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Add meta_compositor_monotonic_time_to_server_time()

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Add a function to convert from g_get_monotonic_time() to a
"high-resolution server timestamp" with microsecond precision.
These timestamps will be used when communicating frame timing
information to the client.

https://bugzilla.gnome.org/show_bug.cgi?id=685463
This commit is contained in:
Owen W. Taylor 2012-11-12 14:09:38 -05:00
parent 0d36f4f1dd
commit 4b332640eb
2 changed files with 55 additions and 0 deletions
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7
src/compositor/compositor-private.h
View File

@ -25,6 +25,10 @@ struct _MetaCompositor
MetaPlugin *modal_plugin;
gint64 server_time_query_time;
gint64 server_time_offset;
guint server_time_is_monotonic_time : 1;
guint show_redraw : 1;
guint debug : 1;
guint no_mipmaps : 1;
@ -65,6 +69,9 @@ void meta_end_modal_for_plugin (MetaScreen *screen,
MetaPlugin *plugin,
guint32 timestamp);
gint64 meta_compositor_monotonic_time_to_server_time (MetaDisplay *display,
gint64 monotonic_time);
void meta_check_end_modal (MetaScreen *screen);
#endif /* META_COMPOSITOR_PRIVATE_H */

48
src/compositor/compositor.c
View File

@ -1414,3 +1414,51 @@ meta_compositor_flash_screen (MetaCompositor *compositor,
"signal-after::completed", flash_in_completed, flash,
NULL);
}
/**
* meta_compositor_monotonic_time_to_server_time:
* @display: a #MetaDisplay
* @monotonic_time: time in the units of g_get_monotonic_time()
*
* _NET_WM_FRAME_DRAWN and _NET_WM_FRAME_TIMINGS messages represent time
* as a "high resolution server time" - this is the server time interpolated
* to microsecond resolution. The advantage of this time representation
* is that if X server is running on the same computer as a client, and
* the Xserver uses 'clock_gettime(CLOCK_MONOTONIC, ...)' for the server
* time, the client can detect this, and all such clients will share a
* a time representation with high accuracy. If there is not a common
* time source, then the time synchronization will be less accurate.
*/
gint64
meta_compositor_monotonic_time_to_server_time (MetaDisplay *display,
gint64 monotonic_time)
{
MetaCompositor *compositor = display->compositor;
if (compositor->server_time_query_time == 0 ||
(!compositor->server_time_is_monotonic_time &&
monotonic_time > compositor->server_time_query_time + 10000000)) /* 10 seconds */
{
guint32 server_time = meta_display_get_current_time_roundtrip (display);
gint64 server_time_usec = (gint64)server_time * 1000;
gint64 current_monotonic_time = g_get_monotonic_time ();
compositor->server_time_query_time = current_monotonic_time;
/* If the server time is within a second of the monotonic time,
* we assume that they are identical. This seems like a big margin,
* but we want to be as robust as possible even if the system
* is under load and our processing of the server response is
* delayed.
*/
if (server_time_usec > current_monotonic_time - 1000000 &&
server_time_usec < current_monotonic_time + 1000000)
compositor->server_time_is_monotonic_time = TRUE;
compositor->server_time_offset = server_time_usec - current_monotonic_time;
}
if (compositor->server_time_is_monotonic_time)
return monotonic_time;
else
return monotonic_time + compositor->server_time_offset;
}