Qt5 has several changes that break the API-compatibility to Qt4. Especially the transition to the Lighthouse/QPA architecture makes it necessary to adjust KWin accordingly.

QPixmap/XPixmap

Problem Description

In Qt 5 QPixmap can no longer reference an xcb_pixmap_t, which means that it cannot be used as a backend for XRender compositing. Dangerous API calls are:

QPixmap::fromX11Pixmap
QPixmap::x11PictureHandle
QPixmap::handle

How to solve

The solution depends on the usage. If QPixmap has been used to simplify drawing (e.g. QPainter) the drawing commands need to be ported to low level xcb render API. If QPixmap has been used to limit memory copies and to simplify sharing with QImage it becomes more difficult. Sharing to a QImage needs to be implemented and ported to it. Areas where QPixmap is used to get e.g. the drawing of a widget to be used later on in compositing, can only be partially adjusted. The code can be written, but should not be used as for Qt 4 we should use the native graphics system for QPixmap in XRender backend as long as possible.

Problematic code areas

Status	Code Area	Problem
DONE	Screenshot Effect	window rendered into QPixmap, read into an image (http://commits.kde.org/kde-workspace/d593d6ef3675bc32e6d107fdb23e33dcc373f3a6 )
DONE	MouseClick Effect	drawing with QPainter on QPixmap (http://commits.kde.org/kde-workspace/e48b527981ac25f6304a6430f2b4af37169fb98a ) )
DONE	TrackMouse Effect	Image data loaded into QPixmap for rendering
DONE	PaintRedirector	QWidget drawing redirected into QPixmap
IN PROGRESS	Shadow	QPixmap for sharing data between windows
DONE	SceneXrender	QPixmap used as pixmap wrapper
DONE	EffectFrame	Usage of FrameSvg, provides QPixmap
DONE	kwinxrenderutils	Generating XRenderPicture from QPixmap
TODO	Client::icon	Icon is a QPixmap, needs to have QIcon and low level xcb_pixmap_t

QCursor

Problem Description

In Qt 5 QCursor does no longer expose the native handle, which means we cannot use it to manually setting the cursor with low level xcb calls.

How to solve

KWin needs it's own Cursor implementation (needed anyway for Wayland) which does both the low level interaction and providing an easy to use high level abstraction for internal usage.

Problematic code areas

Status	Code Area	Problem
DONE	Client::updateCursor	Used in XDefineCursor
DONE	EffectsHandlerImpl::createInputWindow	QCursor passed in to set the cursor image for the window
DONE	Cube Effect	QCursor used to update cursor on input window
DONE	DesktopGrid Effect	QCursor used to update cursor on input window
DONE	PresentWindows Effect	QCursor used to update cursor on input window
DONE	Client::startMoveResize	QCursor used to set the cursor while moving/resizing a window
DONE	Client::embedClient	Defined on window

QRegion

Problem Description

In Qt 5 QRegion no longer references a _XRegion which is used in conjunction with XShape.

How to solve

Code needs to be ported to XCB anyway which will replace the region by the rects.

Problematic code areas

Status	Code Area	Problem
DONE	Client::updateInputWindow()	http://commits.kde.org/kde-workspace/8dc1d43937b6ce6fdad79099ea399d459bcfe542
DONE	Client::setMask	http://commits.kde.org/kde-workspace/609d1b7953a46a8a12364b93be01b353f2fe0c1e
DONE	kcmdecoration KDecorationPreview::setPreviewMask	http://commits.kde.org/kde-workspace/1a6d15fe40688f3ccc06335fd5183f0ef941df1b
DONE	DecoBenchmark	http://commits.kde.org/kde-workspace/18059e67ee9d27cbf7a971e650803e926cb3f245

XEvent

Problem Description

The x11EventFilter from Qt 4 does no longer exist in Qt 5. The x11EventFilter provided an XEvent which could be passed through the application for processing. In Qt 5 there is the possibility to install a native event filter which receives xcb_generic_event_t.

How to solve

Main event processing needs to be split out into an own class which can in Qt 5 be derived from QAbstractNativeEventFilter. The logic for event filtering should be split into multiple methods which are as much as possible windowing system independent. E.g. if a mouse click is used it should operate on a QPoint and not on the native mouse press event. A complete port away from XEvent is not yet possible as with Qt 4 we won't get xcb_generic_event_t events through the event filter. Though it is a reasonable idea to add two parallel code pathes.

Problematic code areas

An InProgress here means that an xcb_generic_event_t method is added in addition to the XEvent method.

Status	Code Area	Problem
TODO	events.cpp	main event filter for KWin
TODO	Client::sendClientMessage	sends an XEvent to the Client
TODO	Client::sendSyncRequest()	sends an XEvent to the Client
TODO	EffectsHandlerImpl::checkInputWindowEvent	Input events for fullscreen effects
TODO	Client::sendSyntheticConfigureNotify	sends an XEvent to the Client
IN PROGRESS	KillWindow	own event handling
TODO	KWin::Application::Application()	sends an XEvent to update splash progress
TODO	Application::x11EventFilter	main filter passed to events.cpp
IN PROGRESS	ScreenEdge::isEntered	Checks notify enter events
TODO	TabBox::DeclarativeView::x11Event	Checks mouse events - only embedded mode
TODO	TabBox::handleMouseEvent	mouse events for TabBox
TODO	updateXTime()
TODO	update_x_time_predicate(..)