qquicksafearea.cpp

Go to the documentation of this file.

// Copyright (C) 2024 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
// Qt-Security score:significant reason:default
 
#include <QtQuick/private/qquicksafearea_p.h>
 
#include <QtQuick/private/qquickanchors_p_p.h>
#include <QtQuick/private/qquickitem_p.h>
#include <QtQuick/private/qquickflickable_p.h>
#include <QtQuick/qquickwindow.h>
#include <QtQuick/qquickitem.h>
 
QT_BEGIN_NAMESPACE
 
Q_STATIC_LOGGING_CATEGORY(lcSafeArea, "qt.quick.safearea", QtWarningMsg)
 
/*!
    \qmltype SafeArea
    \nativetype QQuickSafeArea
    \inqmlmodule QtQuick
    \ingroup qtquick-visual
    \since 6.9
    \brief Provides access to the safe area properties of the item or window.
 
    The SafeArea attached type provides information about the areas of
    an Item or Window where content may risk being overlapped by other
    UI elements, such as system title bars or status bars.
 
    This information can be used to lay out children of an item within
    the safe area of the item, while still allowing a background color
    or effect to span the entire item.
 
    \table
    \row
      \li \snippet qml/safearea/basic.qml 0
      \li \inlineimage safearea-ios.webp
    \endtable
 
    The SafeArea margins are relative to the item they attach to. If an
    ancestor item has laid out its children within the safe area margins,
    any descendant item with its own SafeArea attached will report zero
    margins, unless \l{Additional margins}{additional margins} have been
    added.
 
    \note An item should not be positioned based on \e{its own} safe area,
    as that would result in a binding loop.
 
    \section2 Additional margins
 
    Sometimes an item's layout involves child items that overlap each other,
    for example in a window with a semi transparent header, where the rest
    of the window content flows underneath the header.
 
    In this scenario, the item may reflect the header's position and size
    to the child items via the additionalMargins property.
 
    The additional margins will be added to any margins that the
    item already picks up from its parent hierarchy (including system
    margins, such as title bars or status bars), and child items will
    reflect the combined margins accordingly.
 
    \table
    \row
      \li \snippet qml/safearea/additional.qml 0
      \li \br \inlineimage safearea-ios-header.webp
    \endtable
 
    In the example above, the header item is positioned at the top of
    the window, which may potentially overlap with existing safe area
    margins coming from the window. To account for this we only add
    additional margins for the part of the header that extends beyond
    the window's safe area margins.
 
    \note In this example the header item does not overlap the child item,
    as the goal is to show how the items are positioned and resized in
    response to safe area margin changes.
 
    \section2 Controls
 
    Applying safe area margins to a Control is straightforward,
    as Control already offers properties to add padding to the
    control's content item.
 
    \snippet qml/safearea/controls.qml 0
 */
 
QQuickSafeArea *QQuickSafeArea::qmlAttachedProperties(QObject *attachee)
{
    auto *item = qobject_cast<QQuickItem*>(attachee);
    if (!item) {
        if (auto *window = qobject_cast<QQuickWindow*>(attachee))
            item = window->contentItem();
    }
    if (!item) {
        if (auto *safeAreaAttachable = qobject_cast<QQuickSafeAreaAttachable*>(attachee))
            item = safeAreaAttachable->safeAreaAttachmentItem();
    }
    if (!item) {
        qmlWarning(attachee) << "SafeArea can not be attached to this type";
        return nullptr;
    }
 
    // We may already have created a safe area for Window, and are now
    // requesting one for Window.contentItem (or the other way around).
    // As both map to the same safe area item, we need to check first
    // if we already have created one for this item.
    if (auto *safeArea = item->findChild<QQuickSafeArea*>(Qt::FindDirectChildrenOnly))
        return safeArea;
 
    return new QQuickSafeArea(item);
}
 
QQuickSafeArea::QQuickSafeArea(QQuickItem *item)
    : QObject(item)
{
    qCInfo(lcSafeArea) << "Creating" << this;
 
    connect(item, &QQuickItem::windowChanged,
            this, &QQuickSafeArea::windowChanged);
 
    item->setFlag(QQuickItem::ItemObservesViewport);
    QQuickItemPrivate::get(item)->addItemChangeListener(
        this, QQuickItemPrivate::Matrix);
 
    updateSafeArea();
}
 
QQuickSafeArea::~QQuickSafeArea()
{
    qCInfo(lcSafeArea) << "Destroying" << this;
 
    const auto listenedItems = m_listenedItems;
    for (const auto &item : listenedItems) {
        if (!item)
            continue;
        auto *itemPrivate = QQuickItemPrivate::get(item);
        itemPrivate->removeItemChangeListener(this,
            QQuickItemPrivate::Matrix);
        itemPrivate->removeItemChangeListener(this,
            QQuickItemPrivate::Geometry);
    }
}
 
/*!
    \qmlpropertygroup QtQuick::SafeArea::margins
    \qmlproperty real QtQuick::SafeArea::margins.top
    \qmlproperty real QtQuick::SafeArea::margins.left
    \qmlproperty real QtQuick::SafeArea::margins.right
    \qmlproperty real QtQuick::SafeArea::margins.bottom
    \readonly
 
    This property holds the safe area margins, relative
    to the attached item.
 
    \sa additionalMargins
 */
QMarginsF QQuickSafeArea::margins() const
{
    return m_safeAreaMargins;
}
 
/*!
    \qmlpropertygroup QtQuick::SafeArea::additionalMargins
    \qmlproperty real QtQuick::SafeArea::additionalMargins.top
    \qmlproperty real QtQuick::SafeArea::additionalMargins.left
    \qmlproperty real QtQuick::SafeArea::additionalMargins.right
    \qmlproperty real QtQuick::SafeArea::additionalMargins.bottom
 
    This property holds the additional safe area margins for the item.
 
    The additional safe area margins can not be negative, and will be
    automatically clamped to 0.
 
    The resulting safe area margins of the item are the sum of the inherited
    margins (for example from title bars or status bar) and the additional
    margins applied to the item.
 
    \sa margins
 */
 
void QQuickSafeArea::setAdditionalMargins(const QMarginsF &additionalMargins)
{
    // Additional margins should never be negative
    auto newMargins = additionalMargins | QMarginsF();
 
    if (newMargins == m_additionalMargins)
        return;
 
    m_additionalMargins = newMargins;
 
    emit additionalMarginsChanged();
 
    auto *attachedItem = qobject_cast<QQuickItem*>(parent());
    updateSafeAreasRecursively(attachedItem);
}
 
QMarginsF QQuickSafeArea::additionalMargins() const
{
    return m_additionalMargins;
}
 
/*
    Maps the safe area \a margins from \a fromItem to \a toItem
*/
static QMarginsF toLocalMargins(const QMarginsF &margins, QQuickItem *fromItem, QQuickItem *toItem)
{
    if (margins.isNull())
        return margins;
 
    const auto localMarginRect = fromItem->mapRectToItem(toItem,
        QRectF(margins.left(), margins.top(),
               fromItem->width() - margins.left() - margins.right(),
               fromItem->height() - margins.top() - margins.bottom()));
 
    // Only return a mapped margin if there was an original margin
    return QMarginsF(
        margins.left() > 0 ? localMarginRect.left() : 0,
        margins.top() > 0 ? localMarginRect.top() : 0,
        margins.right() > 0 ? toItem->width() - localMarginRect.right() : 0,
        margins.bottom() > 0 ? toItem->height() - localMarginRect.bottom() : 0
    ) | QMarginsF();
}
 
void QQuickSafeArea::updateSafeArea()
{
    qCDebug(lcSafeArea) << "✨ Updating" << this;
 
    auto *attachedItem = qobject_cast<QQuickItem*>(parent());
    if (!QQuickItemPrivate::get(attachedItem)->componentComplete) {
        qCDebug(lcSafeArea) << attachedItem << "is not complete. Deferring";
        return;
    }
 
    QMarginsF inheritedMargins;
    auto *parentItem = attachedItem->parentItem();
    while (parentItem) {
        if (qobject_cast<QQuickFlickable*>(parentItem)) {
            // Stop propagation of safe areas when we hit a Flickable,
            // as items within the content item that account for safe
            // area margins will continuously update when the content
            // item is moved, which is not necessarily what the user
            // expects.
            qCDebug(lcSafeArea) << "Stopping safe area margin propagation on" << parentItem;
            break;
        }
 
 
        // We attach the safe area to the relevant item for an attachee
        // such as QQuickWindow or QQuickPopup, so we can't go via
        // qmlAttachedPropertiesObject to find the safe area for an
        // item, as the attached object cache is based on the original
        // attachee.
        if (auto *safeArea = parentItem->findChild<QQuickSafeArea*>(Qt::FindDirectChildrenOnly)) {
            inheritedMargins = safeArea->margins();
            break;
        }
 
        parentItem = parentItem->parentItem();
    }
 
    const auto *window = attachedItem->window();
    if (!parentItem && window) {
        // We didn't find a parent item with a safe area,
        // so inherit the margins from the window.
        parentItem = window->contentItem();
        inheritedMargins = window->safeAreaMargins();
    }
 
    auto inheritedMarginsMapped = toLocalMargins(inheritedMargins, parentItem, attachedItem);
 
    // Make sure margins are never negative
    const QMarginsF newMargins = QMarginsF() | (inheritedMarginsMapped + additionalMargins());
 
    if (newMargins != m_safeAreaMargins) {
        qCDebug(lcSafeArea) << "Margins changed from" << m_safeAreaMargins
            << "to" << newMargins
            << "based on inherited" << inheritedMargins
            << "mapped to local" << inheritedMarginsMapped
            << "and additional" << additionalMargins();
 
        m_safeAreaMargins = newMargins;
 
        if (emittingMarginsUpdate) {
            // We are already in the process of emitting an update for this
            // safe area, which resulted in the safe area margins changing.
            // This can be a binding loop if the margins do not stabilize,
            // which we'll detect when we return from the root emit below.
            qCDebug(lcSafeArea) << "Already emitting update for" << this;
            return;
        }
 
        QScopedValueRollback blocker(emittingMarginsUpdate, true);
        emit marginsChanged();
 
        if (m_safeAreaMargins != newMargins) {
            qCDebug(lcSafeArea) << "⚠️ Possible binding loop for" << this
                << newMargins << "changed to" << m_safeAreaMargins;
 
            QScopedValueRollback blocker(detectedPossibleBindingLoop, true);
 
            for (int i = 0; i < 5; ++i) {
                auto marginsBeforeEmit = m_safeAreaMargins;
                emit marginsChanged();
                if (m_safeAreaMargins == marginsBeforeEmit) {
                    qCDebug(lcSafeArea) << "✅ Margins stabilized for" << this;
                    return;
                }
 
                qCDebug(lcSafeArea) << qPrintable(QStringLiteral("‼️").repeated(i + 1))
                    << marginsBeforeEmit << "changed to" << m_safeAreaMargins;
            }
 
            qmlWarning(attachedItem) << "Safe area binding loop detected";
        }
    }
}
 
void QQuickSafeArea::windowChanged()
{
    updateSafeArea();
}
 
void QQuickSafeArea::itemTransformChanged(QQuickItem *item, QQuickItem *transformedItem)
{
    Q_ASSERT(item == parent());
 
    auto *transformedItemPrivate = QQuickItemPrivate::get(transformedItem);
    qCDebug(lcSafeArea) << "📏 Transform changed for" << transformedItem
                        << "with dirty state" << transformedItemPrivate->dirtyToString();
 
    if (qobject_cast<QQuickFlickable*>(transformedItem->parentItem())) {
        qCDebug(lcSafeArea) << "Ignoring transform change for Flickable content item";
        return;
    }
 
    // The order of transform and geometry change callbacks may not be in paint order,
    // so to ensure we update the safe areas in paint order we find the item closest
    // to the transformed item with a safe area, and let that safe area trigger the
    // update recursively in paint order.
    if (transformedItem != item) {
        for (auto *parent = item->parentItem(); parent; parent = parent->parentItem()) {
            if (parent->findChild<QQuickSafeArea*>(Qt::FindDirectChildrenOnly))
                item = parent;
 
            if (parent == transformedItem)
                break;
        }
    }
 
    if (item != parent()) {
        qCDebug(lcSafeArea) << "Found" << item << "closer to transformed item than" << this;
        return;
    }
 
    // The dirtying of position and size will be followed by a geometry change,
    // which via anchors or event listeners may result in an ancestor invalidating
    // its transform, which might invalidate the margins we're about to compute.
    // Instead of processing the margin change now, possibly resulting in a flip-
    // flop of the margins, we wait for the geometry notification, where the item
    // hierarchy has already reacted to the geometry change of the transformed item.
    // This accounts for anchors, and items that listen to geometry changes, but not
    // property bindings, as those are emitted after notifying listeners (us) about
    // the geometry change.
    auto dirtyAttributes = transformedItemPrivate->dirtyAttributes;
    if (dirtyAttributes & (QQuickItemPrivate::Position | QQuickItemPrivate::Size)) {
        qCDebug(lcSafeArea) << "Deferring update of" << this << "until geometry change";
        transformedItemPrivate->addItemChangeListener(
            this, QQuickItemPrivate::Geometry);
        return;
    }
 
    updateSafeAreasRecursively(item);
}
 
void QQuickSafeArea::itemGeometryChanged(QQuickItem *item, QQuickGeometryChange change, const QRectF &oldGeometry)
{
    Q_UNUSED(change);
    Q_UNUSED(oldGeometry);
 
    auto *itemPrivate = QQuickItemPrivate::get(item);
    itemPrivate->removeItemChangeListener(this, QQuickItemPrivate::Geometry);
 
    qCDebug(lcSafeArea) << "📐 Geometry changed for" << item << "from" << oldGeometry
                        << "to" << QRectF(item->position(), item->size());
 
    updateSafeAreasRecursively(item);
}
 
void QQuickSafeArea::updateSafeAreasRecursively(QQuickItem *item)
{
    Q_ASSERT(item);
 
    if (auto *safeArea = item->findChild<QQuickSafeArea*>(Qt::FindDirectChildrenOnly))
        safeArea->updateSafeArea();
 
    auto *itemPrivate = QQuickItemPrivate::get(item);
    const auto paintOrderChildItems = itemPrivate->paintOrderChildItems();
    for (auto *child : paintOrderChildItems)
        updateSafeAreasRecursively(child);
}
 
void QQuickSafeArea::addSourceItem(QQuickItem *item)
{
    m_listenedItems << item;
}
 
void QQuickSafeArea::removeSourceItem(QQuickItem *item)
{
    m_listenedItems.removeAll(item);
}
 
#ifndef QT_NO_DEBUG_STREAM
QDebug operator<<(QDebug debug, const QQuickSafeArea *safeArea)
{
    QDebugStateSaver saver(debug);
    debug.nospace();
 
    if (!safeArea) {
        debug << "QQuickSafeArea(nullptr)";
        return debug;
    }
 
    debug << safeArea->metaObject()->className() << '(' << static_cast<const void *>(safeArea);
 
    debug << ", attachedItem=" << safeArea->parent();
    debug << ", safeAreaMargins=" << safeArea->m_safeAreaMargins;
    debug << ", additionalMargins=" << safeArea->additionalMargins();
 
    debug << ')';
    return debug;
}
#endif // QT_NO_DEBUG_STREAM
 
QQuickSafeAreaAttachable::~QQuickSafeAreaAttachable() = default;
 
QT_END_NAMESPACE
 
#include "moc_qquicksafearea_p.cpp"