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246 lines
8.6 KiB
XML
246 lines
8.6 KiB
XML
<sect1 id="chapter-developing">
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<title id="title-developing">Developing applications with GStreamer</title>
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<qandaset>
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<qandaentry>
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<question id="developing-compile-programs">
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<para>How do I compile programs that use GStreamer ?</para>
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</question>
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<answer>
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<para>
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GStreamer uses pkg-config to assist applications with compilationa and
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linking flags.
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pkg-config is already used by GTK+, GNOME, SDL, and others; so if you are
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familiar with using it for any of those, you're set.
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</para>
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<para>
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If you're not familiar with pkg-config to compile and link a small
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one-file program, pass the --cflags and --libs arguments to pkg-config.
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For example:
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<programlisting>
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$ gcc `pkg-config --cflags --libs gstreamer-&GST_MAJORMINOR;` -o myprog myprog.c
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</programlisting>
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would be sufficient for a gstreamer-only program.
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If (for example) your app also used GTK+ 2.0, you could use
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<programlisting>
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$ gcc `pkg-config --cflags --libs gstreamer-&GST_MAJORMINOR; gtk+-2.0` -o myprog myprog.c
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</programlisting>
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Those are back-ticks (on the same key with the tilde on US keyboards),
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not single quotes.
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</para>
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<para>
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For bigger projects, you should integrate pkg-config use in your Makefile,
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or integrate with autoconf using the pkg.m4 macro.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question id="developing-uninstalled-gstreamer">
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<para>How do I develop against an uninstalled GStreamer copy ?</para>
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</question>
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<answer>
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<para>
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It is possible to develop and compile against an uninstalled copy of
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gstreamer and gst-plugins (for example, against CVS copies).
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The easiest way to do this is to use a script like this (for bash):
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<programlisting>
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#!/bin/bash -i
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# set up environment to use and develop gstreamer from uninstalled
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# this is run -i so that PS1 doesn't get cleared
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# extract version from $0
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# gst-cvs -> cvs
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VERSION=`echo $0 | sed s/.*gst-//g`
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echo $VERSION
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# base path under which dirs are installed
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GST=~/gst/$VERSION
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if test ! -e $GST; then
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echo "$GST does not exist !"
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exit
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fi
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# set up a bunch of paths
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PATH=$GST/gstreamer/tools:$GST/gst-plugins/tools:$PATH
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export PKG_CONFIG_PATH=$GST/gstreamer/pkgconfig:$GST/gst-plugins/pkgconfig
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export GST_PLUGIN_PATH=$GST/gstreamer:$GST/gst-plugins
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# set up prompt to help us remember we're in a subshell and start bash
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PS1="[gst-$VERSION] $PS1" bash
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</programlisting>
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If you put this script in your path, and symlink it to gst-cvs (if you want
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to develop against cvs HEAD) or to gst-0.6 (if you want to develop against the
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0.6 branch), it will automatically use the uninstalled version from that
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directory.
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</para>
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<para>
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This requires you to have put your checkouts of gstreamer and gst-plugins
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under ~/gst/cvs (for the HEAD version). The program is easily modifiable
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if this isn't the case.
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</para>
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<para>
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After running this script, you'll be in an environment where you can
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use the uninstalled tools, and where gst-register registers the uninstalled
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plugins by default. Also, pkg-config wil detect the uninstalled copies
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before any installed copies.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question id="developing-gconf">
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<para>How can I use GConf to get the system-wide defaults ?</para>
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</question>
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<answer>
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<para>
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It's a good idea to use GConf to use default ways of outputting audio and
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video. Since GStreamer's GConf keys can be more than
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just one element, but a whole pipeline, it would be a good idea
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to use the gstgconf library. It provides functions to parse the GConf key
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to a usable pipeline.
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</para>
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<para>
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To link against gstgconf, use pkg-config to query the gstreamer-libs-&GST_MAJORMINOR;.pc file
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for link flags, and add -lgstgconf to the link flags.
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This fragment of configure.ac shows how to use pkg-config to get the LIBS:
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</para>
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<programlisting>
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dnl check for GStreamer helper libs
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PKG_CHECK_MODULES(GST_HELPLIBS, gstreamer-libs-&GST_MAJORMINOR; >= $GSTREAMER_REQ,,exit)
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AC_SUBST(GST_HELPLIBS_LIBS)
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AC_SUBST(GST_HELPLIBS_CFLAGS)
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</programlisting>
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<para>
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This fragment of a Makefile.am file shows how to make your application link
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to it:
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</para>
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<programlisting>
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bin_PROGRAMS = application
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application_LDADD = $(GST_LIBS) $(GST_HELPLIBS_LIBS) -lgstgconf
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application_CFLAGS = $(GST_CFLAGS) $(GST_HELPLIBS_CFLAGS)
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</programlisting>
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</answer>
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</qandaentry>
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<qandaentry>
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<question id="developing-libtool-scripts">
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<para>
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How do I debug these funny shell scripts that libtool makes ?
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</para>
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</question>
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<answer>
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<para>
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When you link a program against uninstalled GStreamer using libtool,
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funny shell scripts are made to modify your shared object search path
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and then run your program. For instance, to debug gst-launch, try
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<programlisting>
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libtool gdb /path/to/gstreamer-launch
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</programlisting>.
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If this does not work, you're probably using a broken version of libtool.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question id="developing-mail-gstreamer-devel">
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<para>Why is mail traffic so low on gstreamer-devel ?</para>
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</question>
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<answer>
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<para>
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Our main arena for coordination and discussion is IRC, not email.
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Join us in #gstreamer on irc.freenode.net
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For larger picture questions or getting more input from more persons,
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a mail to gstreamer-devel is never a bad idea.
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However, we do archive our IRC discussions, which you may find in the
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gstreamer-daily mailing list archives.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question id="developing-versioning">
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<para>What kind of versioning scheme does GStreamer use ?</para>
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</question>
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<answer>
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<para>
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For public releases, GStreamer uses a standard MAJOR.MINOR.MICRO version
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scheme. If the release consists of mostly bug fixes or incremental changes,
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the MICRO version is incremented.
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If the release contains big changes, the MINOR version is incremented.
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If we're particularly giddy, we might even increase the MAJOR number.
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Don't hold your breath for that though.
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</para>
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<para>
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During the development cycle, GStreamer also uses a fourth or NANO number.
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If this number is 1, then it's a CVS version.
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Any tarball or package that has a nano number of 1 is made from CVS and thus
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not supported. Additionally, if you didn't get this package or tarball from
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the GStreamer team, don't have high hopes on it doing whatever you want it
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to do.
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</para>
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<para>
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If the number is 2 or higher, it's an official pre-release in preparation
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of an actual complete release. Your help in testing these tarballs and
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packages is very much appreciated.
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</para>
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</answer>
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</qandaentry>
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<qandaentry>
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<question id="developing-coding-style">
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<para>What is the coding style for GStreamer core ?</para>
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</question>
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<answer>
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<para>
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The core is basically coded in K&R with 2-space indenting.
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Just follow what's already there and you'll be fine.
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The core could use a code cleanup though at this point.
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</para>
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<para>
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Individual plugins in gst-plugins or plugins that you want considered for
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addition to the gst-plugins module should be coded in the same style.
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It's easier if everything is consistent. Consistency is, of course, the goal.
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</para>
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<para>
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If you use emacs, try these lines:
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<programlisting>
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(defun gstreamer-c-mode ()
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"C mode with adjusted defaults for use with GStreamer."
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(interactive)
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(c-mode)
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(c-set-style "K&R")
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(setq c-basic-offset 2))
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(setq auto-mode-alist (cons '("gst.*/.*\\.[ch]$" . gstreamer-c-mode)
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auto-mode-alist))
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</programlisting>
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</para>
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<para>
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Or, run your code through
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<programlisting>
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indent -br -bad -cbi0 -cli2 -bls -l100 -ut -ce
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</programlisting>
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before submitting a patch (FIXME: check if these are indeed the proper options).
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</para>
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<para>
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As for the code itself, the
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<ulink url="http://developer.gnome.org/doc/guides/programming-guidelines/book1.html">GNOME coding guidelines</ulink> is a good read.
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Where possible, we try to adhere to the spirit of GObject and use similar
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coding idioms.
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</para>
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</answer>
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</qandaentry>
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</qandaset>
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</sect1>
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