vo_opengl: cleanup swap_control extension loading

Instead of somehow looking for the substring "_swap_control" and trying
to several arbitrary function names, do it cleanly. The old approach has
the problem that it's not very exact, and may even load a pointer to a
function which doesn't exist. (Some GL implementations like Mesa return
function pointers even the functions which don't exist, and calling them
crashes.)

I couldn't find any evidence that glXSwapInterval, wglSwapIntervalSGI,
or wglSwapInterval actually exist, so don't include them. They were
carried over from MPlayer times.

To make diagnostics easier, print a warning in verbose mode if the
function could not be loaded.

1 files changed, 4 insertions, 1 deletions

diff --git a/video/out/vo_opengl.c b/video/out/vo_opengl.c
index 25e25a2e9d..9cf58286e2 100644
--- a/video/out/vo_opengl.c
+++ b/video/out/vo_opengl.c
@@ -463,8 +463,11 @@ static int preinit(struct vo *vo)
 
     mpgl_lock(p->glctx);
 
-    if (p->gl->SwapInterval)
+    if (p->gl->SwapInterval) {
         p->gl->SwapInterval(p->swap_interval);
+    } else {
+        MP_VERBOSE(vo, "swap_control extension missing.\n");
+    }
 
     p->renderer = gl_video_init(p->gl, vo->log);
     if (!p->renderer)