Package org.freedesktop.wayland.client

Interface WpPresentationFeedbackEvents

public interface WpPresentationFeedbackEvents

presentation time feedback event

A presentation_feedback object returns an indication that a wl_surface content update has become visible to the user. One object corresponds to one content update submission (wl_surface.commit). There are two possible outcomes: the content update is presented to the user, and a presentation timestamp delivered; or, the user did not see the content update because it was superseded or its surface destroyed, and the content update is discarded.

Once a presentation_feedback object has delivered a 'presented' or 'discarded' event it is automatically destroyed.

Field Summary

Fields

Modifier and Type	Field	Description
static final int	VERSION

Method Summary

Modifier and Type	Method	Description
void	discarded(WpPresentationFeedbackProxy emitter)	the content update was not displayed
void	presented(WpPresentationFeedbackProxy emitter, int tvSecHi, int tvSecLo, int tvNsec, int refresh, int seqHi, int seqLo, int flags)	the content update was displayed
void	syncOutput(WpPresentationFeedbackProxy emitter, WlOutputProxy output)	presentation synchronized to this output

Field Details

VERSION

static final int VERSION

See Also:

• Constant Field Values

Method Details

syncOutput

void syncOutput(WpPresentationFeedbackProxy emitter,
 @Nonnull
 WlOutputProxy output)

presentation synchronized to this output

As presentation can be synchronized to only one output at a time, this event tells which output it was. This event is only sent prior to the presented event.

As clients may bind to the same global wl_output multiple times, this event is sent for each bound instance that matches the synchronized output. If a client has not bound to the right wl_output global at all, this event is not sent.

Parameters:

emitter - The protocol object that emitted the event.

output - presentation output

presented

void presented(WpPresentationFeedbackProxy emitter,
 int tvSecHi,
 int tvSecLo,
 int tvNsec,
 int refresh,
 int seqHi,
 int seqLo,
 int flags)

the content update was displayed

The associated content update was displayed to the user at the indicated time (tv_sec_hi/lo, tv_nsec). For the interpretation of the timestamp, see presentation.clock_id event.

The timestamp corresponds to the time when the content update turned into light the first time on the surface's main output. Compositors may approximate this from the framebuffer flip completion events from the system, and the latency of the physical display path if known.

This event is preceded by all related sync_output events telling which output's refresh cycle the feedback corresponds to, i.e. the main output for the surface. Compositors are recommended to choose the output containing the largest part of the wl_surface, or keeping the output they previously chose. Having a stable presentation output association helps clients predict future output refreshes (vblank).

The 'refresh' argument gives the compositor's prediction of how many nanoseconds after tv_sec, tv_nsec the very next output refresh may occur. This is to further aid clients in predicting future refreshes, i.e., estimating the timestamps targeting the next few vblanks. If such prediction cannot usefully be done, the argument is zero.

If the output does not have a constant refresh rate, explicit video mode switches excluded, then the refresh argument must be zero.

The 64-bit value combined from seq_hi and seq_lo is the value of the output's vertical retrace counter when the content update was first scanned out to the display. This value must be compatible with the definition of MSC in GLX_OML_sync_control specification. Note, that if the display path has a non-zero latency, the time instant specified by this counter may differ from the timestamp's.

If the output does not have a concept of vertical retrace or a refresh cycle, or the output device is self-refreshing without a way to query the refresh count, then the arguments seq_hi and seq_lo must be zero.

Parameters:

emitter - The protocol object that emitted the event.

tvSecHi - high 32 bits of the seconds part of the presentation timestamp

tvSecLo - low 32 bits of the seconds part of the presentation timestamp

tvNsec - nanoseconds part of the presentation timestamp

refresh - nanoseconds till next refresh

seqHi - high 32 bits of refresh counter

seqLo - low 32 bits of refresh counter

flags - combination of 'kind' values

discarded

void discarded(WpPresentationFeedbackProxy emitter)

the content update was not displayed

The content update was never displayed to the user.

Parameters:

emitter - The protocol object that emitted the event.