Frame clock

## Frame clock Frame clock — Frame clock syncs painting to a window or display |

## Synopsis

    #include <gdk/gdk.h>

                        GdkFrameClock;
    gint64              gdk_frame_clock_get_frame_time      (GdkFrameClock *frame_clock);
    enum                GdkFrameClockPhase;
    void                gdk_frame_clock_request_phase       (GdkFrameClock *frame_clock,
                                                             GdkFrameClockPhase phase);
    void                gdk_frame_clock_begin_updating      (GdkFrameClock *frame_clock);
    void                gdk_frame_clock_end_updating        (GdkFrameClock *frame_clock);
    gint64              gdk_frame_clock_get_frame_counter   (GdkFrameClock *frame_clock);
    gint64              gdk_frame_clock_get_history_start   (GdkFrameClock *frame_clock);
    GdkFrameTimings *   gdk_frame_clock_get_timings         (GdkFrameClock *frame_clock,
                                                             gint64 frame_counter);
    GdkFrameTimings *   gdk_frame_clock_get_current_timings (GdkFrameClock *frame_clock);
    void                gdk_frame_clock_get_refresh_info    (GdkFrameClock *frame_clock,
                                                             gint64 base_time,
                                                             gint64 *refresh_interval_return,
                                                             gint64 *presentation_time_return);

## 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.

## Details

### GdkFrameClock

    typedef struct {
      GObject parent_instance;
    } GdkFrameClock;

### 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.

`frame_clock` : | a GdkFrameClock
Returns : | a timestamp in microseconds, in the timescale of of `g_get_monotonic_time()`.

Since 3.8

### enum GdkFrameClockPhase

    typedef enum {
      GDK_FRAME_CLOCK_PHASE_NONE          = 0,
      GDK_FRAME_CLOCK_PHASE_FLUSH_EVENTS  = 1 << 0,
      GDK_FRAME_CLOCK_PHASE_BEFORE_PAINT  = 1 << 1,
      GDK_FRAME_CLOCK_PHASE_UPDATE        = 1 << 2,
      GDK_FRAME_CLOCK_PHASE_LAYOUT        = 1 << 3,
      GDK_FRAME_CLOCK_PHASE_PAINT         = 1 << 4,
      GDK_FRAME_CLOCK_PHASE_RESUME_EVENTS = 1 << 5,
      GDK_FRAME_CLOCK_PHASE_AFTER_PAINT   = 1 << 6
    } 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 GdkPaintClock.

`GDK_FRAME_CLOCK_PHASE_NONE` | no phase
`GDK_FRAME_CLOCK_PHASE_FLUSH_EVENTS` | corresponds to GdkFrameClock::flush-events. Should not be handled by applications.
`GDK_FRAME_CLOCK_PHASE_BEFORE_PAINT` | corresponds to GdkFrameClock::before-paint. Should not be handled by applications.
`GDK_FRAME_CLOCK_PHASE_UPDATE` | corresponds to GdkFrameClock::update.
`GDK_FRAME_CLOCK_PHASE_LAYOUT` | corresponds to GdkFrameClock::layout.
`GDK_FRAME_CLOCK_PHASE_PAINT` | corresponds to GdkFrameClock::paint.
`GDK_FRAME_CLOCK_PHASE_RESUME_EVENTS` | corresponds to GdkFrameClock::resume-events. Should not be handled by applications.
`GDK_FRAME_CLOCK_PHASE_AFTER_PAINT` | corresponds to GdkFrameClock::after-paint. Should not be handled by applications.

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.

`frame_clock` : | a GdkFrameClock
`phase` : | the phase that is requested

Since 3.8

### gdk_frame_clock_begin_updating ()

    void                gdk_frame_clock_begin_updating      (GdkFrameClock *frame_clock);

Starts updates for an animation. Until a matching call to `gdk_frame_clock_end_updating()` is made, the frame clock will continually request a new frame with the `GDK_FRAME_CLOCK_PHASE_UPDATE` phase. This function may be called multiple times and frames will be requested until `gdk_frame_clock_end_updating()` is called the same number of times.

`frame_clock` : | a GdkFrameClock

Since 3.8

### gdk_frame_clock_end_updating ()

    void                gdk_frame_clock_end_updating        (GdkFrameClock *frame_clock);

Stops updates for an animation. See the documentation for `gdk_frame_clock_begin_updating()`.

`frame_clock` : | a GdkFrameClock

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.

`frame_clock` : | a GdkFrameClock
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_history_start ()

    gint64              gdk_frame_clock_get_history_start   (GdkFrameClock *frame_clock);

GdkFrameClock internally keeps a history of GdkFrameTiming objects for recent frames that can be retrieved with `gdk_frame_clock_get_timings()`. The set of stored frames is the set from the counter values given by `gdk_frame_clock_get_history_start()` and `gdk_frame_clock_get_frame_counter()`, inclusive.

`frame_clock` : | a GdkFrameClock
Returns : | the frame counter value for the oldest frame that is available in the internal frame history of the GdkFrameClock.

Since 3.8

### gdk_frame_clock_get_timings ()

    GdkFrameTimings *   gdk_frame_clock_get_timings         (GdkFrameClock *frame_clock,
                                                             gint64 frame_counter);

Retrieves a GdkFrameTimings object holding timing information for the current frame or a recent frame. The GdkFrameTimings object may not yet be complete: see `gdk_frame_timings_get_complete()`.

`frame_clock` : | a GdkFrameClock
`frame_counter` : | the frame counter value identifying the frame to be received.
Returns : | the GdkFrameTimings object for the specified frame, or `NULL` if it is not available. See `gdk_frame_clock_get_history_start()`.

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.

`frame_clock` : | a GdkFrameClock
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 procesed, returns `NULL`.

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`.

`frame_clock` : | a GdkFrameClock
`base_time` : | base time for determining a presentaton time
`refresh_interval_return` : | a location to store the determined refresh interval, or `NULL`. A default refresh interval of 1/60th of a second will be stored if no history is present.
`presentation_time_return` : | a location to store the next candidate presentation time after the given base time. 0 will be will be stored if no history is present.

Since 3.8