spa-pod: add _filter() method

lib/wp/spa-pod.c

@@ -14,6 +14,7 @@
 #include <spa/utils/type-info.h>
 #include <spa/pod/builder.h>
 #include <spa/pod/parser.h>
+#include <spa/pod/filter.h>
 
 #define WP_SPA_POD_BUILDER_REALLOC_STEP_SIZE 64
 #define WP_SPA_POD_ID_PROPERTY_NAME_MAX 16
@@ -1811,6 +1812,41 @@ wp_spa_pod_fixate (WpSpaPod *self)
   return FALSE;
 }
 
+/*!
+ * \brief Returns the intersection between \a self and \a filter
+ *
+ * This is typically used to intersect pods that describe formats, in order to
+ * find a common format that is accceptable by both sides. For that purpose,
+ * this is not exactly an intersection with its mathematical meaning.
+ * Object properties can be thought of as format constraints. When one side does
+ * not specify a specific property, it is considered to accept any value for it,
+ * so the value of this property from the other side is added in the result.
+ *
+ * Both input pods are left unmodified after this function call.
+ *
+ * If NULL is passed in the \a filter, this function just copies \a self and
+ * returns the copy.
+ *
+ * \param self the first pod
+ * \param filter (nullable): the second pod
+ * \return (transfer full) (nullable): a new pod that contains the intersection
+ *   between \a self and \a filter, or NULL if the intersection was not possible
+ *   to make
+ */
+WpSpaPod *
+wp_spa_pod_filter (WpSpaPod *self, WpSpaPod *filter)
+{
+  char buffer[1024];
+  struct spa_pod_builder b = SPA_POD_BUILDER_INIT(&buffer, sizeof(buffer));
+  struct spa_pod *result = NULL;
+
+  g_return_val_if_fail (self, NULL);
+
+  if (spa_pod_filter(&b, &result, self->pod, filter ? filter->pod : NULL) >= 0)
+    return wp_spa_pod_new_wrap_copy (result);
+  return NULL;
+}
+
 /*!
  * \brief Increases the reference count of a spa pod builder
  *

lib/wp/spa-pod.h

@@ -289,6 +289,9 @@ WpIterator *wp_spa_pod_new_iterator (WpSpaPod *pod);
 WP_API
 gboolean wp_spa_pod_fixate (WpSpaPod *self);
 
+WP_API
+WpSpaPod *wp_spa_pod_filter (WpSpaPod *self, WpSpaPod *filter);
+
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (WpSpaPod, wp_spa_pod_unref)