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/* -*- 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 */
#ifndef __mozilla_layers_AutoDirWheelDeltaAdjuster_h__
#define __mozilla_layers_AutoDirWheelDeltaAdjuster_h__
#include "Axis.h" // for AxisX, AxisY, Side
#include "mozilla/WheelHandlingHelper.h" // for AutoDirWheelDeltaAdjuster
namespace mozilla {
namespace layers {
* About AutoDirWheelDeltaAdjuster:
* For an AutoDir wheel scroll, there's some situations where we should adjust a
* wheel event's delta values. AutoDirWheelDeltaAdjuster converts delta values
* for AutoDir scrolling. An AutoDir wheel scroll lets the user scroll a frame
* with only one scrollbar, using either a vertical or a horzizontal wheel.
* For more detail about the concept of AutoDir scrolling, see the comments in
* AutoDirWheelDeltaAdjuster.
* This is the APZ implementation of AutoDirWheelDeltaAdjuster.
class MOZ_STACK_CLASS APZAutoDirWheelDeltaAdjuster final
: public AutoDirWheelDeltaAdjuster {
* @param aDeltaX DeltaX for a wheel event whose delta values will
* be adjusted upon calling adjust() when
* ShouldBeAdjusted() returns true.
* @param aDeltaY DeltaY for a wheel event, like DeltaX.
* @param aAxisX The X axis information provider for the current
* frame, such as whether the frame can be scrolled
* horizontally, leftwards or rightwards.
* @param aAxisY The Y axis information provider for the current
* frame, such as whether the frame can be scrolled
* vertically, upwards or downwards.
* @param aIsHorizontalContentRightToLeft
* Indicates whether the horizontal content starts
* at rightside. This value will decide which edge
* the adjusted scroll goes towards, in other words,
* it will decide the sign of the adjusted delta
* values). For detailed information, see
* IsHorizontalContentRightToLeft() in
* the base class AutoDirWheelDeltaAdjuster.
APZAutoDirWheelDeltaAdjuster(double& aDeltaX, double& aDeltaY,
const AxisX& aAxisX, const AxisY& aAxisY,
bool aIsHorizontalContentRightToLeft)
: AutoDirWheelDeltaAdjuster(aDeltaX, aDeltaY),
mIsHorizontalContentRightToLeft(aIsHorizontalContentRightToLeft) {}
virtual bool CanScrollAlongXAxis() const override {
return mAxisX.CanScroll();
virtual bool CanScrollAlongYAxis() const override {
return mAxisY.CanScroll();
virtual bool CanScrollUpwards() const override {
return mAxisY.CanScrollTo(eSideTop);
virtual bool CanScrollDownwards() const override {
return mAxisY.CanScrollTo(eSideBottom);
virtual bool CanScrollLeftwards() const override {
return mAxisX.CanScrollTo(eSideLeft);
virtual bool CanScrollRightwards() const override {
return mAxisX.CanScrollTo(eSideRight);
virtual bool IsHorizontalContentRightToLeft() const override {
return mIsHorizontalContentRightToLeft;
const AxisX& mAxisX;
const AxisY& mAxisY;
bool mIsHorizontalContentRightToLeft;
} // namespace layers
} // namespace mozilla
#endif // __mozilla_layers_AutoDirWheelDeltaAdjuster_h__