vo_opengl: add check-pattern suboption for testing

This uses glXGetVideoSyncSGI() to check how many vsyncs happened since
the last flip_page() call. It allows checking a pattern of vsync
increments of at most 2 elements. For example, to check ~24 fps playback
on a ~60 Hz monitor, this can be used:

--vo=opengl:check-pattern=[3-2]:waitvsync

Whether the reported results are accurate or just plain wrong may depend
on the driver and if the waitvsync sub-option is used. There are no
guarantees.

This option is undocumented, and may be removed again in the near or
distant future.

1 files changed, 28 insertions, 2 deletions

diff --git a/video/out/vo_opengl.c b/video/out/vo_opengl.c
index fdf70ac2dd..a3be9bb1e7 100644
--- a/video/out/vo_opengl.c
+++ b/video/out/vo_opengl.c
@@ -76,6 +76,11 @@ struct gl_priv {
 
     int frames_rendered;
     unsigned int prev_sgi_sync_count;
+
+    // check-pattern sub-option; for testing/debugging
+    int opt_pattern[2];
+    int last_pattern;
+    int matches, mismatches;
 };
 
 // Always called under mpgl_lock
@@ -95,6 +100,22 @@ static void resize(struct gl_priv *p)
     vo->want_redraw = true;
 }
 
+static void check_pattern(struct vo *vo, int item)
+{
+    struct gl_priv *p = vo->priv;
+    int expected = p->opt_pattern[p->last_pattern];
+    if (item == expected) {
+        p->last_pattern++;
+        if (p->last_pattern >= 2)
+            p->last_pattern = 0;
+        p->matches++;
+    } else {
+        p->mismatches++;
+        MP_WARN(vo, "wrong pattern, exptected %d got %d (hit: %d, mis: %d)\n",
+                expected, item, p->matches, p->mismatches);
+    }
+}
+
 static void flip_page(struct vo *vo)
 {
     struct gl_priv *p = vo->priv;
@@ -111,17 +132,21 @@ static void flip_page(struct vo *vo)
     if (p->use_glFinish)
         gl->Finish();
 
-    if (p->waitvsync) {
+    if (p->waitvsync || p->opt_pattern[0]) {
         if (gl->GetVideoSync) {
             unsigned int n1 = 0, n2 = 0;
             gl->GetVideoSync(&n1);
-            gl->WaitVideoSync(2, (n1 + 1) % 2, &n2);
+            if (p->waitvsync)
+                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);
+            if (p->opt_pattern[0])
+                check_pattern(vo, step);
         } else {
             MP_WARN(vo, "GLX_SGI_video_sync not available, disabling.\n");
             p->waitvsync = 0;
+            p->opt_pattern[0] = 0;
         }
     }
 
@@ -476,6 +501,7 @@ const struct m_option options[] = {
     OPT_FLAG("debug", use_gl_debug, 0),
     OPT_STRING_VALIDATE("backend", backend, 0, mpgl_validate_backend_opt),
     OPT_FLAG("sw", allow_sw, 0),
+    OPT_INTPAIR("check-pattern", opt_pattern, 0),
 
     OPT_SUBSTRUCT("", renderer_opts, gl_video_conf, 0),
     OPT_SUBSTRUCT("", icc_opts, mp_icc_conf, 0),