FrameClock
Superclasses: Object
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
request_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.
UPDATE
and the update
signal
are most interesting for application writers, and are used to update the
animations, using the frame time given by get_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 get_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 get_frame_time
and the value inside the update
signal of the clock,
they will stay exactly synchronized.
Methods
- class FrameClock
- begin_updating() None
Starts updates for an animation.
Until a matching call to
end_updating
is made, the frame clock will continually request a new frame with theUPDATE
phase. This function may be called multiple times and frames will be requested untilend_updating()
is called the same number of times.
- end_updating() None
Stops updates for an animation.
See the documentation for
begin_updating
.
- get_current_timings() FrameTimings | None
Gets the frame timings for the current frame.
- get_fps() float
Calculates the current frames-per-second, based on the frame timings of
frame_clock
.
- get_frame_counter() int
GdkFrameClock
maintains a 64-bit counter that increments for each frame drawn.
- get_frame_time() int
Gets the time that should currently be used for animations.
Inside the processing of a frame, it’s the time used to compute the animation position of everything in a frame. Outside of a frame, it’s the time of the conceptual “previous frame,” which may be either the actual previous frame time, or if that’s too old, an updated time.
- get_history_start() int
Returns the frame counter for the oldest frame available in history.
GdkFrameClock
internally keeps a history ofGdkFrameTimings
objects for recent frames that can be retrieved withget_timings
. The set of stored frames is the set from the counter values given byget_history_start
andget_frame_counter
, inclusive.
- get_refresh_info(base_time: int) tuple[int, int]
Predicts a presentation time, based on history.
Using the frame history stored in the frame clock, finds the last known presentation time and refresh interval, and assuming that presentation times are separated by the refresh interval, predicts a presentation time that is a multiple of the refresh interval after the last presentation time, and later than
base_time
.- Parameters:
base_time – base time for determining a presentaton time
- get_timings(frame_counter: int) FrameTimings | None
Retrieves a
GdkFrameTimings
object holding timing information for the current frame or a recent frame.The
GdkFrameTimings
object may not yet be complete: seeget_complete
andget_history_start
.- Parameters:
frame_counter – the frame counter value identifying the frame to be received
- request_phase(phase: FrameClockPhase) None
Asks the frame clock to run a particular phase.
The signal corresponding the requested phase will be emitted the next time the frame clock processes. Multiple calls to
request_phase()
will be combined together and only one frame processed. If you are displaying animated content and want to continually request theUPDATE
phase for a period of time, you should usebegin_updating
instead, since this allows GTK to adjust system parameters to get maximally smooth animations.- Parameters:
phase – the phase that is requested
Signals
- class FrameClock.signals
- after_paint() None
This signal ends processing of the frame.
Applications should generally not handle this signal.
- before_paint() None
Begins processing of the frame.
Applications should generally not handle this signal.
- flush_events() None
Used to flush pending motion events that are being batched up and compressed together.
Applications should not handle this signal.
- layout() None
Emitted as the second step of toolkit and application processing of the frame.
Any work to update sizes and positions of application elements should be performed. GTK normally handles this internally.
- paint() None
Emitted as the third step of toolkit and application processing of the frame.
The frame is repainted. GDK normally handles this internally and emits
render
signals which are turned into GtkWidget::snapshot signals by GTK.
- resume_events() None
Emitted after processing of the frame is finished.
This signal is handled internally by GTK to resume normal event processing. Applications should not handle this signal.
- update() None
Emitted as the first step of toolkit and application processing of the frame.
Animations should be updated using
get_frame_time
. Applications can connect directly to this signal, or use gtk_widget_add_tick_callback() as a more convenient interface.