GCC has some optimization for the inclusion guard, but they only work if
the check is the outermost one.
We're fairly inconsistent because of historical reasons, so we should
ensure that we follow the same pattern in every public header.
A long press is a special form of click action; the default
implementation uses a single signal with multiple states: query, action
and cancel. On click we use the "query" state to check whether the
ClutterClickAction supports long presses; if the callback returns TRUE
then we install a timeout and we either emit the "activate" state when
the timeout expires or we emit the "cancel" state if the pointer leaves
the actor, or if the pointer moves outside a certain threshold. If the
long press reached the "activate" state then we skip the clicked signal
emission.
It can be useful to be able to forcibly break the grab set up by the
ClickAction. The newly added release() method provides a mechanism to
release the grab and unset the :held state of the ClickAction.
ClickAction adds "clickable" semantics to an actor. It provides all
the business logic to emit a high-level "clicked" signal from the
various low-level signals inside ClutterActor.
