Plasma/shellswitching

definitions

shell: the binary that loads full screen and displays desktop, panels, etc. currently those would be: plasma-desktop, plasma-netbook, plasma-device, etc.
workspace: a full arrangement of shell (+ default layout), window manager, GUI utilities (e.g. krunner) and infrastructure processes (kactivitymanagerd, e.g.)

Workspaces should be defined by self-contained Plasma Packages, one per workspace setup, containing:

processes other than the shell and window manager that are required (e.g. krunner, software keyboard)
QML layout to use (perhaps also included in package?)
kwin configuration
other application configuration (krunner, e.g.?)

What is the current workspace will be tracked by a kded module. Features:

auto-switching based on triggers.
- screen change
- docking
- custom user signal?
manual switching via dbus (perhaps tied to window manager; see secdtion on kwin)
dbus signal emitted when workspace changes
- shell may load a different QML layout
- kwin may change settings
start/stop processes according to workspace definition.
- e.g. "desktop" will want to start krunner; switching to "netbook" which does not include krunner in its definition would result in krunner being stopped
- re-use session management for this? some custom configuration system? modified startactive? systemd? or ...?

All the shells will be replaced by an upgraded plasma-device.

control UI (add widgets, e.g.) will move into the shell QML, just as it is with plasma-device now in Plasma Active.
- for desktop that includes: activity switcher, add widgets, panel settings
will listen to the workspace change signal from the kded module and possibly load a different workspace QML structure
the following features from plasma-desktop must be ported:
- multiple panels
- multi-screen awareness
- integrate Desktop Scripting (perhaps even becoming the way layouts are set up)
a single DBus API will need to be settled on (alternative is allowing each shell layout to define a custom one; technically more difficult and the benefit is undefined)

still largely TBD ...

will need to contain:

Creates a QQuickView subclass (View, in the shell and not in libplasma anymore) for each screen (using qdesktopwidget)
Loads a qml file coming from a package for each view (same role as contour-himescreen in plasma-device)
When a containment gains a screen, a pointer to the root object of the containment qml package needs to be accessible: it will become child of the view qml file (this will also make possible to perform transition animations)
Same thing will be needed for panels
Pieces of plasma-devices and plsma-desktop shell will be transplanted there (or whatever final repository will be) until the features are complete. Note: some features, such full support for activities are blocked by the full port of other components (kactivities, nepomuk-core)

kwin will need to be able to source different sets of configuration files and change it's configuration in response to the signal
an elegant desktop effect to make the workspace UI reshuffle smooth
- a simple fade to black with a busy spinner , followed by a fade back in would be enough
- requires that kwin is the first process that starts switching
- requires that kwin controls when the change signal is emitted to other processes
- requires that applications provide feedback as to when they are finished transforming to trigger the fade in
- unload/load window decoration, currently either a decoration is required (desktop) or hard disabled in code (active)

would be fantastic if applications can also adjust; e.g. okular switch from desktop to touch UI on workspace change.