[gtk/wip/chergert/macos-gst-cgl] media: support OpenGL-based video playback on macOS

[Christian Hergert <chergert src gnome org>]

commit 7ec9c5181d69625b58781c1eca84d9a1a1cc20de
Author: Christian Hergert <christian hergert me>
Date:   Wed Feb 16 21:27:10 2022 -0800

    media: support OpenGL-based video playback on macOS
    
    If we have GStreamer on macOS we likely have support for CGL to get an
    OpenGL context we can use. This provides the missing pieces to get
    accelerated video playback in gtk4-widget-factory working.

 modules/media/gtkgstsink.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)
---
diff --git a/modules/media/gtkgstsink.c b/modules/media/gtkgstsink.c
index c2708da148..529952fffc 100644
--- a/modules/media/gtkgstsink.c
+++ b/modules/media/gtkgstsink.c
@@ -48,6 +48,10 @@
 #include <gst/gl/egl/gstgldisplay_egl.h>
 #endif
 
+#ifdef GDK_WINDOWING_MACOS
+#include <gdk/macos/gdkmacos.h>
+#endif
+
 #include <gst/gl/gstglfuncs.h>
 
 enum {
@@ -497,6 +501,29 @@ gtk_gst_sink_initialize_gl (GtkGstSink *self)
     }
   else
 #endif
+#if defined(GST_GL_HAVE_PLATFORM_CGL) && defined(GDK_WINDOWING_MACOS)
+  if (GDK_IS_MACOS_DISPLAY (display))
+    {
+      platform = GST_GL_PLATFORM_CGL;
+
+      GST_DEBUG_OBJECT (self, "got CGL on macOS!");
+
+      gl_api = gst_gl_context_get_current_gl_api (platform, NULL, NULL);
+      gl_handle = gst_gl_context_get_current_gl_context (platform);
+
+      if (gl_handle)
+        {
+          self->gst_display = gst_gl_display_new ();
+          self->gst_app_context = gst_gl_context_new_wrapped (self->gst_display, gl_handle, platform, 
gl_api);
+        }
+      else
+        {
+          GST_ERROR_OBJECT (self, "Failed to get handle from GdkGLContext, not using macOS CGL");
+          return FALSE;
+        }
+    }
+  else
+#endif
 #if GST_GL_HAVE_WINDOW_WIN32 && (GST_GL_HAVE_PLATFORM_WGL || GST_GL_HAVE_PLATFORM_EGL) && defined 
(GDK_WINDOWING_WIN32)
   if (GDK_IS_WIN32_DISPLAY (display))
     {