From 6bf0a5cb5034a7e684dcc3500e841785237ce2dd Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Sun, 7 Apr 2024 19:32:43 +0200
Subject: Adding upstream version 1:115.7.0.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 dom/events/WheelHandlingHelper.cpp | 872 +++++++++++++++++++++++++++++++++++++
 1 file changed, 872 insertions(+)
 create mode 100644 dom/events/WheelHandlingHelper.cpp

(limited to 'dom/events/WheelHandlingHelper.cpp')

diff --git a/dom/events/WheelHandlingHelper.cpp b/dom/events/WheelHandlingHelper.cpp
new file mode 100644
index 0000000000..3b5653c50e
--- /dev/null
+++ b/dom/events/WheelHandlingHelper.cpp
@@ -0,0 +1,872 @@
+/* -*- 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 "WheelHandlingHelper.h"
+
+#include <utility>  // for std::swap
+
+#include "mozilla/EventDispatcher.h"
+#include "mozilla/EventStateManager.h"
+#include "mozilla/MouseEvents.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/StaticPrefs_mousewheel.h"
+#include "mozilla/StaticPrefs_test.h"
+#include "mozilla/TextControlElement.h"
+#include "mozilla/dom/WheelEventBinding.h"
+#include "nsCOMPtr.h"
+#include "nsContentUtils.h"
+#include "nsIContent.h"
+#include "nsIContentInlines.h"
+#include "mozilla/dom/Document.h"
+#include "DocumentInlines.h"  // for Document and HTMLBodyElement
+#include "nsIScrollableFrame.h"
+#include "nsITimer.h"
+#include "nsPresContext.h"
+#include "prtime.h"
+#include "Units.h"
+#include "ScrollAnimationPhysics.h"
+
+namespace mozilla {
+
+/******************************************************************/
+/* mozilla::DeltaValues                                           */
+/******************************************************************/
+
+DeltaValues::DeltaValues(WidgetWheelEvent* aEvent)
+    : deltaX(aEvent->mDeltaX), deltaY(aEvent->mDeltaY) {}
+
+/******************************************************************/
+/* mozilla::WheelHandlingUtils                                    */
+/******************************************************************/
+
+/* static */
+bool WheelHandlingUtils::CanScrollInRange(nscoord aMin, nscoord aValue,
+                                          nscoord aMax, double aDirection) {
+  return aDirection > 0.0 ? aValue < static_cast<double>(aMax)
+                          : static_cast<double>(aMin) < aValue;
+}
+
+/* static */
+bool WheelHandlingUtils::CanScrollOn(nsIFrame* aFrame, double aDirectionX,
+                                     double aDirectionY) {
+  nsIScrollableFrame* scrollableFrame = do_QueryFrame(aFrame);
+  if (!scrollableFrame) {
+    return false;
+  }
+  return CanScrollOn(scrollableFrame, aDirectionX, aDirectionY);
+}
+
+/* static */
+bool WheelHandlingUtils::CanScrollOn(nsIScrollableFrame* aScrollFrame,
+                                     double aDirectionX, double aDirectionY) {
+  MOZ_ASSERT(aScrollFrame);
+  NS_ASSERTION(aDirectionX || aDirectionY,
+               "One of the delta values must be non-zero at least");
+
+  nsPoint scrollPt = aScrollFrame->GetVisualViewportOffset();
+  nsRect scrollRange = aScrollFrame->GetScrollRangeForUserInputEvents();
+  layers::ScrollDirections directions =
+      aScrollFrame->GetAvailableScrollingDirectionsForUserInputEvents();
+
+  return ((aDirectionX != 0.0) &&
+          (directions.contains(layers::ScrollDirection::eHorizontal)) &&
+          CanScrollInRange(scrollRange.x, scrollPt.x, scrollRange.XMost(),
+                           aDirectionX)) ||
+         ((aDirectionY != 0.0) &&
+          (directions.contains(layers::ScrollDirection::eVertical)) &&
+          CanScrollInRange(scrollRange.y, scrollPt.y, scrollRange.YMost(),
+                           aDirectionY));
+}
+
+/*static*/ Maybe<layers::ScrollDirection>
+WheelHandlingUtils::GetDisregardedWheelScrollDirection(const nsIFrame* aFrame) {
+  nsIContent* content = aFrame->GetContent();
+  if (!content) {
+    return Nothing();
+  }
+  TextControlElement* textControlElement = TextControlElement::FromNodeOrNull(
+      content->IsInNativeAnonymousSubtree()
+          ? content->GetClosestNativeAnonymousSubtreeRootParentOrHost()
+          : content);
+  if (!textControlElement || !textControlElement->IsSingleLineTextControl()) {
+    return Nothing();
+  }
+  // Disregard scroll in the block-flow direction by mouse wheel on a
+  // single-line text control. For instance, in tranditional Chinese writing
+  // system, a single-line text control cannot be scrolled horizontally with
+  // mouse wheel even if they overflow at the right and left edges; Whereas in
+  // latin-based writing system, a single-line text control cannot be scrolled
+  // vertically with mouse wheel even if they overflow at the top and bottom
+  // edges
+  return Some(aFrame->GetWritingMode().IsVertical()
+                  ? layers::ScrollDirection::eHorizontal
+                  : layers::ScrollDirection::eVertical);
+}
+
+/******************************************************************/
+/* mozilla::WheelTransaction                                      */
+/******************************************************************/
+
+AutoWeakFrame WheelTransaction::sScrollTargetFrame(nullptr);
+AutoWeakFrame WheelTransaction::sEventTargetFrame(nullptr);
+bool WheelTransaction::sHandledByApz(false);
+uint32_t WheelTransaction::sTime = 0;
+uint32_t WheelTransaction::sMouseMoved = 0;
+nsITimer* WheelTransaction::sTimer = nullptr;
+int32_t WheelTransaction::sScrollSeriesCounter = 0;
+bool WheelTransaction::sOwnScrollbars = false;
+
+/* static */
+bool WheelTransaction::OutOfTime(uint32_t aBaseTime, uint32_t aThreshold) {
+  uint32_t now = PR_IntervalToMilliseconds(PR_IntervalNow());
+  return (now - aBaseTime > aThreshold);
+}
+
+/* static */
+void WheelTransaction::OwnScrollbars(bool aOwn) { sOwnScrollbars = aOwn; }
+
+/* static */
+void WheelTransaction::BeginTransaction(nsIFrame* aScrollTargetFrame,
+                                        nsIFrame* aEventTargetFrame,
+                                        const WidgetWheelEvent* aEvent) {
+  NS_ASSERTION(!sScrollTargetFrame && !sEventTargetFrame,
+               "previous transaction is not finished!");
+  MOZ_ASSERT(aEvent->mMessage == eWheel,
+             "Transaction must be started with a wheel event");
+
+  ScrollbarsForWheel::OwnWheelTransaction(false);
+  sScrollTargetFrame = aScrollTargetFrame;
+
+  // Only set the static event target if wheel event groups are enabled.
+  if (StaticPrefs::dom_event_wheel_event_groups_enabled()) {
+    // Set a static event target for the wheel transaction. This will be used
+    // to override the event target frame when computing the event target from
+    // input coordinates. When this preference is not set or there is no stored
+    // event target for the current wheel transaction, the event target will
+    // not be overridden by the current wheel transaction, but will be computed
+    // from the input coordinates.
+    sEventTargetFrame = aEventTargetFrame;
+    // If the wheel events will be handled by APZ, set a flag here. We can use
+    // this later to determine if we need to scroll snap at the end of the
+    // wheel operation.
+    sHandledByApz = aEvent->mFlags.mHandledByAPZ;
+  }
+
+  sScrollSeriesCounter = 0;
+  if (!UpdateTransaction(aEvent)) {
+    NS_ERROR("BeginTransaction is called even cannot scroll the frame");
+    EndTransaction();
+  }
+}
+
+/* static */
+bool WheelTransaction::UpdateTransaction(const WidgetWheelEvent* aEvent) {
+  nsIFrame* scrollToFrame = GetScrollTargetFrame();
+  nsIScrollableFrame* scrollableFrame = scrollToFrame->GetScrollTargetFrame();
+  if (scrollableFrame) {
+    scrollToFrame = do_QueryFrame(scrollableFrame);
+  }
+
+  if (!WheelHandlingUtils::CanScrollOn(scrollToFrame, aEvent->mDeltaX,
+                                       aEvent->mDeltaY)) {
+    OnFailToScrollTarget();
+    // We should not modify the transaction state when the view will not be
+    // scrolled actually.
+    return false;
+  }
+
+  SetTimeout();
+
+  if (sScrollSeriesCounter != 0 &&
+      OutOfTime(sTime, StaticPrefs::mousewheel_scroll_series_timeout())) {
+    sScrollSeriesCounter = 0;
+  }
+  sScrollSeriesCounter++;
+
+  // We should use current time instead of WidgetEvent.time.
+  // 1. Some events doesn't have the correct creation time.
+  // 2. If the computer runs slowly by other processes eating the CPU resource,
+  //    the event creation time doesn't keep real time.
+  sTime = PR_IntervalToMilliseconds(PR_IntervalNow());
+  sMouseMoved = 0;
+  return true;
+}
+
+/* static */
+void WheelTransaction::MayEndTransaction() {
+  if (!sOwnScrollbars && ScrollbarsForWheel::IsActive()) {
+    ScrollbarsForWheel::OwnWheelTransaction(true);
+  } else {
+    EndTransaction();
+  }
+}
+
+/* static */
+void WheelTransaction::EndTransaction() {
+  if (sTimer) {
+    sTimer->Cancel();
+  }
+  sScrollTargetFrame = nullptr;
+  sEventTargetFrame = nullptr;
+  sScrollSeriesCounter = 0;
+  sHandledByApz = false;
+  if (sOwnScrollbars) {
+    sOwnScrollbars = false;
+    ScrollbarsForWheel::OwnWheelTransaction(false);
+    ScrollbarsForWheel::Inactivate();
+  }
+}
+
+/* static */
+bool WheelTransaction::WillHandleDefaultAction(
+    WidgetWheelEvent* aWheelEvent, AutoWeakFrame& aScrollTargetWeakFrame,
+    AutoWeakFrame& aEventTargetWeakFrame) {
+  nsIFrame* lastTargetFrame = GetScrollTargetFrame();
+  if (!lastTargetFrame) {
+    BeginTransaction(aScrollTargetWeakFrame.GetFrame(),
+                     aEventTargetWeakFrame.GetFrame(), aWheelEvent);
+  } else if (lastTargetFrame != aScrollTargetWeakFrame.GetFrame()) {
+    EndTransaction();
+    BeginTransaction(aScrollTargetWeakFrame.GetFrame(),
+                     aEventTargetWeakFrame.GetFrame(), aWheelEvent);
+  } else {
+    UpdateTransaction(aWheelEvent);
+  }
+
+  // When the wheel event will not be handled with any frames,
+  // UpdateTransaction() fires MozMouseScrollFailed event which is for
+  // automated testing.  In the event handler, the target frame might be
+  // destroyed.  Then, the caller shouldn't try to handle the default action.
+  if (!aScrollTargetWeakFrame.IsAlive()) {
+    EndTransaction();
+    return false;
+  }
+
+  return true;
+}
+
+/* static */
+void WheelTransaction::OnEvent(WidgetEvent* aEvent) {
+  if (!sScrollTargetFrame) {
+    return;
+  }
+
+  if (OutOfTime(sTime, StaticPrefs::mousewheel_transaction_timeout())) {
+    // Even if the scroll event which is handled after timeout, but onTimeout
+    // was not fired by timer, then the scroll event will scroll old frame,
+    // therefore, we should call OnTimeout here and ensure to finish the old
+    // transaction.
+    OnTimeout(nullptr, nullptr);
+    return;
+  }
+
+  switch (aEvent->mMessage) {
+    case eWheel:
+      if (sMouseMoved != 0 &&
+          OutOfTime(sMouseMoved,
+                    StaticPrefs::mousewheel_transaction_ignoremovedelay())) {
+        // Terminate the current mousewheel transaction if the mouse moved more
+        // than ignoremovedelay milliseconds ago
+        EndTransaction();
+      }
+      return;
+    case eMouseMove:
+    case eDragOver: {
+      WidgetMouseEvent* mouseEvent = aEvent->AsMouseEvent();
+      if (mouseEvent->IsReal()) {
+        // If the cursor is moving to be outside the frame,
+        // terminate the scrollwheel transaction.
+        LayoutDeviceIntPoint pt = GetScreenPoint(mouseEvent);
+        auto r = LayoutDeviceIntRect::FromAppUnitsToNearest(
+            sScrollTargetFrame->GetScreenRectInAppUnits(),
+            sScrollTargetFrame->PresContext()->AppUnitsPerDevPixel());
+        if (!r.Contains(pt)) {
+          EndTransaction();
+          return;
+        }
+
+        // For mouse move events where the wheel transaction is still valid, the
+        // stored event target should be reset.
+        sEventTargetFrame = nullptr;
+
+        // If the cursor is moving inside the frame, and it is less than
+        // ignoremovedelay milliseconds since the last scroll operation, ignore
+        // the mouse move; otherwise, record the current mouse move time to be
+        // checked later
+        if (!sMouseMoved &&
+            OutOfTime(sTime,
+                      StaticPrefs::mousewheel_transaction_ignoremovedelay())) {
+          sMouseMoved = PR_IntervalToMilliseconds(PR_IntervalNow());
+        }
+      }
+      return;
+    }
+    case eKeyPress:
+    case eKeyUp:
+    case eKeyDown:
+    case eMouseUp:
+    case eMouseDown:
+    case eMouseDoubleClick:
+    case eMouseAuxClick:
+    case eMouseClick:
+    case eContextMenu:
+    case eDrop:
+      EndTransaction();
+      return;
+    default:
+      break;
+  }
+}
+
+/* static */
+void WheelTransaction::OnRemoveElement(nsIContent* aContent) {
+  // If dom.event.wheel-event-groups.enabled is not set or we have no current
+  // wheel event transaction there is no internal state to be updated.
+  if (!sEventTargetFrame) {
+    return;
+  }
+
+  if (sEventTargetFrame->GetContent() == aContent) {
+    // Only invalidate the wheel transaction event target frame when the
+    // remove target is the event target of the wheel event group. The
+    // scroll target frame of the wheel event group may still be valid.
+    //
+    // With the stored event target unset, the target for any following
+    // events will be the frame found using the input coordinates.
+    sEventTargetFrame = nullptr;
+  }
+}
+
+/* static */
+void WheelTransaction::Shutdown() { NS_IF_RELEASE(sTimer); }
+
+/* static */
+void WheelTransaction::OnFailToScrollTarget() {
+  MOZ_ASSERT(sScrollTargetFrame, "We don't have mouse scrolling transaction");
+
+  if (StaticPrefs::test_mousescroll()) {
+    // This event is used for automated tests, see bug 442774.
+    nsContentUtils::DispatchEventOnlyToChrome(
+        sScrollTargetFrame->GetContent()->OwnerDoc(),
+        sScrollTargetFrame->GetContent(), u"MozMouseScrollFailed"_ns,
+        CanBubble::eYes, Cancelable::eYes);
+  }
+  // The target frame might be destroyed in the event handler, at that time,
+  // we need to finish the current transaction
+  if (!sScrollTargetFrame) {
+    EndTransaction();
+  }
+}
+
+/* static */
+void WheelTransaction::OnTimeout(nsITimer* aTimer, void* aClosure) {
+  if (!sScrollTargetFrame) {
+    // The transaction target was destroyed already
+    EndTransaction();
+    return;
+  }
+  // Store the sScrollTargetFrame, the variable becomes null in EndTransaction.
+  nsIFrame* frame = sScrollTargetFrame;
+  // We need to finish current transaction before DOM event firing. Because
+  // the next DOM event might create strange situation for us.
+  MayEndTransaction();
+
+  if (StaticPrefs::test_mousescroll()) {
+    // This event is used for automated tests, see bug 442774.
+    nsContentUtils::DispatchEventOnlyToChrome(
+        frame->GetContent()->OwnerDoc(), frame->GetContent(),
+        u"MozMouseScrollTransactionTimeout"_ns, CanBubble::eYes,
+        Cancelable::eYes);
+  }
+}
+
+/* static */
+void WheelTransaction::SetTimeout() {
+  if (!sTimer) {
+    sTimer = NS_NewTimer().take();
+    if (!sTimer) {
+      return;
+    }
+  }
+  sTimer->Cancel();
+  DebugOnly<nsresult> rv = sTimer->InitWithNamedFuncCallback(
+      OnTimeout, nullptr, StaticPrefs::mousewheel_transaction_timeout(),
+      nsITimer::TYPE_ONE_SHOT, "WheelTransaction::SetTimeout");
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv),
+                       "nsITimer::InitWithFuncCallback failed");
+}
+
+/* static */
+LayoutDeviceIntPoint WheelTransaction::GetScreenPoint(WidgetGUIEvent* aEvent) {
+  NS_ASSERTION(aEvent, "aEvent is null");
+  NS_ASSERTION(aEvent->mWidget, "aEvent-mWidget is null");
+  return aEvent->mRefPoint + aEvent->mWidget->WidgetToScreenOffset();
+}
+
+/* static */
+DeltaValues WheelTransaction::AccelerateWheelDelta(WidgetWheelEvent* aEvent) {
+  DeltaValues result = OverrideSystemScrollSpeed(aEvent);
+
+  // Don't accelerate the delta values if the event isn't line scrolling.
+  if (aEvent->mDeltaMode != dom::WheelEvent_Binding::DOM_DELTA_LINE) {
+    return result;
+  }
+
+  // Accelerate by the sScrollSeriesCounter
+  int32_t start = StaticPrefs::mousewheel_acceleration_start();
+  if (start >= 0 && sScrollSeriesCounter >= start) {
+    int32_t factor = StaticPrefs::mousewheel_acceleration_factor();
+    if (factor > 0) {
+      result.deltaX = ComputeAcceleratedWheelDelta(result.deltaX, factor);
+      result.deltaY = ComputeAcceleratedWheelDelta(result.deltaY, factor);
+    }
+  }
+
+  return result;
+}
+
+/* static */
+double WheelTransaction::ComputeAcceleratedWheelDelta(double aDelta,
+                                                      int32_t aFactor) {
+  return mozilla::ComputeAcceleratedWheelDelta(aDelta, sScrollSeriesCounter,
+                                               aFactor);
+}
+
+/* static */
+DeltaValues WheelTransaction::OverrideSystemScrollSpeed(
+    WidgetWheelEvent* aEvent) {
+  MOZ_ASSERT(sScrollTargetFrame, "We don't have mouse scrolling transaction");
+
+  // If the event doesn't scroll to both X and Y, we don't need to do anything
+  // here.
+  if (!aEvent->mDeltaX && !aEvent->mDeltaY) {
+    return DeltaValues(aEvent);
+  }
+
+  return DeltaValues(aEvent->OverriddenDeltaX(), aEvent->OverriddenDeltaY());
+}
+
+/******************************************************************/
+/* mozilla::ScrollbarsForWheel                                    */
+/******************************************************************/
+
+const DeltaValues ScrollbarsForWheel::directions[kNumberOfTargets] = {
+    DeltaValues(-1, 0), DeltaValues(+1, 0), DeltaValues(0, -1),
+    DeltaValues(0, +1)};
+
+AutoWeakFrame ScrollbarsForWheel::sActiveOwner = nullptr;
+AutoWeakFrame ScrollbarsForWheel::sActivatedScrollTargets[kNumberOfTargets] = {
+    nullptr, nullptr, nullptr, nullptr};
+
+bool ScrollbarsForWheel::sHadWheelStart = false;
+bool ScrollbarsForWheel::sOwnWheelTransaction = false;
+
+/* static */
+void ScrollbarsForWheel::PrepareToScrollText(EventStateManager* aESM,
+                                             nsIFrame* aTargetFrame,
+                                             WidgetWheelEvent* aEvent) {
+  if (aEvent->mMessage == eWheelOperationStart) {
+    WheelTransaction::OwnScrollbars(false);
+    if (!IsActive()) {
+      TemporarilyActivateAllPossibleScrollTargets(aESM, aTargetFrame, aEvent);
+      sHadWheelStart = true;
+    }
+  } else {
+    DeactivateAllTemporarilyActivatedScrollTargets();
+  }
+}
+
+/* static */
+void ScrollbarsForWheel::SetActiveScrollTarget(
+    nsIScrollableFrame* aScrollTarget) {
+  if (!sHadWheelStart) {
+    return;
+  }
+  nsIScrollbarMediator* scrollbarMediator = do_QueryFrame(aScrollTarget);
+  if (!scrollbarMediator) {
+    return;
+  }
+  sHadWheelStart = false;
+  sActiveOwner = do_QueryFrame(aScrollTarget);
+  scrollbarMediator->ScrollbarActivityStarted();
+}
+
+/* static */
+void ScrollbarsForWheel::MayInactivate() {
+  if (!sOwnWheelTransaction && WheelTransaction::GetScrollTargetFrame()) {
+    WheelTransaction::OwnScrollbars(true);
+  } else {
+    Inactivate();
+  }
+}
+
+/* static */
+void ScrollbarsForWheel::Inactivate() {
+  nsIScrollbarMediator* scrollbarMediator = do_QueryFrame(sActiveOwner);
+  if (scrollbarMediator) {
+    scrollbarMediator->ScrollbarActivityStopped();
+  }
+  sActiveOwner = nullptr;
+  DeactivateAllTemporarilyActivatedScrollTargets();
+  if (sOwnWheelTransaction) {
+    sOwnWheelTransaction = false;
+    WheelTransaction::OwnScrollbars(false);
+    WheelTransaction::EndTransaction();
+  }
+}
+
+/* static */
+bool ScrollbarsForWheel::IsActive() {
+  if (sActiveOwner) {
+    return true;
+  }
+  for (size_t i = 0; i < kNumberOfTargets; ++i) {
+    if (sActivatedScrollTargets[i]) {
+      return true;
+    }
+  }
+  return false;
+}
+
+/* static */
+void ScrollbarsForWheel::OwnWheelTransaction(bool aOwn) {
+  sOwnWheelTransaction = aOwn;
+}
+
+/* static */
+void ScrollbarsForWheel::TemporarilyActivateAllPossibleScrollTargets(
+    EventStateManager* aESM, nsIFrame* aTargetFrame, WidgetWheelEvent* aEvent) {
+  for (size_t i = 0; i < kNumberOfTargets; i++) {
+    const DeltaValues* dir = &directions[i];
+    AutoWeakFrame* scrollTarget = &sActivatedScrollTargets[i];
+    MOZ_ASSERT(!*scrollTarget, "scroll target still temporarily activated!");
+    nsIScrollableFrame* target = do_QueryFrame(aESM->ComputeScrollTarget(
+        aTargetFrame, dir->deltaX, dir->deltaY, aEvent,
+        EventStateManager::COMPUTE_DEFAULT_ACTION_TARGET));
+    nsIScrollbarMediator* scrollbarMediator = do_QueryFrame(target);
+    if (scrollbarMediator) {
+      nsIFrame* targetFrame = do_QueryFrame(target);
+      *scrollTarget = targetFrame;
+      scrollbarMediator->ScrollbarActivityStarted();
+    }
+  }
+}
+
+/* static */
+void ScrollbarsForWheel::DeactivateAllTemporarilyActivatedScrollTargets() {
+  for (size_t i = 0; i < kNumberOfTargets; i++) {
+    AutoWeakFrame* scrollTarget = &sActivatedScrollTargets[i];
+    if (*scrollTarget) {
+      nsIScrollbarMediator* scrollbarMediator = do_QueryFrame(*scrollTarget);
+      if (scrollbarMediator) {
+        scrollbarMediator->ScrollbarActivityStopped();
+      }
+      *scrollTarget = nullptr;
+    }
+  }
+}
+
+/******************************************************************/
+/* mozilla::WheelDeltaHorizontalizer                              */
+/******************************************************************/
+
+void WheelDeltaHorizontalizer::Horizontalize() {
+  MOZ_ASSERT(!mWheelEvent.mDeltaValuesHorizontalizedForDefaultHandler,
+             "Wheel delta values in one wheel scroll event are being adjusted "
+             "a second time");
+
+  // Log the old values.
+  mOldDeltaX = mWheelEvent.mDeltaX;
+  mOldDeltaZ = mWheelEvent.mDeltaZ;
+  mOldOverflowDeltaX = mWheelEvent.mOverflowDeltaX;
+  mOldLineOrPageDeltaX = mWheelEvent.mLineOrPageDeltaX;
+
+  // Move deltaY values to deltaX and set both deltaY and deltaZ to 0.
+  mWheelEvent.mDeltaX = mWheelEvent.mDeltaY;
+  mWheelEvent.mDeltaY = 0.0;
+  mWheelEvent.mDeltaZ = 0.0;
+  mWheelEvent.mOverflowDeltaX = mWheelEvent.mOverflowDeltaY;
+  mWheelEvent.mOverflowDeltaY = 0.0;
+  mWheelEvent.mLineOrPageDeltaX = mWheelEvent.mLineOrPageDeltaY;
+  mWheelEvent.mLineOrPageDeltaY = 0;
+
+  // Mark it horizontalized in order to restore the delta values when this
+  // instance is being destroyed.
+  mWheelEvent.mDeltaValuesHorizontalizedForDefaultHandler = true;
+  mHorizontalized = true;
+}
+
+void WheelDeltaHorizontalizer::CancelHorizontalization() {
+  // Restore the horizontalized delta.
+  if (mHorizontalized &&
+      mWheelEvent.mDeltaValuesHorizontalizedForDefaultHandler) {
+    mWheelEvent.mDeltaY = mWheelEvent.mDeltaX;
+    mWheelEvent.mDeltaX = mOldDeltaX;
+    mWheelEvent.mDeltaZ = mOldDeltaZ;
+    mWheelEvent.mOverflowDeltaY = mWheelEvent.mOverflowDeltaX;
+    mWheelEvent.mOverflowDeltaX = mOldOverflowDeltaX;
+    mWheelEvent.mLineOrPageDeltaY = mWheelEvent.mLineOrPageDeltaX;
+    mWheelEvent.mLineOrPageDeltaX = mOldLineOrPageDeltaX;
+    mWheelEvent.mDeltaValuesHorizontalizedForDefaultHandler = false;
+    mHorizontalized = false;
+  }
+}
+
+WheelDeltaHorizontalizer::~WheelDeltaHorizontalizer() {
+  CancelHorizontalization();
+}
+
+/******************************************************************/
+/* mozilla::AutoDirWheelDeltaAdjuster                             */
+/******************************************************************/
+
+bool AutoDirWheelDeltaAdjuster::ShouldBeAdjusted() {
+  // Sometimes, this function can be called more than one time. If we have
+  // already checked if the scroll should be adjusted, there's no need to check
+  // it again.
+  if (mCheckedIfShouldBeAdjusted) {
+    return mShouldBeAdjusted;
+  }
+  mCheckedIfShouldBeAdjusted = true;
+
+  // For an auto-dir wheel scroll, if all the following conditions are met, we
+  // should adjust X and Y values:
+  // 1. There is only one non-zero value between DeltaX and DeltaY.
+  // 2. There is only one direction for the target that overflows and is
+  //    scrollable with wheel.
+  // 3. The direction described in Condition 1 is orthogonal to the one
+  // described in Condition 2.
+  if ((mDeltaX && mDeltaY) || (!mDeltaX && !mDeltaY)) {
+    return false;
+  }
+  if (mDeltaX) {
+    if (CanScrollAlongXAxis()) {
+      return false;
+    }
+    if (IsHorizontalContentRightToLeft()) {
+      mShouldBeAdjusted =
+          mDeltaX > 0 ? CanScrollUpwards() : CanScrollDownwards();
+    } else {
+      mShouldBeAdjusted =
+          mDeltaX < 0 ? CanScrollUpwards() : CanScrollDownwards();
+    }
+    return mShouldBeAdjusted;
+  }
+  MOZ_ASSERT(0 != mDeltaY);
+  if (CanScrollAlongYAxis()) {
+    return false;
+  }
+  if (IsHorizontalContentRightToLeft()) {
+    mShouldBeAdjusted =
+        mDeltaY > 0 ? CanScrollLeftwards() : CanScrollRightwards();
+  } else {
+    mShouldBeAdjusted =
+        mDeltaY < 0 ? CanScrollLeftwards() : CanScrollRightwards();
+  }
+  return mShouldBeAdjusted;
+}
+
+void AutoDirWheelDeltaAdjuster::Adjust() {
+  if (!ShouldBeAdjusted()) {
+    return;
+  }
+  std::swap(mDeltaX, mDeltaY);
+  if (IsHorizontalContentRightToLeft()) {
+    mDeltaX *= -1;
+    mDeltaY *= -1;
+  }
+  mShouldBeAdjusted = false;
+  OnAdjusted();
+}
+
+/******************************************************************/
+/* mozilla::ESMAutoDirWheelDeltaAdjuster                          */
+/******************************************************************/
+
+ESMAutoDirWheelDeltaAdjuster::ESMAutoDirWheelDeltaAdjuster(
+    WidgetWheelEvent& aEvent, nsIFrame& aScrollFrame, bool aHonoursRoot)
+    : AutoDirWheelDeltaAdjuster(aEvent.mDeltaX, aEvent.mDeltaY),
+      mLineOrPageDeltaX(aEvent.mLineOrPageDeltaX),
+      mLineOrPageDeltaY(aEvent.mLineOrPageDeltaY),
+      mOverflowDeltaX(aEvent.mOverflowDeltaX),
+      mOverflowDeltaY(aEvent.mOverflowDeltaY) {
+  mScrollTargetFrame = aScrollFrame.GetScrollTargetFrame();
+  MOZ_ASSERT(mScrollTargetFrame);
+
+  nsIFrame* honouredFrame = nullptr;
+  if (aHonoursRoot) {
+    // If we are going to honour root, first try to get the frame for <body> as
+    // the honoured root, because <body> is in preference to <html> if the
+    // current document is an HTML document.
+    dom::Document* document = aScrollFrame.PresShell()->GetDocument();
+    if (document) {
+      dom::Element* bodyElement = document->GetBodyElement();
+      if (bodyElement) {
+        honouredFrame = bodyElement->GetPrimaryFrame();
+      }
+    }
+
+    if (!honouredFrame) {
+      // If there is no <body> frame, fall back to the real root frame.
+      honouredFrame = aScrollFrame.PresShell()->GetRootScrollFrame();
+    }
+
+    if (!honouredFrame) {
+      // If there is no root scroll frame, fall back to the current scrolling
+      // frame.
+      honouredFrame = &aScrollFrame;
+    }
+  } else {
+    honouredFrame = &aScrollFrame;
+  }
+
+  WritingMode writingMode = honouredFrame->GetWritingMode();
+  WritingMode::BlockDir blockDir = writingMode.GetBlockDir();
+  WritingMode::InlineDir inlineDir = writingMode.GetInlineDir();
+  // Get whether the honoured frame's content in the horizontal direction starts
+  // from right to left(E.g. it's true either if "writing-mode: vertical-rl", or
+  // if "writing-mode: horizontal-tb; direction: rtl;" in CSS).
+  mIsHorizontalContentRightToLeft =
+      (blockDir == WritingMode::BlockDir::eBlockRL ||
+       (blockDir == WritingMode::BlockDir::eBlockTB &&
+        inlineDir == WritingMode::InlineDir::eInlineRTL));
+}
+
+void ESMAutoDirWheelDeltaAdjuster::OnAdjusted() {
+  // Adjust() only adjusted basic deltaX and deltaY, which are not enough for
+  // ESM, we should continue to adjust line-or-page and overflow values.
+  if (mDeltaX) {
+    // A vertical scroll was adjusted to be horizontal.
+    MOZ_ASSERT(0 == mDeltaY);
+
+    mLineOrPageDeltaX = mLineOrPageDeltaY;
+    mLineOrPageDeltaY = 0;
+    mOverflowDeltaX = mOverflowDeltaY;
+    mOverflowDeltaY = 0;
+  } else {
+    // A horizontal scroll was adjusted to be vertical.
+    MOZ_ASSERT(0 != mDeltaY);
+
+    mLineOrPageDeltaY = mLineOrPageDeltaX;
+    mLineOrPageDeltaX = 0;
+    mOverflowDeltaY = mOverflowDeltaX;
+    mOverflowDeltaX = 0;
+  }
+  if (mIsHorizontalContentRightToLeft) {
+    // If in RTL writing mode, reverse the side the scroll will go towards.
+    mLineOrPageDeltaX *= -1;
+    mLineOrPageDeltaY *= -1;
+    mOverflowDeltaX *= -1;
+    mOverflowDeltaY *= -1;
+  }
+}
+
+bool ESMAutoDirWheelDeltaAdjuster::CanScrollAlongXAxis() const {
+  return mScrollTargetFrame->GetAvailableScrollingDirections().contains(
+      layers::ScrollDirection::eHorizontal);
+}
+
+bool ESMAutoDirWheelDeltaAdjuster::CanScrollAlongYAxis() const {
+  return mScrollTargetFrame->GetAvailableScrollingDirections().contains(
+      layers::ScrollDirection::eVertical);
+}
+
+bool ESMAutoDirWheelDeltaAdjuster::CanScrollUpwards() const {
+  nsPoint scrollPt = mScrollTargetFrame->GetScrollPosition();
+  nsRect scrollRange = mScrollTargetFrame->GetScrollRange();
+  return static_cast<double>(scrollRange.y) < scrollPt.y;
+}
+
+bool ESMAutoDirWheelDeltaAdjuster::CanScrollDownwards() const {
+  nsPoint scrollPt = mScrollTargetFrame->GetScrollPosition();
+  nsRect scrollRange = mScrollTargetFrame->GetScrollRange();
+  return static_cast<double>(scrollRange.YMost()) > scrollPt.y;
+}
+
+bool ESMAutoDirWheelDeltaAdjuster::CanScrollLeftwards() const {
+  nsPoint scrollPt = mScrollTargetFrame->GetScrollPosition();
+  nsRect scrollRange = mScrollTargetFrame->GetScrollRange();
+  return static_cast<double>(scrollRange.x) < scrollPt.x;
+}
+
+bool ESMAutoDirWheelDeltaAdjuster::CanScrollRightwards() const {
+  nsPoint scrollPt = mScrollTargetFrame->GetScrollPosition();
+  nsRect scrollRange = mScrollTargetFrame->GetScrollRange();
+  return static_cast<double>(scrollRange.XMost()) > scrollPt.x;
+}
+
+bool ESMAutoDirWheelDeltaAdjuster::IsHorizontalContentRightToLeft() const {
+  return mIsHorizontalContentRightToLeft;
+}
+
+/******************************************************************/
+/* mozilla::ESMAutoDirWheelDeltaRestorer                          */
+/******************************************************************/
+
+/*explicit*/
+ESMAutoDirWheelDeltaRestorer::ESMAutoDirWheelDeltaRestorer(
+    WidgetWheelEvent& aEvent)
+    : mEvent(aEvent),
+      mOldDeltaX(aEvent.mDeltaX),
+      mOldDeltaY(aEvent.mDeltaY),
+      mOldLineOrPageDeltaX(aEvent.mLineOrPageDeltaX),
+      mOldLineOrPageDeltaY(aEvent.mLineOrPageDeltaY),
+      mOldOverflowDeltaX(aEvent.mOverflowDeltaX),
+      mOldOverflowDeltaY(aEvent.mOverflowDeltaY) {}
+
+ESMAutoDirWheelDeltaRestorer::~ESMAutoDirWheelDeltaRestorer() {
+  if (mOldDeltaX == mEvent.mDeltaX || mOldDeltaY == mEvent.mDeltaY) {
+    // The delta of the event wasn't adjusted during the lifetime of this
+    // |ESMAutoDirWheelDeltaRestorer| instance. No need to restore it.
+    return;
+  }
+
+  bool forRTL = false;
+
+  // First, restore the basic deltaX and deltaY.
+  std::swap(mEvent.mDeltaX, mEvent.mDeltaY);
+  if (mOldDeltaX != mEvent.mDeltaX || mOldDeltaY != mEvent.mDeltaY) {
+    // If X and Y still don't equal to their original values after being
+    // swapped, then it must be because they were adjusted for RTL.
+    forRTL = true;
+    mEvent.mDeltaX *= -1;
+    mEvent.mDeltaY *= -1;
+    MOZ_ASSERT(mOldDeltaX == mEvent.mDeltaX && mOldDeltaY == mEvent.mDeltaY);
+  }
+
+  if (mEvent.mDeltaX) {
+    // A horizontal scroll was adjusted to be vertical during the lifetime of
+    // this instance.
+    MOZ_ASSERT(0 == mEvent.mDeltaY);
+
+    // Restore the line-or-page and overflow values to be horizontal.
+    mEvent.mOverflowDeltaX = mEvent.mOverflowDeltaY;
+    mEvent.mLineOrPageDeltaX = mEvent.mLineOrPageDeltaY;
+    if (forRTL) {
+      mEvent.mOverflowDeltaX *= -1;
+      mEvent.mLineOrPageDeltaX *= -1;
+    }
+    mEvent.mOverflowDeltaY = mOldOverflowDeltaY;
+    mEvent.mLineOrPageDeltaY = mOldLineOrPageDeltaY;
+  } else {
+    // A vertical scroll was adjusted to be horizontal during the lifetime of
+    // this instance.
+    MOZ_ASSERT(0 != mEvent.mDeltaY);
+
+    // Restore the line-or-page and overflow values to be vertical.
+    mEvent.mOverflowDeltaY = mEvent.mOverflowDeltaX;
+    mEvent.mLineOrPageDeltaY = mEvent.mLineOrPageDeltaX;
+    if (forRTL) {
+      mEvent.mOverflowDeltaY *= -1;
+      mEvent.mLineOrPageDeltaY *= -1;
+    }
+    mEvent.mOverflowDeltaX = mOldOverflowDeltaX;
+    mEvent.mLineOrPageDeltaX = mOldLineOrPageDeltaX;
+  }
+}
+
+}  // namespace mozilla
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