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#include <time.h>
#include "osdep/timer.h"
#include "oml_sync.h"
#include "video/out/vo.h"
// General nonsense about the associated extension.
//
// This extension returns two unrelated values:
// (ust, msc): clock time and incrementing counter of last vsync (this is
// reported continuously, even if we don't swap)
// sbc: swap counter of frame that was last displayed (every swap
// increments the user_sbc, and the reported sbc is the sbc
// of the frame that was just displayed)
// Invariants:
// - ust and msc change in lockstep (no value can change without the other)
// - msc is incremented; if you query it in a loop, and your thread isn't
// frozen or starved by the scheduler, it will usually either not change, or
// be incremented by 1 (while the ust will be incremented by vsync
// duration)
// - sbc is never higher than the user_sbc
// - (ust, msc) are equal to or higher by vsync increments than the display
// time of the frame referenced by the sbc
// Note that (ust, msc) and sbc are not locked to each other. The following
// can easily happen if vsync skips occur:
// - you draw a frame, in the meantime hardware swaps sbc_1
// - another display vsync happens during drawing
// - you call swap()
// - query (ust, msc) and sbc
// - sbc contains sbc_1, but (ust, msc) contains the vsync after it
// As a consequence, it's hard to detect the latency or vsync skips.
static void oml_sync_reset(struct oml_sync *oml)
{
oml->vsync_duration = -1;
oml->last_skipped_vsyncs = -1;
oml->last_queue_display_time = -1;
}
void oml_sync_swap(struct oml_sync *oml, int64_t ust, int64_t msc, int64_t sbc)
{
if (!oml->state_ok)
oml_sync_reset(oml);
oml->last_skipped_vsyncs = 0;
oml->user_sbc += 1;
if (sbc < 0)
return;
oml->state_ok = true;
int64_t ust_passed = oml->last_ust ? ust - oml->last_ust : 0;
oml->last_ust = ust;
int64_t msc_passed = oml->last_msc ? msc - oml->last_msc : 0;
oml->last_msc = msc;
int64_t sbc_passed = sbc - oml->last_sbc;
oml->last_sbc = sbc;
// Display frame duration. This makes assumptions about UST (see below).
if (msc_passed && ust_passed)
oml->vsync_duration = ust_passed / msc_passed;
// Only if a new frame was displayed (sbc increased) we have sort-of a
// chance that the current (ust, msc) is for the sbc. But this is racy,
// because skipped frames drops could have increased the msc right after the
// display event and before we queried the values. This code hopes for the
// best and ignores this.
if (sbc_passed) {
// The GLX extension spec doesn't define what the UST is (not even its
// unit). Simply assume UST is a simple CLOCK_MONOTONIC usec value. This
// is what Mesa does, and what the Google EGL extension seems to imply
// (they mention CLOCK_MONOTONIC, but not the unit).
// The swap buffer call happened "some" but very small time ago, so we
// can get away with querying the current time. There is also the
// implicit assumption that mpv's timer and the UST use the same clock
// (which it does on POSIX).
struct timespec ts;
if (clock_gettime(CLOCK_MONOTONIC, &ts))
return;
uint64_t now_monotonic = ts.tv_sec * 1000000LL + ts.tv_nsec / 1000;
uint64_t ust_mp_time = mp_time_us() - (now_monotonic - ust);
// Assume this is exactly when the actual display event for this sbc
// happened. This is subject to the race mentioned above.
oml->last_sbc_mp_time = ust_mp_time;
}
// At least one frame needs to be actually displayed before
// oml->last_sbc_mp_time is set.
if (!sbc)
return;
// Extrapolate from the last sbc time (when a frame was actually displayed),
// and by adding the number of frames that were queued since to it.
// For every unit the sbc is smaller than user_sbc, the actual display
// is one frame ahead (assumes oml_sync_swap() is called for every
// vsync).
oml->last_queue_display_time =
oml->last_sbc_mp_time + (oml->user_sbc - sbc) * oml->vsync_duration;
}
void oml_sync_get_info(struct oml_sync *oml, struct vo_vsync_info *info)
{
if (!oml->state_ok)
oml_sync_reset(oml);
info->vsync_duration = oml->vsync_duration;
info->skipped_vsyncs = oml->last_skipped_vsyncs;
info->last_queue_display_time = oml->last_queue_display_time;
}
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