Gdk.FrameClock¶

class — extends GObject.Object

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 FrameClock.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. FrameClockPhase.UPDATE and the FrameClock.update signal are most interesting for application writers, and are used to update the animations, using the frame time given by FrameClock.get_frame_time.

The frame time is reported in microseconds and generally in the same timescale as GLib.get_monotonic_time, however, it is not the same as GLib.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 FrameClock.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 FrameClock.get_frame_time and the value inside the FrameClock.update signal of the clock, they will stay exactly synchronized.

Methods¶

begin_updating¶

def begin_updating(self) -> None

Starts updates for an animation.

Until a matching call to FrameClock.end_updating is made, the frame clock will continually request a new frame with the FrameClockPhase.UPDATE phase. This function may be called multiple times and frames will be requested until FrameClock.end_updating is called the same number of times.

end_updating¶

def end_updating(self) -> None

Stops updates for an animation.

See the documentation for FrameClock.begin_updating.

get_current_timings¶

def get_current_timings(self) -> FrameTimings | None

Gets the frame timings for the current frame.

get_fps¶

def get_fps(self) -> float

Calculates the current frames-per-second, based on the frame timings of frame_clock.

get_frame_counter¶

def get_frame_counter(self) -> int

GdkFrameClock maintains a 64-bit counter that increments for each frame drawn.

get_frame_time¶

def get_frame_time(self) -> 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¶

def get_history_start(self) -> int

Returns the frame counter for the oldest frame available in history.

GdkFrameClock internally keeps a history of GdkFrameTimings objects for recent frames that can be retrieved with FrameClock.get_timings. The set of stored frames is the set from the counter values given by FrameClock.get_history_start and FrameClock.get_frame_counter, inclusive.

get_refresh_info¶

def get_refresh_info(self, 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¶

def get_timings(self, 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: see FrameTimings.get_complete and FrameClock.get_history_start.

Parameters:

frame_counter — the frame counter value identifying the frame to be received

request_phase¶

def request_phase(self, phase: FrameClockPhase | int) -> 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 FrameClock.request_phase will be combined together and only one frame processed. If you are displaying animated content and want to continually request the FrameClockPhase.UPDATE phase for a period of time, you should use FrameClock.begin_updating instead, since this allows GTK to adjust system parameters to get maximally smooth animations.

Parameters:

phase — the phase that is requested

Signals¶

after-paint¶

def on_after_paint(self) -> None: ...

This signal ends processing of the frame.

Applications should generally not handle this signal.

before-paint¶

def on_before_paint(self) -> None: ...

Begins processing of the frame.

Applications should generally not handle this signal.

flush-events¶

def on_flush_events(self) -> None: ...

Used to flush pending motion events that are being batched up and compressed together.

Applications should not handle this signal.

layout¶

def on_layout(self) -> 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¶

def on_paint(self) -> 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 Surface.render signals which are turned into GtkWidget::snapshot signals by GTK.

resume-events¶

def on_resume_events(self) -> 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¶

def on_update(self) -> None: ...

Emitted as the first step of toolkit and application processing of the frame.

Animations should be updated using FrameClock.get_frame_time. Applications can connect directly to this signal, or use Gtk.Widget.add_tick_callback as a more convenient interface.