A `GdkFrameClock` tells the application when to update and repaint a surface.
This may be synced to the vertical refresh rate of the monitor, for example. Even when the frame clock uses a simple timer rather than a
hardware-based vertical sync, the frame clock helps because it ensures everything paints at the same time (reducing the total number of
frames).
The frame clock can also automatically stop painting when it knows the frames will not be visible, or scale back animation framerates.
`GdkFrameClock` is designed to be compatible with an OpenGL-based implementation or with mozRequestAnimationFrame in Firefox, for
example.
A frame clock is idle until someone requests a frame with [[email protected]_phase]. At some later point that makes sense for
the synchronization being implemented, the clock will process a frame and emit signals for each phase that has been requested. (See the
signals of the `GdkFrameClock` class for documentation of the phases. gdk_frame_clock_phase_update and
the [signal@GdkFrameClock:GdkFrameClock:update] signal are most interesting for application writers, and are used to update
the animations, using the frame time given by [[email protected]_frame_time].
The frame time is reported in microseconds and generally in the same timescale as get_monotonic_time,
however, it is not the same as get_monotonic_time. The frame time does not advance during the time a frame is
being painted, and outside of a frame, an attempt is made so that all calls to [[email protected]_frame_time] that are called at a
“similar” time get the same value. This means that if different animations are timed by looking at the difference in time between an
initial value from [[email protected]_frame_time] and the value inside the [signal@GdkFrameClock:GdkFrameClock:update
] signal of the clock, they will stay exactly synchronized.