1 files changed, 126 insertions, 0 deletions
diff --git a/video/out/present_sync.c b/video/out/present_sync.c
new file mode 100644
index 0000000000..a3b1089f1a
--- /dev/null
+++ b/video/out/present_sync.c
@@ -0,0 +1,126 @@
+/*
+ * 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 "misc/linked_list.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)
+{
+    struct mp_present_entry *cur = present->head;
+    while (cur) {
+        if (cur->queue_display_time)
+            break;
+        cur = cur->list_node.next;
+    }
+    if (!cur)
+        return;
+
+    info->vsync_duration = cur->vsync_duration;
+    info->skipped_vsyncs = cur->skipped_vsyncs;
+    info->last_queue_display_time = cur->queue_display_time;
+
+    // Remove from the list, zero out everything, and append at the end
+    LL_REMOVE(list_node, present, cur);
+    *cur = (struct mp_present_entry){0};
+    LL_APPEND(list_node, present, cur);
+}
+
+struct mp_present *mp_present_initialize(void *talloc_ctx, struct mp_vo_opts *opts, int entries)
+{
+    struct mp_present *present = talloc_zero(talloc_ctx, struct mp_present);
+    for (int i = 0; i < entries; i++) {
+        struct mp_present_entry *entry = talloc_zero(present, struct mp_present_entry);
+        LL_APPEND(list_node, present, entry);
+    }
+    present->opts = opts;
+    return present;
+}
+
+void present_sync_swap(struct mp_present *present)
+{
+    struct mp_present_entry *cur = present->head;
+    while (cur) {
+        if (!cur->queue_display_time)
+            break;
+        cur = cur->list_node.next;
+    }
+    if (!cur)
+        return;
+
+    int64_t ust = cur->ust;
+    int64_t msc = cur->msc;
+    int64_t last_ust = cur->list_node.prev ? cur->list_node.prev->ust : 0;
+    int64_t last_msc = cur->list_node.prev ? cur->list_node.prev->msc : 0;
+
+    // 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 ust).
+    if (!ust || ust == last_ust) {
+        cur->skipped_vsyncs = -1;
+        cur->vsync_duration = -1;
+        cur->queue_display_time = -1;
+        return;
+    }
+
+    cur->skipped_vsyncs = 0;
+    int64_t ust_passed = ust ? ust - last_ust: 0;
+    int64_t msc_passed = msc ? msc - last_msc: 0;
+    if (msc_passed && ust_passed)
+        cur->vsync_duration = ust_passed / msc_passed;
+
+    struct timespec ts;
+    if (clock_gettime(CLOCK_MONOTONIC, &ts))
+        return;
+
+    int64_t now_monotonic = MP_TIME_S_TO_NS(ts.tv_sec) + ts.tv_nsec;
+    int64_t ust_mp_time = mp_time_ns() - (now_monotonic - ust);
+    cur->queue_display_time = ust_mp_time;
+}
+
+void present_sync_update_values(struct mp_present *present, int64_t ust,
+                                int64_t msc)
+{
+    struct mp_present_entry *cur = present->head;
+    int index = 0;
+    while (cur && ++index) {
+        if (!cur->ust || index == present->opts->swapchain_depth)
+            break;
+        cur = cur->list_node.next;
+    }
+    if (!cur)
+        return;
+
+    cur->ust = ust;
+    cur->msc = msc;
+}