2 * Copyright (C) 2013 Collabora Ltd.
3 * Author: Sebastian Dröge <sebastian.droege@collabora.co.uk>
5 * gstcontext.h: Header for GstContext subsystem
7 * This library is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Library General Public
9 * License as published by the Free Software Foundation; either
10 * version 2 of the License, or (at your option) any later version.
12 * This library is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Library General Public License for more details.
17 * You should have received a copy of the GNU Library General Public
18 * License along with this library; if not, write to the
19 * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
20 * Boston, MA 02110-1301, USA.
25 * @short_description: Lightweight objects to represent element contexts
26 * @see_also: #GstMiniObject, #GstElement
28 * #GstContext is a container object used to store contexts like a device
29 * context, a display server connection and similar concepts that should
30 * be shared between multiple elements.
32 * Applications can set a context on a complete pipeline by using
33 * gst_element_set_context(), which will then be propagated to all
34 * child elements. Elements can handle these in GstElement::set_context()
35 * and merge them with the context information they already have.
37 * When an element needs a context it will do the following actions in this
38 * order until one step succeeds:
39 * 1) Check if the element already has a context
40 * 2) Query downstream with GST_QUERY_CONTEXT for the context
41 * 3) Post a GST_MESSAGE_NEED_CONTEXT message on the bus with the required
42 * context types and afterwards check if a usable context was set now
43 * 4) Create a context by itself and post a GST_MESSAGE_HAVE_CONTEXT message
44 * and send a GST_EVENT_CONTEXT event downstream, containing the complete
45 * context information at this time.
47 * Applications should catch the GST_MESSAGE_HAVE_CONTEXT messages and remember
48 * any content from it unless it has a custom version of a specific context. If
49 * later an element is posting a GST_MESSAGE_NEED_CONTEXT message for a specific
50 * context that was created by an element before the application should pass it
51 * to the complete pipeline.
56 #include "gst_private.h"
58 #include "gstcontext.h"
63 GstMiniObject mini_object;
65 GstStructure *structure;
68 #define GST_CONTEXT_STRUCTURE(c) (((GstContext *)(c))->structure)
70 static GType _gst_context_type = 0;
71 GST_DEFINE_MINI_OBJECT_TYPE (GstContext, gst_context);
74 _priv_gst_context_initialize (void)
76 GST_CAT_INFO (GST_CAT_GST_INIT, "init contexts");
78 /* the GstMiniObject types need to be class_ref'd once before it can be
79 * done from multiple threads;
80 * see http://bugzilla.gnome.org/show_bug.cgi?id=304551 */
81 gst_context_get_type ();
83 _gst_context_type = gst_context_get_type ();
87 _gst_context_free (GstContext * context)
89 GstStructure *structure;
91 g_return_if_fail (context != NULL);
93 GST_CAT_LOG (GST_CAT_CONTEXT, "finalize context %p: %" GST_PTR_FORMAT,
94 context, GST_CONTEXT_STRUCTURE (context));
96 structure = GST_CONTEXT_STRUCTURE (context);
98 gst_structure_set_parent_refcount (structure, NULL);
99 gst_structure_free (structure);
102 g_slice_free1 (sizeof (GstContext), context);
105 static void gst_context_init (GstContext * context);
108 _gst_context_copy (GstContext * context)
111 GstStructure *structure;
113 GST_CAT_LOG (GST_CAT_CONTEXT, "copy context %p: %" GST_PTR_FORMAT, context,
114 GST_CONTEXT_STRUCTURE (context));
116 copy = g_slice_new0 (GstContext);
118 gst_context_init (copy);
120 structure = GST_CONTEXT_STRUCTURE (context);
121 GST_CONTEXT_STRUCTURE (copy) = gst_structure_copy (structure);
122 gst_structure_set_parent_refcount (GST_CONTEXT_STRUCTURE (copy),
123 ©->mini_object.refcount);
125 return GST_CONTEXT_CAST (copy);
129 gst_context_init (GstContext * context)
131 gst_mini_object_init (GST_MINI_OBJECT_CAST (context), 0, _gst_context_type,
132 (GstMiniObjectCopyFunction) _gst_context_copy, NULL,
133 (GstMiniObjectFreeFunction) _gst_context_free);
139 * Create a new context.
141 * Returns: (transfer full): The new context.
146 gst_context_new (void)
149 GstStructure *structure;
151 context = g_slice_new0 (GstContext);
153 GST_CAT_LOG (GST_CAT_CONTEXT, "creating new context %p", context);
155 structure = gst_structure_new_id_empty (GST_QUARK (CONTEXT));
156 gst_structure_set_parent_refcount (structure, &context->mini_object.refcount);
157 gst_context_init (context);
159 GST_CONTEXT_STRUCTURE (context) = structure;
165 * gst_context_get_structure:
166 * @context: The #GstContext.
168 * Access the structure of the context.
170 * Returns: (transfer none): The structure of the context. The structure is
171 * still owned by the context, which means that you should not modify it,
172 * free it and that the pointer becomes invalid when you free the context.
177 gst_context_get_structure (GstContext * context)
179 g_return_val_if_fail (GST_IS_CONTEXT (context), NULL);
181 return GST_CONTEXT_STRUCTURE (context);
185 * gst_context_writable_structure:
186 * @context: The #GstContext.
188 * Get a writable version of the structure.
190 * Returns: The structure of the context. The structure is still
191 * owned by the event, which means that you should not free it and
192 * that the pointer becomes invalid when you free the event.
193 * This function checks if @context is writable.
198 gst_context_writable_structure (GstContext * context)
200 g_return_val_if_fail (GST_IS_CONTEXT (context), NULL);
201 g_return_val_if_fail (gst_context_is_writable (context), NULL);
203 return GST_CONTEXT_STRUCTURE (context);