wheelhandler.h

/* SPDX-FileCopyrightText: 2019 Marco Martin <mart@kde.org>
 * SPDX-FileCopyrightText: 2021 Noah Davis <noahadvs@gmail.com>
 * SPDX-License-Identifier: LGPL-2.0-or-later
 */
 
#pragma once
 
#include <QGuiApplication>
#include <QObject>
#include <QPoint>
#include <QPropertyAnimation>
#include <QQmlParserStatus>
#include <QQuickItem>
#include <QStyleHints>
#include <QTimer>
 
#include "platform/settings.h"
#include "platform/units.h"
 
class QWheelEvent;
class QQmlEngine;
class WheelHandler;
 
/**
 * Describes the mouse wheel event
 */
class KirigamiWheelEvent : public QObject
{
    Q_OBJECT
    QML_ELEMENT
    QML_UNCREATABLE("")
 
    /**
     * x: real
     *
     * X coordinate of the mouse pointer
     */
    Q_PROPERTY(qreal x READ x CONSTANT FINAL)
 
    /**
     * y: real
     *
     * Y coordinate of the mouse pointer
     */
    Q_PROPERTY(qreal y READ y CONSTANT FINAL)
 
    /**
     * angleDelta: point
     *
     * The distance the wheel is rotated in degrees.
     * The x and y coordinates indicate the horizontal and vertical wheels respectively.
     * A positive value indicates it was rotated up/right, negative, bottom/left
     * This value is more likely to be set in traditional mice.
     */
    Q_PROPERTY(QPointF angleDelta READ angleDelta CONSTANT FINAL)
 
    /**
     * pixelDelta: point
     *
     * provides the delta in screen pixels available on high resolution trackpads
     */
    Q_PROPERTY(QPointF pixelDelta READ pixelDelta CONSTANT FINAL)
 
    /**
     * buttons: int
     *
     * it contains an OR combination of the buttons that were pressed during the wheel, they can be:
     * Qt.LeftButton, Qt.MiddleButton, Qt.RightButton
     */
    Q_PROPERTY(int buttons READ buttons CONSTANT FINAL)
 
    /**
     * modifiers: int
     *
     * Keyboard mobifiers that were pressed during the wheel event, such as:
     * Qt.NoModifier (default, no modifiers)
     * Qt.ControlModifier
     * Qt.ShiftModifier
     * ...
     */
    Q_PROPERTY(int modifiers READ modifiers CONSTANT FINAL)
 
    /**
     * inverted: bool
     *
     * Whether the delta values are inverted
     * On some platformsthe returned delta are inverted, so positive values would mean bottom/left
     */
    Q_PROPERTY(bool inverted READ inverted CONSTANT FINAL)
 
    /**
     * accepted: bool
     *
     * If set, the event shouldn't be managed anymore,
     * for instance it can be used to block the handler to manage the scroll of a view on some scenarios
     * @code
     * // This handler handles automatically the scroll of
     * // flickableItem, unless Ctrl is pressed, in this case the
     * // app has custom code to handle Ctrl+wheel zooming
     * Kirigami.WheelHandler {
     *   target: flickableItem
     *   blockTargetWheel: true
     *   scrollFlickableTarget: true
     *   onWheel: {
     *        if (wheel.modifiers & Qt.ControlModifier) {
     *            wheel.accepted = true;
     *            // Handle scaling of the view
     *       }
     *   }
     * }
     * @endcode
     *
     */
    Q_PROPERTY(bool accepted READ isAccepted WRITE setAccepted FINAL)
 
public:
    KirigamiWheelEvent(QObject *parent = nullptr);
    ~KirigamiWheelEvent() override;
 
    void initializeFromEvent(QWheelEvent *event);
 
    qreal x() const;
    qreal y() const;
    QPointF angleDelta() const;
    QPointF pixelDelta() const;
    int buttons() const;
    int modifiers() const;
    bool inverted() const;
    bool isAccepted();
    void setAccepted(bool accepted);
 
private:
    qreal m_x = 0;
    qreal m_y = 0;
    QPointF m_angleDelta;
    QPointF m_pixelDelta;
    Qt::MouseButtons m_buttons = Qt::NoButton;
    Qt::KeyboardModifiers m_modifiers = Qt::NoModifier;
    bool m_inverted = false;
    bool m_accepted = false;
};
 
class WheelFilterItem : public QQuickItem
{
    Q_OBJECT
public:
    WheelFilterItem(QQuickItem *parent = nullptr);
};
 
/**
 * @brief Handles scrolling for a Flickable and 2 attached ScrollBars.
 *
 * WheelHandler filters events from a Flickable, a vertical ScrollBar and a horizontal ScrollBar.
 * Wheel and KeyPress events (when `keyNavigationEnabled` is true) are used to scroll the Flickable.
 * When `filterMouseEvents` is true, WheelHandler blocks mouse button input from reaching the Flickable
 * and sets the `interactive` property of the scrollbars to false when touch input is used.
 *
 * Wheel event handling behavior:
 *
 * - Pixel delta is ignored unless angle delta is not available because pixel delta scrolling is too slow. Qt Widgets doesn't use pixel delta either, so the
 * default scroll speed should be consistent with Qt Widgets.
 * - When using angle delta, scroll using the step increments defined by `verticalStepSize` and `horizontalStepSize`.
 * - When one of the keyboard modifiers in `pageScrollModifiers` is used, scroll by pages.
 * - When using a device that doesn't use 120 angle delta unit increments such as a touchpad, the `verticalStepSize`, `horizontalStepSize` and page increments
 * (if using page scrolling) will be multiplied by `angle delta / 120` to keep scrolling smooth.
 * - If scrolling has happened in the last 400ms, use an internal QQuickItem stacked over the Flickable's contentItem to catch wheel events and use those wheel
 * events to scroll, if possible. This prevents controls inside the Flickable's contentItem that allow scrolling to change the value (e.g., Sliders, SpinBoxes)
 * from conflicting with scrolling the page.
 *
 * Common usage with a Flickable:
 *
 * @include wheelhandler/FlickableUsage.qml
 *
 * Common usage inside of a ScrollView template:
 *
 * @include wheelhandler/ScrollViewUsage.qml
 *
 */
class WheelHandler : public QObject, public QQmlParserStatus
{
    Q_OBJECT
    Q_INTERFACES(QQmlParserStatus)
    QML_ELEMENT
 
    /**
     * @brief This property holds the Qt Quick Flickable that the WheelHandler will control.
     */
    Q_PROPERTY(QQuickItem *target READ target WRITE setTarget NOTIFY targetChanged FINAL)
 
    /**
     * @brief This property holds the vertical step size.
     *
     * The default value is equivalent to `20 * Qt.styleHints.wheelScrollLines`. This is consistent with the default increment for QScrollArea.
     *
     * @sa horizontalStepSize
     *
     * @since KDE Frameworks 5.89
     */
    Q_PROPERTY(qreal verticalStepSize READ verticalStepSize WRITE setVerticalStepSize RESET resetVerticalStepSize NOTIFY verticalStepSizeChanged FINAL)
 
    /**
     * @brief This property holds the horizontal step size.
     *
     * The default value is equivalent to `20 * Qt.styleHints.wheelScrollLines`. This is consistent with the default increment for QScrollArea.
     *
     * @sa verticalStepSize
     *
     * @since KDE Frameworks 5.89
     */
    Q_PROPERTY(
        qreal horizontalStepSize READ horizontalStepSize WRITE setHorizontalStepSize RESET resetHorizontalStepSize NOTIFY horizontalStepSizeChanged FINAL)
 
    /**
     * @brief This property holds the keyboard modifiers that will be used to start page scrolling.
     *
     * The default value is equivalent to `Qt.ControlModifier | Qt.ShiftModifier`. This matches QScrollBar, which uses QAbstractSlider behavior.
     *
     * @since KDE Frameworks 5.89
     */
    Q_PROPERTY(Qt::KeyboardModifiers pageScrollModifiers READ pageScrollModifiers WRITE setPageScrollModifiers RESET resetPageScrollModifiers NOTIFY
                   pageScrollModifiersChanged FINAL)
 
    /**
     * @brief This property holds whether the WheelHandler filters mouse events like a Qt Quick Controls ScrollView would.
     *
     * Touch events are allowed to flick the view and they make the scrollbars not interactive.
     *
     * Mouse events are not allowed to flick the view and they make the scrollbars interactive.
     *
     * Hover events on the scrollbars and wheel events on anything also make the scrollbars interactive when this property is set to true.
     *
     * The default value is `false`.
     *
     * @since KDE Frameworks 5.89
     */
    Q_PROPERTY(bool filterMouseEvents READ filterMouseEvents WRITE setFilterMouseEvents NOTIFY filterMouseEventsChanged FINAL)
 
    /**
     * @brief This property holds whether the WheelHandler handles keyboard scrolling.
     *
     * - Left arrow scrolls a step to the left.
     * - Right arrow scrolls a step to the right.
     * - Up arrow scrolls a step upwards.
     * - Down arrow scrolls a step downwards.
     * - PageUp scrolls to the previous page.
     * - PageDown scrolls to the next page.
     * - Home scrolls to the beginning.
     * - End scrolls to the end.
     * - When Alt is held, scroll horizontally when using PageUp, PageDown, Home or End.
     *
     * The default value is `false`.
     *
     * @since KDE Frameworks 5.89
     */
    Q_PROPERTY(bool keyNavigationEnabled READ keyNavigationEnabled WRITE setKeyNavigationEnabled NOTIFY keyNavigationEnabledChanged FINAL)
 
    /**
     * @brief This property holds whether the WheelHandler blocks all wheel events from reaching the Flickable.
     *
     * When this property is false, scrolling the Flickable with WheelHandler will only block an event from reaching the Flickable if the Flickable is actually
     * scrolled by WheelHandler.
     *
     * NOTE: Wheel events created by touchpad gestures with pixel deltas will always be accepted no matter what. This is because they will cause the Flickable
     * to jump back to where scrolling started unless the events are always accepted before they reach the Flickable.
     *
     * The default value is true.
     */
    Q_PROPERTY(bool blockTargetWheel MEMBER m_blockTargetWheel NOTIFY blockTargetWheelChanged FINAL)
 
    /**
     * @brief This property holds whether the WheelHandler can use wheel events to scroll the Flickable.
     *
     * The default value is true.
     */
    Q_PROPERTY(bool scrollFlickableTarget MEMBER m_scrollFlickableTarget NOTIFY scrollFlickableTargetChanged FINAL)
 
public:
    explicit WheelHandler(QObject *parent = nullptr);
    ~WheelHandler() override;
 
    QQuickItem *target() const;
    void setTarget(QQuickItem *target);
 
    qreal verticalStepSize() const;
    void setVerticalStepSize(qreal stepSize);
    void resetVerticalStepSize();
 
    qreal horizontalStepSize() const;
    void setHorizontalStepSize(qreal stepSize);
    void resetHorizontalStepSize();
 
    Qt::KeyboardModifiers pageScrollModifiers() const;
    void setPageScrollModifiers(Qt::KeyboardModifiers modifiers);
    void resetPageScrollModifiers();
 
    bool filterMouseEvents() const;
    void setFilterMouseEvents(bool enabled);
 
    bool keyNavigationEnabled() const;
    void setKeyNavigationEnabled(bool enabled);
 
    /**
     * Scroll up one step. If the stepSize parameter is less than 0, the verticalStepSize will be used.
     *
     * returns true if the contentItem was moved.
     *
     * @since KDE Frameworks 5.89
     */
    Q_INVOKABLE bool scrollUp(qreal stepSize = -1);
 
    /**
     * Scroll down one step. If the stepSize parameter is less than 0, the verticalStepSize will be used.
     *
     * returns true if the contentItem was moved.
     *
     * @since KDE Frameworks 5.89
     */
    Q_INVOKABLE bool scrollDown(qreal stepSize = -1);
 
    /**
     * Scroll left one step. If the stepSize parameter is less than 0, the horizontalStepSize will be used.
     *
     * returns true if the contentItem was moved.
     *
     * @since KDE Frameworks 5.89
     */
    Q_INVOKABLE bool scrollLeft(qreal stepSize = -1);
 
    /**
     * Scroll right one step. If the stepSize parameter is less than 0, the horizontalStepSize will be used.
     *
     * returns true if the contentItem was moved.
     *
     * @since KDE Frameworks 5.89
     */
    Q_INVOKABLE bool scrollRight(qreal stepSize = -1);
 
Q_SIGNALS:
    void targetChanged();
    void verticalStepSizeChanged();
    void horizontalStepSizeChanged();
    void pageScrollModifiersChanged();
    void filterMouseEventsChanged();
    void keyNavigationEnabledChanged();
    void blockTargetWheelChanged();
    void scrollFlickableTargetChanged();
 
    /**
     * @brief This signal is emitted when a wheel event reaches the event filter, just before scrolling is handled.
     *
     * Accepting the wheel event in the `onWheel` signal handler prevents scrolling from happening.
     */
    void wheel(KirigamiWheelEvent *wheel);
 
protected:
    bool eventFilter(QObject *watched, QEvent *event) override;
 
private Q_SLOTS:
    void _k_rebindScrollBars();
 
private:
    void classBegin() override;
    void componentComplete() override;
    void initSmoothScrollDuration();
 
    void setScrolling(bool scrolling);
    bool scrollFlickable(QPointF pixelDelta, QPointF angleDelta = {}, Qt::KeyboardModifiers modifiers = Qt::NoModifier);
 
    Kirigami::Platform::Units *m_units = nullptr;
    Kirigami::Platform::Settings *m_settings = nullptr;
    QPointer<QQuickItem> m_flickable;
    QPointer<QQuickItem> m_verticalScrollBar;
    QPointer<QQuickItem> m_horizontalScrollBar;
    QMetaObject::Connection m_verticalChangedConnection;
    QMetaObject::Connection m_horizontalChangedConnection;
    QPointer<QQuickItem> m_filterItem;
    // Matches QScrollArea and QTextEdit
    qreal m_defaultPixelStepSize = 20 * QGuiApplication::styleHints()->wheelScrollLines();
    qreal m_verticalStepSize = m_defaultPixelStepSize;
    qreal m_horizontalStepSize = m_defaultPixelStepSize;
    bool m_explicitVStepSize = false;
    bool m_explicitHStepSize = false;
    bool m_wheelScrolling = false;
    constexpr static qreal m_wheelScrollingDuration = 400;
    bool m_filterMouseEvents = false;
    bool m_keyNavigationEnabled = false;
    bool m_blockTargetWheel = true;
    bool m_scrollFlickableTarget = true;
    // Same as QXcbWindow.
    constexpr static Qt::KeyboardModifiers m_defaultHorizontalScrollModifiers = Qt::AltModifier;
    // Same as QScrollBar/QAbstractSlider.
    constexpr static Qt::KeyboardModifiers m_defaultPageScrollModifiers = Qt::ControlModifier | Qt::ShiftModifier;
    Qt::KeyboardModifiers m_pageScrollModifiers = m_defaultPageScrollModifiers;
    QTimer m_wheelScrollingTimer;
    KirigamiWheelEvent m_kirigamiWheelEvent;
 
    // Smooth scrolling
    QQmlEngine *m_engine = nullptr;
    QPropertyAnimation m_yScrollAnimation{nullptr, "contentY"};
    bool m_wasTouched = false;
};