plugins: add gst_vaapi_plugin_base_find_gl_context()

Using the GstContext mechanism, it is possible to find if the pipeline
shares a GstGLContext, even if we are not to negotiating GLTextureUpload
meta. This is interesting because we could negotiate system memory caps
feature, but enable DMABuf if the GstGLContext is EGL with some extensions.

https://bugzilla.gnome.org/show_bug.cgi?id=766206

gst/vaapi/gstvaapipluginbase.c

@@ -206,6 +206,17 @@ error_create_proxy:
   }
 }
 
+static void
+gst_vaapi_plugin_base_find_gl_context (GstVaapiPluginBase * plugin)
+{
+  GstObject *gl_context;
+
+  if (!gst_vaapi_find_gl_local_context (GST_ELEMENT_CAST (plugin), &gl_context))
+    return;
+  gst_vaapi_plugin_base_set_gl_context (plugin, gl_context);
+  gst_object_unref (gl_context);
+}
+
 void
 gst_vaapi_plugin_base_class_init (GstVaapiPluginBaseClass * klass)
 {
@@ -363,6 +374,10 @@ gst_vaapi_plugin_base_ensure_display (GstVaapiPluginBase * plugin)
     return TRUE;
   gst_vaapi_display_replace (&plugin->display, NULL);
 
+  /* Query for a local GstGL context. If it's found, it will be used
+   * to create the VA display */
+  gst_vaapi_plugin_base_find_gl_context (plugin);
+
   if (!gst_vaapi_ensure_display (GST_ELEMENT (plugin),
           plugin->display_type_req))
     return FALSE;
@@ -750,10 +765,6 @@ gst_vaapi_plugin_base_decide_allocation (GstVaapiPluginBase * plugin,
   if (!caps)
     goto error_no_caps;
 
-  /* We don't need any GL context beyond this point if not requested
-     so explicitly through GstVideoGLTextureUploadMeta */
-  gst_object_replace (&plugin->gl_context, NULL);
-
   pool_options = 0;
   if (gst_query_find_allocation_meta (query, GST_VIDEO_META_API_TYPE, NULL))
     pool_options |= GST_VAAPI_VIDEO_BUFFER_POOL_OPTION_VIDEO_META;
@@ -766,7 +777,8 @@ gst_vaapi_plugin_base_decide_allocation (GstVaapiPluginBase * plugin,
     pool_options |= GST_VAAPI_VIDEO_BUFFER_POOL_OPTION_GL_TEXTURE_UPLOAD;
 
 #if USE_GST_GL_HELPERS
-  if (pool_options & GST_VAAPI_VIDEO_BUFFER_POOL_OPTION_GL_TEXTURE_UPLOAD) {
+  if (!plugin->gl_context &&
+      (pool_options & GST_VAAPI_VIDEO_BUFFER_POOL_OPTION_GL_TEXTURE_UPLOAD)) {
     const GstStructure *params;
     GstObject *gl_context;
 
@@ -1007,6 +1019,9 @@ gst_vaapi_plugin_base_set_gl_context (GstVaapiPluginBase * plugin,
   GstGLContext *const gl_context = GST_GL_CONTEXT (object);
   GstVaapiDisplayType display_type;
 
+  if (plugin->gl_context == object)
+    return;
+
   gst_object_replace (&plugin->gl_context, object);
 
   switch (gst_gl_context_get_gl_platform (gl_context)) {
@@ -1024,6 +1039,7 @@ gst_vaapi_plugin_base_set_gl_context (GstVaapiPluginBase * plugin,
       display_type = plugin->display_type;
       break;
   }
+  GST_INFO_OBJECT (plugin, "GL context: %" GST_PTR_FORMAT, plugin->gl_context);
   gst_vaapi_plugin_base_set_display_type (plugin, display_type);
 #endif
 }

gst/vaapi/gstvaapivideocontext.c

@@ -25,6 +25,9 @@
 
 #include "gstcompat.h"
 #include "gstvaapivideocontext.h"
+#if USE_GST_GL_HELPERS
+# include <gst/gl/gl.h>
+#endif
 
 GST_DEBUG_CATEGORY_STATIC (GST_CAT_CONTEXT);
 
@@ -233,3 +236,40 @@ gst_vaapi_video_context_propagate (GstElement * element,
   msg = gst_message_new_have_context (GST_OBJECT_CAST (element), context);
   gst_element_post_message (GST_ELEMENT_CAST (element), msg);
 }
+
+gboolean
+gst_vaapi_find_gl_local_context (GstElement * element,
+    GstObject ** gl_context_ptr)
+{
+#if USE_GST_GL_HELPERS
+  GstQuery *query;
+  GstContext *context;
+  const GstStructure *s;
+  GstObject *gl_context;
+
+  g_return_val_if_fail (gl_context_ptr, FALSE);
+
+  gl_context = NULL;
+  query = gst_query_new_context ("gst.gl.local_context");
+  if (_gst_context_run_query (element, query, GST_PAD_SRC)) {
+    gst_query_parse_context (query, &context);
+    if (context) {
+      s = gst_context_get_structure (context);
+      gst_structure_get (s, "context", GST_GL_TYPE_CONTEXT, &gl_context, NULL);
+    }
+  }
+  if (!gl_context && _gst_context_run_query (element, query, GST_PAD_SINK)) {
+    gst_query_parse_context (query, &context);
+    if (context) {
+      s = gst_context_get_structure (context);
+      gst_structure_get (s, "context", GST_GL_TYPE_CONTEXT, &gl_context, NULL);
+    }
+  }
+  gst_query_unref (query);
+  if (gl_context) {
+    *gl_context_ptr = gl_context;
+    return TRUE;
+  }
+#endif
+  return FALSE;
+}

gst/vaapi/gstvaapivideocontext.h

@@ -56,4 +56,9 @@ void
 gst_vaapi_video_context_propagate (GstElement * element,
     GstVaapiDisplay * display);
 
+G_GNUC_INTERNAL
+gboolean
+gst_vaapi_find_gl_local_context (GstElement * element,
+    GstObject ** gl_context_ptr);
+
 #endif /* GST_VAAPI_VIDEO_CONTEXT_H */