newpos = pos;
  bool scrollToClick = ShouldScrollToClickForEvent(event);
  if (scrollToClick) {
    // adjust so that the middle of the thumb is placed under the click
    nsIFrame* thumbFrame = mFrames.FirstChild();
    if (!thumbFrame) {
      return NS_OK;
    }
    nsSize thumbSize = thumbFrame->GetSize();
    nscoord thumbLength = isHorizontal ? thumbSize.width : thumbSize.height;

    newpos -= (thumbLength / 2);

    nsIFrame* scrollbarBox = GetScrollbar();
    scrollbar = GetContentOfBox(scrollbarBox);
  }

  DragThumb(true);

  if (scrollToClick) {
    // should aMaySnap be true here?
    SetCurrentThumbPosition(scrollbar, newpos, false, false);
  }

  nsIFrame* thumbFrame = mFrames.FirstChild();
  if (!thumbFrame) {
    return NS_OK;
  }

#ifdef MOZ_WIDGET_GTK
  RefPtr<Element> thumb = thumbFrame->GetContent()->AsElement();
  thumb->SetAttr(kNameSpaceID_None, nsGkAtoms::active,
                 NS_LITERAL_STRING("true"), true);
#endif

  if (isHorizontal)
    mThumbStart = thumbFrame->GetPosition().x;
  else
    mThumbStart = thumbFrame->GetPosition().y;

  mDragStart = pos - mThumbStart;

  mScrollingWithAPZ = false;
  StartAPZDrag(event);  // sets mScrollingWithAPZ=true if appropriate

#ifdef DEBUG_SLIDER
  printf("Pressed mDragStart=%d\n", mDragStart);
#endif

  if (!mScrollingWithAPZ) {
    SuppressDisplayport();
  }

  return NS_OK;
}

nsresult nsSliderFrame::StopDrag() {
  AddListener();
  DragThumb(false);

  mScrollingWithAPZ = false;

  UnsuppressDisplayport();

#ifdef MOZ_WIDGET_GTK
  nsIFrame* thumbFrame = mFrames.FirstChild();
  if (thumbFrame) {
    RefPtr<Element> thumb = thumbFrame->GetContent()->AsElement();
    thumb->UnsetAttr(kNameSpaceID_None, nsGkAtoms::active, true);
  }
#endif

  if (mChange) {
    StopRepeat();
    mChange = 0;
  }
  return NS_OK;
}

void nsSliderFrame::DragThumb(bool aGrabMouseEvents) {
  mDragFinished = !aGrabMouseEvents;

  nsIPresShell::SetCapturingContent(
      aGrabMouseEvents ? GetContent() : nullptr,
      aGrabMouseEvents ? CAPTURE_IGNOREALLOWED : 0);
}

bool nsSliderFrame::isDraggingThumb() const {
  return (nsIPresShell::GetCapturingContent() == GetContent());
}

void nsSliderFrame::AddListener() {
  if (!mMediator) {
    mMediator = new nsSliderMediator(this);
  }

  nsIFrame* thumbFrame = mFrames.FirstChild();
  if (!thumbFrame) {
    return;
  }
  thumbFrame->GetContent()->AddSystemEventListener(
      NS_LITERAL_STRING("mousedown"), mMediator, false, false);
  thumbFrame->GetContent()->AddSystemEventListener(
      NS_LITERAL_STRING("touchstart"), mMediator, false, false);
}

void nsSliderFrame::RemoveListener() {
  NS_ASSERTION(mMediator, "No listener was ever added!!");

  nsIFrame* thumbFrame = mFrames.FirstChild();
  if (!thumbFrame) return;

  thumbFrame->GetContent()->RemoveSystemEventListener(
      NS_LITERAL_STRING("mousedown"), mMediator, false);
}

bool nsSliderFrame::ShouldScrollForEvent(WidgetGUIEvent* aEvent) {
  switch (aEvent->mMessage) {
    case eTouchStart:
    case eTouchEnd:
      return true;
    case eMouseDown:
    case eMouseUp: {
      uint16_t button = aEvent->AsMouseEvent()->button;
#ifdef MOZ_WIDGET_GTK
      return (button == WidgetMouseEvent::eLeftButton) ||
             (button == WidgetMouseEvent::eRightButton && GetScrollToClick()) ||
             (button == WidgetMouseEvent::eMiddleButton && gMiddlePref &&
              !GetScrollToClick());
#else
      return (button == WidgetMouseEvent::eLeftButton) ||
             (button == WidgetMouseEvent::eMiddleButton && gMiddlePref);
#endif
    }
    default:
      return false;
  }
}

bool nsSliderFrame::ShouldScrollToClickForEvent(WidgetGUIEvent* aEvent) {
  if (!ShouldScrollForEvent(aEvent)) {
    return false;
  }

  if (aEvent->mMessage != eMouseDown && aEvent->mMessage != eTouchStart) {
    return false;
  }

#if defined(XP_MACOSX) || defined(MOZ_WIDGET_GTK)
  // On Mac and Linux, clicking the scrollbar thumb should never scroll to
  // click.
  if (IsEventOverThumb(aEvent)) {
    return false;
  }
#endif

  if (aEvent->mMessage == eTouchStart) {
    return GetScrollToClick();
  }

  WidgetMouseEvent* mouseEvent = aEvent->AsMouseEvent();
  if (mouseEvent->button == WidgetMouseEvent::eLeftButton) {
#ifdef XP_MACOSX
    bool invertPref = mouseEvent->IsAlt();
#else
    bool invertPref = mouseEvent->IsShift();
#endif
    return GetScrollToClick() != invertPref;
  }

#ifdef MOZ_WIDGET_GTK
  if (mouseEvent->button == WidgetMouseEvent::eRightButton) {
    return !GetScrollToClick();
  }
#endif

  return true;
}

bool nsSliderFrame::IsEventOverThumb(WidgetGUIEvent* aEvent) {
  nsIFrame* thumbFrame = mFrames.FirstChild();
  if (!thumbFrame) {
    return false;
  }

  nsPoint eventPoint;
  if (!GetEventPoint(aEvent, eventPoint)) {
    return false;
  }

  nsRect thumbRect = thumbFrame->GetRect();
#if defined(MOZ_WIDGET_GTK)
  /* Scrollbar track can have padding, so it's better to check that eventPoint
   * is inside of actual thumb, not just its one axis. The part of the scrollbar
   * track adjacent to thumb can actually receive events in GTK3 */
  return eventPoint.x >= thumbRect.x && eventPoint.x < thumbRect.XMost() &&
         eventPoint.y >= thumbRect.y && eventPoint.y < thumbRect.YMost();
#else
  bool isHorizontal = IsXULHorizontal();
  nscoord eventPos = isHorizontal ? eventPoint.x : eventPoint.y;
  nscoord thumbStart = isHorizontal ? thumbRect.x : thumbRect.y;
  nscoord thumbEnd = isHorizontal ? thumbRect.XMost() : thumbRect.YMost();

  return eventPos >= thumbStart && eventPos < thumbEnd;
#endif
}

NS_IMETHODIMP
nsSliderFrame::HandlePress(nsPresContext* aPresContext, WidgetGUIEvent* aEvent,
                           nsEventStatus* aEventStatus) {
  if (!ShouldScrollForEvent(aEvent) || ShouldScrollToClickForEvent(aEvent)) {
    return NS_OK;
  }

  if (IsEventOverThumb(aEvent)) {
    return NS_OK;
  }

  nsIFrame* thumbFrame = mFrames.FirstChild();
  if (!thumbFrame)  // display:none?
    return NS_OK;

  if (mContent->AsElement()->AttrValueIs(kNameSpaceID_None, nsGkAtoms::disabled,
                                         nsGkAtoms::_true, eCaseMatters))
    return NS_OK;

  nsRect thumbRect = thumbFrame->GetRect();

  nscoord change = 1;
  nsPoint eventPoint;
  if (!GetEventPoint(aEvent, eventPoint)) {
    return NS_OK;
  }

  if (IsXULHorizontal() ? eventPoint.x < thumbRect.x
                        : eventPoint.y < thumbRect.y)
    change = -1;

  mChange = change;
  DragThumb(true);
  // On Linux we want to keep scrolling in the direction indicated by |change|
  // until the mouse is released. On the other platforms we want to stop
  // scrolling as soon as the scrollbar thumb has reached the current mouse
  // position.
#ifdef MOZ_WIDGET_GTK
  nsRect clientRect;
  GetXULClientRect(clientRect);

  // Set the destination point to the very end of the scrollbar so that
  // scrolling doesn't stop halfway through.
  if (change > 0) {
    mDestinationPoint = nsPoint(clientRect.width, clientRect.height);
  } else {
    mDestinationPoint = nsPoint(0, 0);
  }
#else
  mDestinationPoint = eventPoint;
#endif
  StartRepeat();
  PageScroll(change);

  return NS_OK;
}

NS_IMETHODIMP
nsSliderFrame::HandleRelease(nsPresContext* aPresContext,
                             WidgetGUIEvent* aEvent,
                             nsEventStatus* aEventStatus) {
  StopRepeat();

  nsIFrame* scrollbar = GetScrollbar();
  nsScrollbarFrame* sb = do_QueryFrame(scrollbar);
  if (sb) {
    nsIScrollbarMediator* m = sb->GetScrollbarMediator();
    if (m) {
      m->ScrollbarReleased(sb);
    }
  }
  return NS_OK;
}

void nsSliderFrame::DestroyFrom(nsIFrame* aDestructRoot,
                                PostDestroyData& aPostDestroyData) {
  // tell our mediator if we have one we are gone.
  if (mMediator) {
    mMediator->SetSlider(nullptr);
    mMediator = nullptr;
  }
  StopRepeat();

  // call base class Destroy()
  nsBoxFrame::DestroyFrom(aDestructRoot, aPostDestroyData);
}

nsSize nsSliderFrame::GetXULPrefSize(nsBoxLayoutState& aState) {
  EnsureOrient();
  return nsBoxFrame::GetXULPrefSize(aState);
}

nsSize nsSliderFrame::GetXULMinSize(nsBoxLayoutState& aState) {
  EnsureOrient();

  // our min size is just our borders and padding
  return nsBox::GetXULMinSize(aState);
}

nsSize nsSliderFrame::GetXULMaxSize(nsBoxLayoutState& aState) {
  EnsureOrient();
  return nsBoxFrame::GetXULMaxSize(aState);
}

void nsSliderFrame::EnsureOrient() {
  nsIFrame* scrollbarBox = GetScrollbar();

  bool isHorizontal =
      (scrollbarBox->GetStateBits() & NS_STATE_IS_HORIZONTAL) != 0;
  if (isHorizontal)
    AddStateBits(NS_STATE_IS_HORIZONTAL);
  else
    RemoveStateBits(NS_STATE_IS_HORIZONTAL);
}

void nsSliderFrame::Notify(void) {
  bool stop = false;

  nsIFrame* thumbFrame = mFrames.FirstChild();
  if (!thumbFrame) {
    StopRepeat();
    return;
  }
  nsRect thumbRect = thumbFrame->GetRect();

  bool isHorizontal = IsXULHorizontal();

  // See if the thumb has moved past our destination point.
  // if it has we want to stop.
  if (isHorizontal) {
    if (mChange < 0) {
      if (thumbRect.x < mDestinationPoint.x) stop = true;
    } else {
      if (thumbRect.x + thumbRect.width > mDestinationPoint.x) stop = true;
    }
  } else {
    if (mChange < 0) {
      if (thumbRect.y < mDestinationPoint.y) stop = true;
    } else {
      if (thumbRect.y + thumbRect.height > mDestinationPoint.y) stop = true;
    }
  }

  if (stop) {
    StopRepeat();
  } else {
    PageScroll(mChange);
  }
}

void nsSliderFrame::PageScroll(nscoord aChange) {
  if (mContent->AsElement()->AttrValueIs(kNameSpaceID_None, nsGkAtoms::dir,
                                         nsGkAtoms::reverse, eCaseMatters)) {
    aChange = -aChange;
  }
  nsIFrame* scrollbar = GetScrollbar();
  nsScrollbarFrame* sb = do_QueryFrame(scrollbar);
  if (sb) {
    nsIScrollbarMediator* m = sb->GetScrollbarMediator();
    sb->SetIncrementToPage(aChange);
    if (m) {
      m->ScrollByPage(sb, aChange, nsIScrollbarMediator::ENABLE_SNAP);
      return;
    }
  }
  PageUpDown(aChange);
}

float nsSliderFrame::GetThumbRatio() const {
  // mRatio is in thumb app units per scrolled css pixels. Convert it to a
  // ratio of the thumb's CSS pixels per scrolled CSS pixels. (Note the thumb
  // is in the scrollframe's parent's space whereas the scrolled CSS pixels
  // are in the scrollframe's space).
  return mRatio / mozilla::AppUnitsPerCSSPixel();
}

void nsSliderFrame::AsyncScrollbarDragInitiated(uint64_t aDragBlockId) {
  mAPZDragInitiated = Some(aDragBlockId);
}

void nsSliderFrame::AsyncScrollbarDragRejected() {
  mScrollingWithAPZ = false;
  // Only suppress the displayport if we're still dragging the thumb.
  // Otherwise, no one will unsuppress it.
  if (isDraggingThumb()) {
    SuppressDisplayport();
  }
}

void nsSliderFrame::SuppressDisplayport() {
  if (!mSuppressionActive) {
    nsIPresShell* shell = PresShell();
    MOZ_ASSERT(shell);
    shell->SuppressDisplayport(true);
    mSuppressionActive = true;
  }
}

void nsSliderFrame::UnsuppressDisplayport() {
  if (mSuppressionActive) {
    nsIPresShell* shell = PresShell();
    MOZ_ASSERT(shell);
    shell->SuppressDisplayport(false);
    mSuppressionActive = false;
  }
}

bool nsSliderFrame::OnlySystemGroupDispatch(EventMessage aMessage) const {
  // If we are in a native anonymous subtree, do not dispatch mouse-move events
  // targeted at this slider frame to web content. This matches the behaviour
  // of other browsers.
  return aMessage == eMouseMove && isDraggingThumb() &&
         GetContent()->IsInNativeAnonymousSubtree();
}

NS_IMPL_ISUPPORTS(nsSliderMediator, nsIDOMEventListener)