NOTE: this is not working completely yet, lots of code is still ifdefed
other parts are still broken.
The main difference for the new decoration API is that it is neither
QWidget nor QWindow based. It's just a QObject which processes input
events and has a paint method to render the decoration. This means all
the workarounds for the QWidget interception are removed. Also the paint
redirector is removed. Instead each compositor has now its own renderer
which can be optimized for the specific case. E.g. the OpenGL compositor
renders to a scratch image which gets copied into the combined texture,
the XRender compositor copies into the XPixmaps.
Input events are also changed. The events are composed into QMouseEvents
and passed through the decoration, which might accept them. If they are
not accpted we assume that it's a press on the decoration area allowing
us to resize/move the window. Input events are not completely working
yet, e.g. wheel events are not yet processed and double click on deco
is not yet working.
Overall KDecoration2 is way more stateful and KWin core needs more
adjustments for it. E.g. borders are allowed to be disabled at any time.
This compositor uses only the QPainter API to perform rendering. The
window's X Pixmap is mapped to a QImage using XShm. As rendering backend
a QImage is used.
The new compositing type "QPainterCompositing" is introduced. Effects
need to be adjusted to explicitly check the compositing type and no
longer assume the compositing type is XRender if it's not OpenGL.
This compositor can be selected with using "Q" as the value for
KWIN_COMPOSE env variable or setting the config value to "QPainter".
The GUI is not yet adjusted to select this compositor.
The QPainter scene provides currently the following features:
* 2D transformations (translation and scalation)
* opacity modifications
* rendering of decorations (new PaintRedirector sub class)
* rendering of shadows
* rendering of effect frames
* rendering to a Wayland surface
The following features are currently not provided:
* saturation changes
* brightness changes
* 3D transformations
* rendering to X Overlay window
* offscreen rendering (e.g. needed for screen shot effect)
* custom rendering in the effects to the current back buffer
