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pwg: add section about query function

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This commit is contained in:
Wim Taymans 2012-10-16 11:20:59 +02:00
parent 3f3473772f
commit 626fcb3707
3 changed files with 82 additions and 2 deletions
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10
docs/pwg/building-boiler.xml
View file

@ -378,6 +378,7 @@ gst_my_filter_init (GstMyFilter * filter)
correct template would look like this:
</para>
<programlisting>
<![CDATA[
static GstStaticPadTemplate sink_factory =
GST_STATIC_PAD_TEMPLATE (
"sink",
@ -390,6 +391,7 @@ GST_STATIC_PAD_TEMPLATE (
"rate = (int) [ 8000, 96000 ]"
)
);
]]>
</programlisting>
<para>
Values surrounded by curly brackets (<quote>{</quote> and
@ -428,7 +430,9 @@ GST_STATIC_PAD_TEMPLATE (
Also, in this function, any supported element type in the plugin should
be registered.
</para>
<programlisting><!-- example-begin register.func -->
<programlisting>
<!-- example-begin register.func -->
<![CDATA[
static gboolean
plugin_init (GstPlugin *plugin)
{
@ -448,7 +452,9 @@ GST_PLUGIN_DEFINE (
"GStreamer",
"http://gstreamer.net/"
)
<!-- example-end register.func --></programlisting>
]]>
<!-- example-end register.func -->
</programlisting>
<para>
Note that the information returned by the plugin_init() function will be
cached in a central registry. For this reason, it is important that the

72
docs/pwg/building-queryfn.xml Normal file
View file

@ -0,0 +1,72 @@
<!-- ############ chapter ############# -->
<chapter id="chapter-building-queryfn">
<title>The query function</title>
<para>
Through the query function, your element will receive queries that it
has to reply to. These are queries like position, duration but also
about the supported formats and scheduling modes your element supports.
Queries can travel both upstream and downstream, so you can receive them
on sink pads as well as source pads.
</para>
<para>
Below follows a very simple query function that we install on the source
pad of our element.
</para>
<programlisting>
<![CDATA[
static gboolean gst_my_filter_src_query (GstPad *pad,
GstObject *parent,
GstQuery *query);
[..]
static void
gst_my_filter_init (GstMyFilter * filter)
{
[..]
/* configure event function on the pad before adding
* the pad to the element */
gst_pad_set_event_function (filter->srcpad,
gst_my_filter_src_event);
[..]
}
static gboolean
gst_my_filter_src_query (GstPad *pad,
GstObject *parent,
GstQuery *query)
{
gboolean ret;
GstMyFilter *filter = GST_MY_FILTER (parent);
switch (GST_QUERY_TYPE (query)) {
case GST_QUERY_POSITION:
/* we should report the current position */
[...]
break;
case GST_QUERY_DURATION:
/* we should report the duration here */
[...]
break;
case GST_QUERY_CAPS:
/* we should report the supported caps here */
[...]
break;
default:
/* just call the default handler */
ret = gst_pad_query_default (pad, parent, query);
break;
}
return ret;
}
]]>
</programlisting>
<para>
It is a good idea to call the default query handler
<function>gst_pad_query_default ()</function> for unknown queries.
Depending on the query type, the default handler will forward
the query or simply unref it.
</para>
</chapter>

2
docs/pwg/pwg.xml
View file

@ -18,6 +18,7 @@
<!ENTITY BUILDING_PADS SYSTEM "building-pads.xml">
<!ENTITY BUILDING_CHAINFN SYSTEM "building-chainfn.xml">
<!ENTITY BUILDING_EVENTFN SYSTEM "building-eventfn.xml">
<!ENTITY BUILDING_QUERYFN SYSTEM "building-queryfn.xml">
<!ENTITY BUILDING_STATE SYSTEM "building-state.xml">
<!ENTITY BUILDING_PROPS SYSTEM "building-props.xml">
<!ENTITY BUILDING_SIGNALS SYSTEM "building-signals.xml">
@ -120,6 +121,7 @@
&BUILDING_PADS;
&BUILDING_CHAINFN;
&BUILDING_EVENTFN;
&BUILDING_QUERYFN;
&BUILDING_STATE;
&BUILDING_PROPS;
&BUILDING_SIGNALS;