Development
===========

image::images/GEGL.png[GEGL]
*#Development#*

This document describes some handy things to know when developing the gegl internals.
Parts of it is copy-paste of emails on the gegl developer list.

== Setting up

=== Ubuntu 8.10
Setup instructions for Ubuntu 8.10 Intrepid Ibex

To install the mandatory dependencies:

 $ sudo apt-get install libtool automake glib libglib2.0-dev libpng12-dev libgtk2.0-dev git

Some of the other dependencies:

 $ sudo apt-get install asciidoc enscript libjpeg62 libopenraw graphviz-dev

For running gegl the GEGL_PATH, which is used for dynamically loading the 
operations, has to be set:

 $ export GEGL_PATH=~/Dev/gegl-dev/operations/

=== BABL

When using a development version of babl, gegl has to know from where to get it.
This is done by setting the BABL_LIBS environment variable before (or during
as shown below) running gegl's autogen.sh:

 $ ./autogen.sh BABL_LIBS=~/Dev/babl/babl/.libs/libbabl-0.0.so.0.23.0 CFLAGS="-O0"

Then when running the program, the babl library automatically loads extensions
that are either located in the BABL_HOME directory or in the default installation
directory, in mentioned order of preference.

 $ export BABL_HOME=~/Dev/babl/extensions

=== Netbeans 6.5

There are some key points to consider when setting up GEGL in an IDE
(tested on Netbeans):

- have to configure the IDE to use the autogen.sh as configure script
- normally have to use gegl/bin/.libs/gegl as the executable,
 not gegl/bin/gegl which is a script.
- in some (?) case has to use bin/.libs/lt-gegl as the executable, which is some
 kind of relinked gegl binary

== Debugging

By default gegl and babl uses the flag -g for debug instrumentation, but however
it doesn't use the -O0 flag for turning off optimisations. This leads to unexpected
jumps in the code when stepping in a debugger. You have to feed this flag to
autogen:

 $ ./autogen.sh CFLAGS="-O0"
 $ make

=== Debug output

GEGL has built in mechanisms for logging debug information.

 GEGL_NOTE (CACHE, "foo %s", bar);
 GEGL_TIMESTAMP(PROCESSOR);
 GEGL_MARK()

Where CACHE and PROCESSOR is used the following logging domains are available:

 PROCESS, CACHE, BUFFER_LOAD, BUFFER_SAVE, TILE_BACKEND and PROCESSOR

Actual printing of these can be enabled by setting the GEGL_DEBUG
environment variable like:

 GEGL_DEBUG=processor,cache

or even

 GEGL_DEBUG=all

There are also a few functions that are useful as you debug from
within a debugger such as GDB. In GDB for example, you call a function
interactively in the prompt, while a breakpoint is hit for example, by
typing

  print function_name(args)

Some useful functions are:

* *gegl_dot_node_to_png_default()* Writes a PNG to /tmp/node.png with
  the dependency graph for the passed node
* *gegl_node_dump_depends_on()* Dumps to stdout the nodes that the
  passed node depends on. With this you can work yourself backwards in
  a dependency graph.
* *gegl_node_get_debug_name()* Prints a debug string representation of
   a node.

=== Graphviz export
The gegl library has a utility that permits to export the DAG into a graphviz
format. Graphviz is a library that converts graph descriptions in textual format
into an image. See http://www.graphviz.org/[graphviz website]

It is done using:

 #include "../gegl/gegl-dot.h"
 /* for printing the dot output, note that gegl_node is a GeglNode pointer */
 gchar *dot_output = gegl_to_dot( gegl_node );
 printf( "%s\n", dot_output );
 g_free( dot_output );

For creating the graph image:

 $ gegl --file gaussian-blur.xml --output out.png | dot -Tpng > gb.png

This is the gaussian-blur.xml file:

 <?xml version='1.0' encoding='UTF-8'?>
 <gegl>
 	<node operation='gegl:gaussian-blur'>
 		<params>
 			<param name='std-dev-x'>0.999</param>
 			<param name='std-dev-y'>0.999</param>
 		</params>
 	</node>
 	<node operation='gegl:load'>
 		<params>
 			<param name='path'>in.png</param>
 		</params>
 	</node>
 </gegl>

link:images/gaussian-blur-graph.png[Resulting graph].

You can also just call the function gegl_dot_node_to_png() directly
from within gdb to show the graphviz graph of a node and its
dependencies.

== Tests

There are regression tests in the subfolder `tests`. These are run
with `make check`

=== Composition tests

The tests under `tests/compositions` are easy-to-write high-level
system tests for GEGL and its operations. Together with our
http://gimptest.flamingtext.com:8080/job/gegl-distcheck/[Jenkins
server] that runs all our tests each night, the composition tests make
a powerful framework for detecting regressions.

==== Adding a composition test

To add a composition test for a operation called `gegl:new-operation`,
do the following:

. Create a GEGL XML file `tests/compositions/new-operation.xml` (will
  typically look approximately like `tests/compositions/pixelise.xml`)
. Produce a reference image: `cd tests/compositions; gegl -o
  /tmp/new-operation.png new-operation.xml` (make sure your operation
  is installed so `gegl` finds it)
. Manually inspect the reference image `/tmp/new-operation.png` and
  move it to `tests/compositions/reference` if it looks like you expect
. Add `run-new-operation.xml.sh` to the `TESTS` variable in
  `tests/compositions/Makefile.am`
. Run `make check` in `tests/compositions` to verify that your test
  works (note that you must have configured GEGL with `autogen.sh` in
  order for your change to the `TESTS` variable to be taken into
  account)

And you're done. Do not manually create `run-new-operation.xml.sh`, it
will be created automatically for you during build time. It will run
`gegl` with `tests/compositions/new-operation.xml` and compare the
result with `tests/compositions/reference/new-operation.png`. If the
result differs, the test will fail, and mails will be sent to the GEGL
maintainers. As stated above, this test will run each night, so if
someone breaks your contributed GEGL operation, it will be discovered
at most 24 hours later, making it easy to fix, either by reverting the
bogus commit or by adjusting it.

An example of a commit that adds a composition test for a GEGL
operation is
http://git.gnome.org/browse/gegl/commit/?id=13e17712529fb714edcfd67e559bf46b622ff31d[Add
composition test for gegl:gamma].

== Documentation

This document describes how to document GEGL using it's build system.

There are three utilities used:

. http://www.methods.co.nz/asciidoc/[asciidoc] - used for generating html from text files
. http://www.codento.com/people/mtr/genscript/[enscript] - used for converting source files (.c/.h) to html
. a home-made ruby script - used for generating api documentation (not yet documented here)

All documentation resources are placed in /doc and the generation is controlled by the file Makefile.am

=== asciidoc

This example will show how this howto was added.

- Add in `Makefile.am` a new target named `documentation-howto.html` in
the existing list of html files to generate:

  if HAVE_ASCIIDOC
  	HTML_FILES += index.html documentation-howto.html
  endif

- Add in `Makefile.am` the target:

 documentation-howto.html: documentation-howto.txt
 if HAVE_ASCIIDOC
 	@echo "HTML: $@"
 	cp $< $@
 	$(ASCIIDOC) --unsafe  -o $@ -a stylesdir=`pwd` -a toc -a theme=gegl -a quirks! $<
 else
 	@echo "*** asciidoc must be available in order to make dist"
 	@false
 endif

- Create a new `documentation-howto.txt` file with this content:

 == Documentation howto

 This document describes how to document GEGL using it's build system.

- Type `make` and the `documentation-howto.txt` will be converted into `documentation-howto.html`

=== enscript

TODO
This example will show how a new c/h file is converted into html using enscript

== Inheritance tree

Here is an automatically generated inheritance tree of the gobjects used by gegl:
link:images/inheritance.png[GEGL inheritance tree]
Note that the operations are also gobjects, but they are not included in the inheritance tree.