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.

2 files changed, 15 insertions, 6 deletions

diff --git a/video/out/gl_common.c b/video/out/gl_common.c
index 638d757eea..14d7649e8b 100644
--- a/video/out/gl_common.c
+++ b/video/out/gl_common.c
@@ -243,13 +243,19 @@ static const struct gl_functions gl_functions[] = {
         .provides = MPGL_CAP_TEX_RG,
     },
     // Swap control, always an OS specific extension
+    // The OSX code loads this manually.
     {
-        .extension = "_swap_control",
+        .extension = "GLX_SGI_swap_control",
         .functions = (const struct gl_function[]) {
-            DEF_FN_NAMES(SwapInterval, "glXSwapIntervalSGI", "glXSwapInterval",
-                         "wglSwapIntervalSGI", "wglSwapInterval",
-                         "wglSwapIntervalEXT"),
-            {0}
+            DEF_FN_NAMES(SwapInterval, "glXSwapIntervalSGI"),
+            {0},
+        },
+    },
+    {
+        .extension = "WGL_EXT_swap_control",
+        .functions = (const struct gl_function[]) {
+            DEF_FN_NAMES(SwapInterval, "wglSwapIntervalEXT"),
+            {0},
         },
     },
     {
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)