FrameClock

class FrameClock(**properties: Any)

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 the UPDATE phase. This function may be called multiple times and frames will be requested until end_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 of GdkFrameTimings objects for recent frames that can be retrieved with get_timings. The set of stored frames is the set from the counter values given by get_history_start and get_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: see get_complete and get_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 the UPDATE phase for a period of time, you should use begin_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.