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

[Christian Hergert <chergert src gnome org>]

commit 3d19d4c0edf8b741a145e11db40fe0fb9d88b983
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..cb0fe21251 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
+#ifdef GST_GL_HAVE_PLATFORM_CGL
+  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))
     {