Currently, if a Wayland surface registers a frame callback but does
not send a damage event, the callback will not be serviced even after
KWin has completed a compositing cycle and is therefore ready to
render a new frame for the surface. Since some clients, including any
using NVIDIA's Wayland EGL implementation, wait for frame events
before preparing each frame this behavior can result in hangs if a
compositing cycle occurs between registering the frame callback and
sending the damage event.

Instead, in accordance with the Wayland specification, frame callbacks
should be serviced (via KWayland::Server::SurfaceInterface::frameRendered)
for all visible windows - not just those damaged since the last
compositing cycle.