ge_event_mem_mover.h

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/*
    KWin - the KDE window manager
    This file is part of the KDE project.
 
    SPDX-FileCopyrightText: 2018 Martin Flöser <mgraesslin@kde.org>
 
    SPDX-License-Identifier: GPL-2.0-or-later
*/
#pragma once
 
#include <xcb/xcb.h>
 
#include <cstring>
 
namespace KWin
{
 
class GeEventMemMover
{
public:
    GeEventMemMover(xcb_generic_event_t *event)
        : m_event(reinterpret_cast<xcb_ge_generic_event_t *>(event))
    {
        // xcb event structs contain stuff that wasn't on the wire, the full_sequence field
        // adds an extra 4 bytes and generic events cookie data is on the wire right after the standard 32 bytes.
        // Move this data back to have the same layout in memory as it was on the wire
        // and allow casting, overwriting the full_sequence field.
        memmove((char *)m_event + 32, (char *)m_event + 36, m_event->length * 4);
    }
    ~GeEventMemMover()
    {
        // move memory layout back, so that Qt can do the same without breaking
        memmove((char *)m_event + 36, (char *)m_event + 32, m_event->length * 4);
    }
 
    xcb_ge_generic_event_t *operator->() const
    {
        return m_event;
    }
 
private:
    xcb_ge_generic_event_t *m_event;
};
 
}