qxcbxsettings.cpp

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// Copyright (C) 2016 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
 
#include "qxcbxsettings.h"
 
#include <QtCore/QByteArray>
#include <QtCore/QtEndian>
 
#include <vector>
#include <algorithm>
 
QT_BEGIN_NAMESPACE
/* Implementation of http://standards.freedesktop.org/xsettings-spec/xsettings-0.5.html */
 
enum XSettingsType {
    XSettingsTypeInteger = 0,
    XSettingsTypeString = 1,
    XSettingsTypeColor = 2
};
 
struct QXcbXSettingsCallback
{
    QXcbXSettings::PropertyChangeFunc func;
    void *handle;
};
 
class QXcbXSettingsPropertyValue
{
public:
    QXcbXSettingsPropertyValue()
        : last_change_serial(-1)
    {}
 
    void updateValue(QXcbVirtualDesktop *screen, const QByteArray &name, const QVariant &value, int last_change_serial)
    {
        if (last_change_serial <= this->last_change_serial)
            return;
        this->value = value;
        this->last_change_serial = last_change_serial;
        for (const auto &callback : callback_links)
            callback.func(screen, name, value, callback.handle);
    }
 
    void addCallback(QXcbXSettings::PropertyChangeFunc func, void *handle)
    {
        QXcbXSettingsCallback callback = { func, handle };
        callback_links.push_back(callback);
    }
 
    QVariant value;
    int last_change_serial;
    std::vector<QXcbXSettingsCallback> callback_links;
 
};
 
class QXcbXSettingsPrivate
{
public:
    QXcbXSettingsPrivate(QXcbVirtualDesktop *screen)
        : screen(screen)
        , initialized(false)
    {
    }
 
    QByteArray getSettings()
    {
        QXcbConnectionGrabber connectionGrabber(screen->connection());
 
        int offset = 0;
        QByteArray settings;
        xcb_atom_t _xsettings_atom = screen->connection()->atom(QXcbAtom::Atom_XSETTINGS_SETTINGS);
        while (1) {
            auto reply = Q_XCB_REPLY_UNCHECKED(xcb_get_property,
                                               screen->xcb_connection(),
                                               false,
                                               x_settings_window,
                                               _xsettings_atom,
                                               _xsettings_atom,
                                               offset/4,
                                               8192);
            bool more = false;
            if (!reply)
                return settings;
 
            const auto property_value_length = xcb_get_property_value_length(reply.get());
            settings.append(static_cast<const char *>(xcb_get_property_value(reply.get())), property_value_length);
            offset += property_value_length;
            more = reply->bytes_after != 0;
 
            if (!more)
                break;
        }
 
        return settings;
    }
 
    static int round_to_nearest_multiple_of_4(int value)
    {
        int remainder = value % 4;
        if (!remainder)
            return value;
        return value + 4 - remainder;
    }
 
    void populateSettings(const QByteArray &xSettings)
    {
        if (xSettings.size() < 12)
            return;
        char byteOrder = xSettings.at(0);
        if (byteOrder != XCB_IMAGE_ORDER_LSB_FIRST && byteOrder != XCB_IMAGE_ORDER_MSB_FIRST) {
            qWarning("ByteOrder byte %d not 0 or 1", byteOrder);
            return;
        }
 
#define ADJUST_BO(b, t, x) \
        ((b == XCB_IMAGE_ORDER_LSB_FIRST) ?                          \
         qFromLittleEndian<t>(x) : \
         qFromBigEndian<t>(x))
#define VALIDATE_LENGTH(x)    \
        if ((size_t)xSettings.length() < (offset + local_offset + 12 + x)) { \
            qWarning("Length %d runs past end of data", x); \
            return;                                                     \
        }
 
        uint number_of_settings = ADJUST_BO(byteOrder, quint32, xSettings.mid(8,4).constData());
        const char *data = xSettings.constData() + 12;
        size_t offset = 0;
        for (uint i = 0; i < number_of_settings; i++) {
            int local_offset = 0;
            VALIDATE_LENGTH(2);
            XSettingsType type = static_cast<XSettingsType>(*reinterpret_cast<const quint8 *>(data + offset));
            local_offset += 2;
 
            VALIDATE_LENGTH(2);
            quint16 name_len = ADJUST_BO(byteOrder, quint16, data + offset + local_offset);
            local_offset += 2;
 
            VALIDATE_LENGTH(name_len);
            QByteArray name(data + offset + local_offset, name_len);
            local_offset += round_to_nearest_multiple_of_4(name_len);
 
            VALIDATE_LENGTH(4);
            int last_change_serial = ADJUST_BO(byteOrder, qint32, data + offset + local_offset);
            Q_UNUSED(last_change_serial);
            local_offset += 4;
 
            QVariant value;
            if (type == XSettingsTypeString) {
                VALIDATE_LENGTH(4);
                int value_length = ADJUST_BO(byteOrder, qint32, data + offset + local_offset);
                local_offset+=4;
                VALIDATE_LENGTH(value_length);
                QByteArray value_string(data + offset + local_offset, value_length);
                value.setValue(value_string);
                local_offset += round_to_nearest_multiple_of_4(value_length);
            } else if (type == XSettingsTypeInteger) {
                VALIDATE_LENGTH(4);
                int value_length = ADJUST_BO(byteOrder, qint32, data + offset + local_offset);
                local_offset += 4;
                value.setValue(value_length);
            } else if (type == XSettingsTypeColor) {
                VALIDATE_LENGTH(2*4);
                quint16 red = ADJUST_BO(byteOrder, quint16, data + offset + local_offset);
                local_offset += 2;
                quint16 green = ADJUST_BO(byteOrder, quint16, data + offset + local_offset);
                local_offset += 2;
                quint16 blue = ADJUST_BO(byteOrder, quint16, data + offset + local_offset);
                local_offset += 2;
                quint16 alpha= ADJUST_BO(byteOrder, quint16, data + offset + local_offset);
                local_offset += 2;
                QColor color_value(red,green,blue,alpha);
                value.setValue(color_value);
            }
            offset += local_offset;
            settings[name].updateValue(screen,name,value,last_change_serial);
        }
 
    }
 
    QXcbVirtualDesktop *screen;
    xcb_window_t x_settings_window;
    QMap<QByteArray, QXcbXSettingsPropertyValue> settings;
    bool initialized;
};
 
 
QXcbXSettings::QXcbXSettings(QXcbVirtualDesktop *screen)
    : d_ptr(new QXcbXSettingsPrivate(screen))
{
    QByteArray settings_atom_for_screen("_XSETTINGS_S");
    settings_atom_for_screen.append(QByteArray::number(screen->number()));
    auto atom_reply = Q_XCB_REPLY(xcb_intern_atom,
                                  screen->xcb_connection(),
                                  true,
                                  settings_atom_for_screen.size(),
                                  settings_atom_for_screen.constData());
    if (!atom_reply)
        return;
 
    xcb_atom_t selection_owner_atom = atom_reply->atom;
 
    xcb_window_t owner = screen->connection()->selectionOwner(selection_owner_atom);
    if (owner == XCB_NONE)
        return;
 
    d_ptr->x_settings_window = owner;
    if (!d_ptr->x_settings_window)
        return;
 
    screen->connection()->addWindowEventListener(d_ptr->x_settings_window, this);
    const uint32_t event = XCB_CW_EVENT_MASK;
    const uint32_t event_mask[] = { XCB_EVENT_MASK_STRUCTURE_NOTIFY|XCB_EVENT_MASK_PROPERTY_CHANGE };
    xcb_change_window_attributes(screen->xcb_connection(),d_ptr->x_settings_window,event,event_mask);
 
    d_ptr->populateSettings(d_ptr->getSettings());
    d_ptr->initialized = true;
}
 
QXcbXSettings::~QXcbXSettings()
{
    delete d_ptr;
    d_ptr = nullptr;
}
 
bool QXcbXSettings::initialized() const
{
    Q_D(const QXcbXSettings);
    return d->initialized;
}
 
void QXcbXSettings::handlePropertyNotifyEvent(const xcb_property_notify_event_t *event)
{
    Q_D(QXcbXSettings);
    if (event->window != d->x_settings_window)
        return;
 
    d->populateSettings(d->getSettings());
}
 
void QXcbXSettings::registerCallbackForProperty(const QByteArray &property, QXcbXSettings::PropertyChangeFunc func, void *handle)
{
    Q_D(QXcbXSettings);
    d->settings[property].addCallback(func,handle);
}
 
void QXcbXSettings::removeCallbackForHandle(const QByteArray &property, void *handle)
{
    Q_D(QXcbXSettings);
    auto &callbacks = d->settings[property].callback_links;
 
    auto isCallbackForHandle = [handle](const QXcbXSettingsCallback &cb) { return cb.handle == handle; };
 
    callbacks.erase(std::remove_if(callbacks.begin(), callbacks.end(),
                                   isCallbackForHandle),
                    callbacks.end());
}
 
void QXcbXSettings::removeCallbackForHandle(void *handle)
{
    Q_D(QXcbXSettings);
    for (QMap<QByteArray, QXcbXSettingsPropertyValue>::const_iterator it = d->settings.cbegin();
         it != d->settings.cend(); ++it) {
        removeCallbackForHandle(it.key(),handle);
    }
}
 
QVariant QXcbXSettings::setting(const QByteArray &property) const
{
    Q_D(const QXcbXSettings);
    return d->settings.value(property).value;
}
 
QT_END_NAMESPACE