Frame clock
Frame clock — Frame clock syncs painting to a window or display
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Object Hierarchy
GObject
╰── GdkFrameClock
Includes
#include <gdk/gdkwayland.h>
Description
A GdkFrameClock tells the application when to update and repaint a
window. 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
gdk_frame_clock_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. GDK_FRAME_CLOCK_PHASE_UPDATE and the
“update” signal are most interesting for application
writers, and are used to update the animations, using the frame time
given by gdk_frame_clock_get_frame_time().
The frame time is reported in microseconds and generally in the same
timescale as g_get_monotonic_time(), however, it is not the same
as g_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 gdk_frame_clock_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 gdk_frame_clock_get_frame_time()
and the value inside the “update” signal of the clock,
they will stay exactly synchronized.
Functions
gdk_frame_clock_get_frame_time ()
gint64
gdk_frame_clock_get_frame_time (GdkFrameClock *frame_clock);
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.
Since: 3.8
gdk_frame_clock_request_phase ()
void
gdk_frame_clock_request_phase (GdkFrameClock *frame_clock,
GdkFrameClockPhase phase);
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
gdk_frame_clock_request_phase() will be combined together
and only one frame processed. If you are displaying animated
content and want to continually request the
GDK_FRAME_CLOCK_PHASE_UPDATE phase for a period of time,
you should use gdk_frame_clock_begin_updating() instead, since
this allows GTK+ to adjust system parameters to get maximally
smooth animations.
Since: 3.8
gdk_frame_clock_get_frame_counter ()
gint64
gdk_frame_clock_get_frame_counter (GdkFrameClock *frame_clock);
A GdkFrameClock maintains a 64-bit counter that increments for
each frame drawn.
Returns
inside frame processing, the value of the frame counter
for the current frame. Outside of frame processing, the frame
counter for the last frame.
Since: 3.8
gdk_frame_clock_get_current_timings ()
GdkFrameTimings *
gdk_frame_clock_get_current_timings (GdkFrameClock *frame_clock);
Gets the frame timings for the current frame.
Returns
the GdkFrameTimings for the
frame currently being processed, or even no frame is being
processed, for the previous frame. Before any frames have been
processed, returns NULL.
[nullable][transfer none]
Since: 3.8
gdk_frame_clock_get_refresh_info ()
void
gdk_frame_clock_get_refresh_info (GdkFrameClock *frame_clock,
gint64 base_time,
gint64 *refresh_interval_return,
gint64 *presentation_time_return);
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
.
Since: 3.8
Types and Values
GdkFrameClock
typedef struct _GdkFrameClock GdkFrameClock;
enum GdkFrameClockPhase
GdkFrameClockPhase is used to represent the different paint clock
phases that can be requested. The elements of the enumeration
correspond to the signals of GdkFrameClock.
Since: 3.8
Signal Details
The “after-paint” signal
void
user_function (GdkFrameClock *clock,
gpointer user_data)
This signal ends processing of the frame. Applications
should generally not handle this signal.
Flags: Run Last
The “before-paint” signal
void
user_function (GdkFrameClock *clock,
gpointer user_data)
This signal begins processing of the frame. Applications
should generally not handle this signal.
Flags: Run Last
The “flush-events” signal
void
user_function (GdkFrameClock *clock,
gpointer user_data)
This signal is used to flush pending motion events that
are being batched up and compressed together. Applications
should not handle this signal.
Flags: Run Last
The “layout” signal
void
user_function (GdkFrameClock *clock,
gpointer user_data)
This signal is 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.
Flags: Run Last
The “paint” signal
void
user_function (GdkFrameClock *clock,
gpointer user_data)
This signal is emitted as the third step of toolkit and
application processing of the frame. The frame is
repainted. GDK normally handles this internally and
produces expose events, which are turned into GTK+
“draw” signals.
Flags: Run Last
The “resume-events” signal
void
user_function (GdkFrameClock *clock,
gpointer user_data)
This signal is emitted after processing of the frame is
finished, and is handled internally by GTK+ to resume normal
event processing. Applications should not handle this signal.
Flags: Run Last
The “update” signal
void
user_function (GdkFrameClock *clock,
gpointer user_data)
This signal is emitted as the first step of toolkit and
application processing of the frame. Animations should
be updated using gdk_frame_clock_get_frame_time().
Applications can connect directly to this signal, or
use gtk_widget_add_tick_callback() as a more convenient
interface.
Flags: Run Last