Martin Gräßlin, one of the KDE developers that works on the KWin window manager, when not working towards OpenGL 3.0 support for KWin in KDE SC 4.7
has been writing a draft specification for what he proposes as a unified specification for compositing window managers. Martin hopes for this to become a FreeDesktop.org specification and that KWin/Plasma, Compiz, and other compositing window managers would implement this common specification.
Gräßlin would like this "Extended Compositing Manager Hints" specification to complement the FreeDesktop.org's existing Extended Window Manager Hints (EWMH) specification. The purpose of the ECMH specification would be that application developers could target this generic API for accessing compositing manager specifications and it would "just work" regardless of the compositing window manager in use -- or no effects in the case there is no compositing manager or that the effects are unavailable. Currently if an application developer wants to take advantage of any of these desktop effects, each and every compositing window manager must be targeted separately.
In this draft specification, the compositing effects mentioned include window previews, highlight windows, present windows, slide, dashboard, shadow, and blur.
Information on this proposed specification for compositing window managers can be found on the Compiz mailing list
with a link to the Extended Compositing Manager Hints draft.