plugins: query upstream element for a GstContext.

Fix gst_vaapi_video_context_prepare() to also query upstream elements
for a valid GstContext. Improve comments regarding the steps used to
lookup or build that context, thus conforming to the GstContext API
recommendations.

https://bugzilla.gnome.org/show_bug.cgi?id=709112

Signed-off-by: Gwenole Beauchesne <gwenole.beauchesne@intel.com>

diff --git a/gst/vaapi/gstvaapivideocontext.c b/gst/vaapi/gstvaapivideocontext.c
index 1331d4beac816f275ffad8c5e9f27dab3a4a9e9e..c33cc635d00f9bc670d1953b52731710fd8fd60f 100644 (file)
--- a/gst/vaapi/gstvaapivideocontext.c
+++ b/gst/vaapi/gstvaapivideocontext.c
@@ -98,7 +98,15 @@ run_context_query(GstElement *element, GstQuery *query)
         gst_iterator_resync(it);
     gst_iterator_free(it);
 
-    /* Ignore upstream neighbours */
+    if (g_value_get_boolean(&res))
+        return TRUE;
+
+    /* If none, ask upstream neighbour (auto-plugged case) */
+    it = gst_element_iterate_sink_pads(element);
+    while (gst_iterator_fold(it, func, &res, query) == GST_ITERATOR_RESYNC)
+        gst_iterator_resync(it);
+    gst_iterator_free(it);
+
     return g_value_get_boolean(&res);
 }
 
@@ -107,12 +115,23 @@ gst_vaapi_video_context_prepare(GstElement *element, const gchar **types)
 {
     GstContext *context;
     GstQuery *query;
+    GstMessage *msg;
 
     if (!GST_CAT_CONTEXT)
         GST_DEBUG_CATEGORY_GET(GST_CAT_CONTEXT, "GST_CONTEXT");
 
-    /* (2) Query downstream with GST_QUERY_CONTEXT for the context and
-       check if downstream already has a context of the specified type */
+    /*  1) Check if the element already has a context of the specific
+     *     type, i.e. it was previously set via
+     *     gst_element_set_context(). */
+    /* This was already done by the caller of this function:
+     * gst_vaapi_ensure_display() */
+
+    /* 2) Query downstream with GST_QUERY_CONTEXT for the context and
+          check if downstream already has a context of the specific
+          type */
+    /* 3) Query upstream with GST_QUERY_CONTEXT for the context and
+          check if upstream already has a context of the specific
+          type */
     context = NULL;
     query = gst_query_new_context(GST_VAAPI_DISPLAY_CONTEXT_TYPE_NAME);
     if (run_context_query(element, query)) {
@@ -122,24 +141,26 @@ gst_vaapi_video_context_prepare(GstElement *element, const gchar **types)
         gst_element_set_context(element, context);
     }
     else {
-        /* (3) Post a GST_MESSAGE_NEED_CONTEXT message on the bus with
-           the required context types and afterwards check if a usable
-           context was set now as in (1). The message could be handled
-           by the parent bins of the element and the application */
-        GstMessage *msg;
-
+        /* 4) Post a GST_MESSAGE_NEED_CONTEXT message on the bus with
+              the required context types and afterwards check if an
+              usable context was set now as in 1). The message could
+              be handled by the parent bins of the element and the
+              application. */
         GST_CAT_INFO_OBJECT(GST_CAT_CONTEXT, element,
             "posting `need-context' message");
         msg = gst_message_new_need_context(GST_OBJECT_CAST(element),
             GST_VAAPI_DISPLAY_CONTEXT_TYPE_NAME);
         gst_element_post_message(element, msg);
+
+        /* The check of an usable context is done by the caller:
+           gst_vaapi_ensure_display() */
     }
+
     gst_query_unref(query);
 }
 
-/* (4) Create context by itself and post a GST_MESSAGE_HAVE_CONTEXT
-   message and send a GST_EVENT_CONTEXT event downstream, thus
-   containing the complete context information at this time */
+/* 5) Create a context by itself and post a GST_MESSAGE_HAVE_CONTEXT message
+      on the bus. */
 void
 gst_vaapi_video_context_propagate(GstElement *element, GstVaapiDisplay *display)
 {