1 files changed, 85 insertions, 0 deletions
diff --git a/video/out/present_sync.c b/video/out/present_sync.c
new file mode 100644
index 0000000000..16d7416d43
--- /dev/null
+++ b/video/out/present_sync.c
@@ -0,0 +1,85 @@
+/*
+ * This file is part of mpv.
+ *
+ * mpv is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * mpv is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with mpv.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <time.h>
+
+#include "mpv_talloc.h"
+#include "osdep/timer.h"
+#include "present_sync.h"
+
+/* General nonsense about this mechanism.
+ *
+ * This requires that that caller has access to two, related values:
+ * (ust, msc): clock time and incrementing counter of last vsync (this is
+ *             increased continuously, even if we don't swap)
+ *
+ * Note that this concept originates from the GLX_OML_sync_control extension 
+ * which includes another parameter: sbc (swap counter of frame that was
+ * last displayed). Both the xorg present extension and wayland's
+ * presentation-time protocol do not include sbc values so they are omitted
+ * from this mechanism. mpv does not need to keep track of sbc calls and can
+ * have reliable presentation without it.
+ */
+
+void present_sync_get_info(struct mp_present *present, struct vo_vsync_info *info)
+{
+    info->vsync_duration = present->vsync_duration;
+    info->skipped_vsyncs = present->last_skipped_vsyncs;
+    info->last_queue_display_time = present->last_queue_display_time;
+}
+
+void present_sync_swap(struct mp_present *present)
+{
+    int64_t ust = present->current_ust;
+    int64_t msc = present->current_msc;
+
+    // Avoid attempting to use any presentation statistics if the ust is 0 or has
+    // not actually updated (i.e. the last_ust is equal to current_ust).
+    if (!ust || ust == present->last_ust) {
+        present->last_skipped_vsyncs = -1;
+        present->vsync_duration = -1;
+        present->last_queue_display_time = -1;
+        return;
+    }
+
+    present->last_skipped_vsyncs = 0;
+
+    int64_t ust_passed = ust ? ust - present->last_ust: 0;
+    present->last_ust = ust;
+    int64_t msc_passed = msc ? msc - present->last_msc: 0;
+    present->last_msc = msc;
+
+    if (msc_passed && ust_passed)
+        present->vsync_duration = ust_passed / msc_passed;
+
+    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);
+
+    present->last_queue_display_time = ust_mp_time;
+}
+
+void present_update_sync_values(struct mp_present *present, int64_t ust,
+                                int64_t msc)
+{
+    present->current_ust = ust;
+    present->current_msc = msc;
+}