GstElement: Add a more flexible way to get request pads.

The new request_new_pad_full vmethod provides an additional caps field,
which allows elements to take better decision process.

Also, add a gst_element_request_pad() function to allow developers to be
able to specify which pad template they want a pad of.

Convert gstutils to use that new method instead of the old one when more
efficient.

This is useful for being able to request pads in a more flexible way,
especially when the element can provide pads whose caps depend on
runtime configuration and therefore can't provide pre-registered
pad templates.

API: GstElement::request_new_pad_full
API: gst_element_request_pad

https://bugzilla.gnome.org/show_bug.cgi?id=637300

docs/gst/gstreamer-sections.txt

@@ -523,6 +523,7 @@ gst_element_get_compatible_pad
 gst_element_get_compatible_pad_template
 gst_element_get_request_pad
 gst_element_get_static_pad
+gst_element_request_pad
 gst_element_no_more_pads
 gst_element_release_request_pad
 gst_element_remove_pad

gst/gstelement.c

@@ -968,15 +968,17 @@ gst_element_get_static_pad (GstElement * element, const gchar * name)
 }
 
 static GstPad *
-gst_element_request_pad (GstElement * element, GstPadTemplate * templ,
-    const gchar * name)
+_gst_element_request_pad (GstElement * element, GstPadTemplate * templ,
+    const gchar * name, const GstCaps * caps)
 {
   GstPad *newpad = NULL;
   GstElementClass *oclass;
 
   oclass = GST_ELEMENT_GET_CLASS (element);
 
-  if (oclass->request_new_pad)
+  if (oclass->request_new_pad_full)
+    newpad = (oclass->request_new_pad_full) (element, templ, name, caps);
+  else if (oclass->request_new_pad)
     newpad = (oclass->request_new_pad) (element, templ, name);
 
   if (newpad)
@@ -994,6 +996,9 @@ gst_element_request_pad (GstElement * element, GstPadTemplate * templ,
  * request pads. The pad should be released with
  * gst_element_release_request_pad().
  *
+ * This method is slow and will be deprecated in the future. New code should
+ * use gst_element_request_pad() with the requested template.
+ *
  * Returns: (transfer full): requested #GstPad if found, otherwise %NULL.
  *     Release after usage.
  */
@@ -1068,11 +1073,43 @@ gst_element_get_request_pad (GstElement * element, const gchar * name)
   if (!templ_found)
     return NULL;
 
-  pad = gst_element_request_pad (element, templ, req_name);
+  pad = _gst_element_request_pad (element, templ, req_name, NULL);
 
   return pad;
 }
 
+/**
+ * gst_element_request_pad:
+ * @element: a #GstElement to find a request pad of.
+ * @templ: a #GstPadTemplate of which we want a pad of.
+ * @name: (transfer none) (allow-none): the name of the request #GstPad
+ * to retrieve. Can be %NULL.
+ * @caps: (transfer none) (allow-none): the caps of the pad we want to
+ * request. Can be %NULL.
+ *
+ * Retrieves a request pad from the element according to the provided template.
+ *
+ * If the @caps are specified and the element implements thew new
+ * request_new_pad_full virtual method, the element will use them to select
+ * which pad to create.
+ *
+ * The pad should be released with gst_element_release_request_pad().
+ *
+ * Returns: (transfer full): requested #GstPad if found, otherwise %NULL.
+ *     Release after usage.
+ *
+ * Since: 0.10.32
+ */
+GstPad *
+gst_element_request_pad (GstElement * element,
+    GstPadTemplate * templ, const gchar * name, const GstCaps * caps)
+{
+  g_return_val_if_fail (GST_IS_ELEMENT (element), NULL);
+  g_return_val_if_fail (templ != NULL, NULL);
+
+  return _gst_element_request_pad (element, templ, name, caps);
+}
+
 /**
  * gst_element_get_pad:
  * @element: a #GstElement.

gst/gstelement.h

@@ -601,6 +601,7 @@ struct _GstElement
  * @send_event: send a #GstEvent to the element
  * @get_query_types: get the supported #GstQueryType of this element
  * @query: perform a #GstQuery on the element
+ * @request_new_pad_full: called when a new pad is requested. Since: 0.10.32.
  *
  * GStreamer element class. Override the vmethods to implement the element
  * functionality.
@@ -662,7 +663,14 @@ struct _GstElementClass
   /* FIXME-0.11: move up and replace details */
   gpointer		meta_data;
 
-  gpointer _gst_reserved[GST_PADDING-1];
+  /*< public >*/
+  /* Virtual method for subclasses (additions) */
+  /* FIXME-0.11 Make this the default behaviour */
+  GstPad*		(*request_new_pad_full) (GstElement *element, GstPadTemplate *templ,
+						 const gchar* name, const GstCaps *caps);
+
+  /*< private >*/
+  gpointer _gst_reserved[GST_PADDING-2];
 };
 
 /* element class pad templates */
@@ -757,6 +765,9 @@ GstPad*                 gst_element_get_pad             (GstElement *element, co
 #endif /* GST_DISABLE_DEPRECATED */
 GstPad*                 gst_element_get_static_pad      (GstElement *element, const gchar *name);
 GstPad*                 gst_element_get_request_pad     (GstElement *element, const gchar *name);
+GstPad*                 gst_element_request_pad         (GstElement *element,
+							 GstPadTemplate *templ,
+							 const gchar * name, const GstCaps *caps);
 void                    gst_element_release_request_pad (GstElement *element, GstPad *pad);
 
 GstIterator *           gst_element_iterate_pads        (GstElement * element);

gst/gstutils.c

@@ -933,26 +933,6 @@ gst_element_get_compatible_pad_template (GstElement * element,
   return newtempl;
 }
 
-static GstPad *
-gst_element_request_pad (GstElement * element, GstPadTemplate * templ,
-    const gchar * name)
-{
-  GstPad *newpad = NULL;
-  GstElementClass *oclass;
-
-  oclass = GST_ELEMENT_GET_CLASS (element);
-
-  if (oclass->request_new_pad)
-    newpad = (oclass->request_new_pad) (element, templ, name);
-
-  if (newpad)
-    gst_object_ref (newpad);
-
-  return newpad;
-}
-
-
-
 /**
  * gst_element_get_pad_from_template:
  * @element: (transfer none): a #GstElement.
@@ -988,7 +968,7 @@ gst_element_get_pad_from_template (GstElement * element, GstPadTemplate * templ)
       break;
 
     case GST_PAD_REQUEST:
-      ret = gst_element_request_pad (element, templ, NULL);
+      ret = gst_element_request_pad (element, templ, NULL, NULL);
       break;
   }
 
@@ -1783,9 +1763,11 @@ gst_element_link_pads_full (GstElement * src, const gchar * srcpadname,
             if (gst_caps_is_always_compatible (gst_pad_template_get_caps
                     (srctempl), gst_pad_template_get_caps (desttempl))) {
               srcpad =
-                  gst_element_get_request_pad (src, srctempl->name_template);
+                  gst_element_request_pad (src, srctempl,
+                  srctempl->name_template, NULL);
               destpad =
-                  gst_element_get_request_pad (dest, desttempl->name_template);
+                  gst_element_request_pad (dest, desttempl,
+                  desttempl->name_template, NULL);
               if (srcpad && destpad
                   && pad_link_maybe_ghosting (srcpad, destpad, flags)) {
                 GST_CAT_DEBUG (GST_CAT_ELEMENT_PADS,

win32/common/libgstreamer.def

@@ -358,6 +358,7 @@ EXPORTS
 	gst_element_register
 	gst_element_release_request_pad
 	gst_element_remove_pad
+	gst_element_request_pad
 	gst_element_requires_clock
 	gst_element_seek
 	gst_element_seek_simple