vo_opengl: optional support for using GLX_SGI_video_sync

I'm not sure about the merit, though it does print nice numbers if debug
output is enabled.

Basically, this tries to achieve similar results as the glFinish()
business, but again it entirely depends on the drivers whether this
does anything meaningful, or whether it's actively harmful.

1 files changed, 19 insertions, 1 deletions

diff --git a/video/out/vo_opengl.c b/video/out/vo_opengl.c
index c80506039c..fdf70ac2dd 100644
--- a/video/out/vo_opengl.c
+++ b/video/out/vo_opengl.c
@@ -66,6 +66,7 @@ struct gl_priv {
     struct gl_video_opts *renderer_opts;
     struct mp_icc_opts *icc_opts;
     int use_glFinish;
+    int waitvsync;
     int use_gl_debug;
     int allow_sw;
     int swap_interval;
@@ -74,6 +75,7 @@ struct gl_priv {
     int vo_flipped;
 
     int frames_rendered;
+    unsigned int prev_sgi_sync_count;
 };
 
 // Always called under mpgl_lock
@@ -96,6 +98,7 @@ static void resize(struct gl_priv *p)
 static void flip_page(struct vo *vo)
 {
     struct gl_priv *p = vo->priv;
+    GL *gl = p->gl;
 
     mpgl_lock(p->glctx);
 
@@ -106,7 +109,21 @@ static void flip_page(struct vo *vo)
         gl_video_set_debug(p->renderer, false);
 
     if (p->use_glFinish)
-        p->gl->Finish();
+        gl->Finish();
+
+    if (p->waitvsync) {
+        if (gl->GetVideoSync) {
+            unsigned int n1 = 0, n2 = 0;
+            gl->GetVideoSync(&n1);
+            gl->WaitVideoSync(2, (n1 + 1) % 2, &n2);
+            int step = n1 - p->prev_sgi_sync_count;
+            p->prev_sgi_sync_count = n1;
+            MP_DBG(vo, "Flip counts: %u->%u, step=%d\n", n1, n2, step);
+        } else {
+            MP_WARN(vo, "GLX_SGI_video_sync not available, disabling.\n");
+            p->waitvsync = 0;
+        }
+    }
 
     mpgl_unlock(p->glctx);
 }
@@ -454,6 +471,7 @@ err_out:
 #define OPT_BASE_STRUCT struct gl_priv
 const struct m_option options[] = {
     OPT_FLAG("glfinish", use_glFinish, 0),
+    OPT_FLAG("waitvsync", waitvsync, 0),
     OPT_INT("swapinterval", swap_interval, 0, OPTDEF_INT(1)),
     OPT_FLAG("debug", use_gl_debug, 0),
     OPT_STRING_VALIDATE("backend", backend, 0, mpgl_validate_backend_opt),