# GEGL-0.2.0

## GEGL

GEGL (Generic Graphics Library) is a graph based image processing framework.

GEGL provides infrastructure to do demand based cached non destructive image editing on larger than RAM buffers. Through babl it provides support for a wide range of color models and pixel storage formats for input and output.

### Features

- Floating point handling and processing and output of larger 8bit, 16bit integer and 32bit floating point per component buffers larger than RAM.

- C, vala, C#, Python and Ruby interfaces using a consistent DOM like graph API to manage processing graphs.

- Processing

  - Iterative chunk-wise processing.

  - Processes subregions and dependencies.

  - Subgraph caches to aid performance of non-destructive editing.

  - Experimental OpenCL acceleration, with possibility of hybrid cpu/gpu processing.

- GeglBuffer

  - Storage of all babl supported formats.

  - Tiled sparse buffers (larger than RAM images).

  - linear buffers (allocated internally or from external allocation.)

  - On demand tiled mipmapping.

  - inter process shared storage

  - External tile-backends (allow wrapping other tiled buffer systems to use them through the GeglBuffer API).

- Operations

  - PNG, JPEG, SVG, EXR, RAW, ffmpeg, v4l and other image sources.

  - Pattern renderers

  - Arithmetic operations

  - link_operations.html#porter_duff[porter duff compositing]

  - SVG filter modes and full set of compositing ops from SVG-1.2 draft.

  - Gaussian blur, bilateral-filter, symmetric nearest neighbour, linear

  - blur, unsharp mask, pixelize and more.

  - Color correction.

  - Text rendering using cairo and pango.

  - HDR exposure merging and tone mapping operations.

  - Most operations operate in scRGB (using 32bit floating point/HDR linear light RGBA)

- Bounding box based hit detection.

- XML serialization format (not-finalized)

### News

This website is built at the time of the previous GEGL tarball release, for information about what might change on the way to the next release follow the following news sources:

Change log

  For day to day fixes, contributions and changes.

NEWS

  The NEWS file for a list of major new features (also contains older NEWS).

bugzilla

  for known and tracked issues with GEGL and perhaps see the

mail

  The mailinglist archives for some discussion and announcement.

### Gallery

For examples of what GEGL’s rendering engine currently can do look at the gallery.

### Bugzilla

The GEGL project uses GNOME Bugzilla, a bug-tracking system that allows us to coordinate bug reports. Bugzilla is also used for enhancement requests and the preferred way to submit patches for GEGL is to open a bug report and attach the patch to it. Bugzilla is also the closest you will find to a roadmap for GEGL.

Below is a list of links to get you started with Bugzilla:

- List of Open Bugs

- List of Open Bugs (excluding enhancement requests)

- List of Enhancement Proposals

- Bugzilla Weekly Summary

### Community

You can subscribe to gegl-developer and view the archives here. The GEGL developer list is the appopriate place to ask development questions, and get more information about GEGL development in general. You can email this list at gegl-developer-list@gnome.org.

GEGL development is also discussed in #gegl on GIMPnet (irc.gimp.org).

### Copyright

GEGL is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License and GNU General Public License as published by the Free Software Foundation; either version 3 of the Licenses, or (at your option) any later version. The library itself is licensed under LGPL while the sample commandline application and GUI binary gegl is licensed under GPL.

### Contributors

Many people have contributed to GEGL over time the following lists are are ordered chronologically according to when they are mentioned in the ChangeLog.

#### Code:

Calvin Williamson, Caroline Dahloff, Manish Singh, Jay Cox Daniel Rogers, Sven Neumann, Michael Natterer, Øyvind Kolås, Philip Lafleur, Dominik Ernst, Richard Kralovic, Kevin Cozens, Victor Bogado, Martin Nordholts, Geert Jordaens, Michael Schumacher, John Marshall, Étienne Bersac, Mark Probst, Håkon Hitland, Tor Lillqvist, Hans Breuer, Deji Akingunola and Bradley Broom, Hans Petter Jansson, Jan Heller, dmacks@netscpace.org, Sven Anders, Hubert Figuière, Sam Hocevar, yahvuu at gmail.com, Nicolas Robidoux, Ruben Vermeersch, Gary V. Vaughan, James Legg, Henrik Åkesson, Fryderyk Dziarmagowski, Ozan Caglayan, Tobias Mueller, Nils Philippsen, Adam Turcotte, Danny Robson, Javier Jardón and Yakkov Selkowitz, Kaja Liiv, Eric Daoust, Damien de Lemeny, Fabian Groffen, Vincent Untz, Debarshi Ray, Stuart Axon, Kao, Barak Itkin, Michael Muré, Mikael Magnusson, Patrick Horgan, Tobias Ellinghaus, Rasmus Hahn, Chantal Racette, John Cupitt, Anthony Thyssen, Emilio Pozuelo Monfort, Robert Sasu, Massimo Valentini, Hans Lo, Zbigniew Chyla, David Evans, Javier Jardón, Matteo F. Vescovi and Jan Rüegg.

#### Documentation:

Garry R. Osgood, Øyvind Kolås, Kevin Cozens and Shlomi Fish.

#### Artwork:

Jakub Steiner, Øyvind Kolås, Tonda Tavalec

## Building from source

GEGL and it’s dependencies are known to work on Linux based systems, windows with msys/mingw, and probably other platforms.

### Download

The latest development snapshot, and eventually stable versions of GEGL are available at ftp://ftp.gimp.org/pub/gegl/.

The current code under development can be browsed online and cloned from GNOME git using:

    $ git clone git://git.gnome.org/babl
    $ git clone git://git.gnome.org/gegl

### Dependencies

GEGL currently builds and works on linux, win32 and OSX most probably also on other systems where glib and gtk+ work.

- Core

  - glib (including gobject, and gmodule) 2.16 or newer, which provides inheritance, dynamic modules, common algorithms and data structures for C programming.

  - babl 0.0.22 or newer (for pixel-format agnostisism).

  - libpng (png load/export ops, and image magick fallback import)

  - ruby (only if building from git)

- GUI (sandbox for testing ops and the API)

  - GTK+

- Optional dependencies for operations.

  - SDL (display op)

  - libjpeg (jpg loader op)

  - libopenexr (exr loader op)

  - libopenraw (raw loader op)

  - cairo, pango (text source op)

  - avcodec, avformat (ff-load and experimental ff-save)

  - librsvg (svg loader)

- Documentation (this document)

  - asciidoc

### Compiling

To build GEGL type the following in the toplevel source directory:

    $ ./configure  # or: ./autogen.sh if building from git
    $ make
    $ sudo make install

## Documentation

With GEGL you chain together image processing operations represented by nodes into a graph. GEGL provides such operations for loading and storing images, adjusting colors, filtering in different ways, transforming and compositing images.

GEGL’s programmer/user interface is a Directed Acyclic Graph of nodes. The DAG expresses a processing chain of operations. A DAG, or any node in it, expresses a composited and processed image. It is possible to request rectangular regions in a wide range of pixel formats from any node.

## Development

This howto describes good-to-know things for developing gegl

### Public API

The public API reference documents the API used for creating things with GEGL, this API does not change much at all and is also the API provided by language bindings. To make the public API available when compiling a .c file add #include <gegl.h>, compile and link with the flags provided by pkg-config and you should be all set. When you are comfortable with the public API, or are using GEGL in some project looking at the Operation reference might be useful.

The public API also includes GeglBuffer, a flexible tiled and linear raster buffer storage system.

#### Bindings

The bindings for use of GEGL in other programming languages than C are co-hosted with GEGL in GNOME git but are not part of the regular GEGL distribution. The following language bindings are currently available:

vala, C#, Python and Ruby.

#### Hello world

The following is a small sample GEGL application that animates a zoom on a mandelbrot fractal. compile it with:

    $ gcc hello-world.c `pkg-config --libs --cflags gegl` -o hello-world

This example and others can be found in the examples subdir of the GEGL distribution.

    #include <gegl.h>
    #include <glib/gprintf.h>

    gint
    main (gint    argc,
          gchar **argv)
    {
      g_thread_init (NULL);
      gegl_init (&argc, &argv);  /* initialize the GEGL library */

      {
        /* instantiate a graph */
        GeglNode *gegl = gegl_node_new ();

    /*
    This is the graph we're going to construct:

    .-----------.
    | display   |
    `-----------'
       |
    .-------.
    | over  |
    `-------'
       |   \
       |    \
       |     \
       |      |
       |   .------.
       |   | text |
       |   `------'
    .------------------.
    | fractal-explorer |
    `------------------'

    */

        /*< The image nodes representing operations we want to perform */
        GeglNode *display    = gegl_node_create_child (gegl, "gegl:display");
        GeglNode *over       = gegl_node_new_child (gegl,
                                     "operation", "gegl:over",
                                     NULL);
        GeglNode *text       = gegl_node_new_child (gegl,
                                     "operation", "gegl:text",
                                     "size", 10.0,
                                     "color", gegl_color_new ("rgb(1.0,1.0,1.0)"),
                                     NULL);
        GeglNode *mandelbrot = gegl_node_new_child (gegl,
                                    "operation", "gegl:fractal-explorer",
                                    "width", 512,
                                    "height", 384,
                                    NULL);

        gegl_node_link_many (mandelbrot, over, display, NULL);
        gegl_node_connect_to (text, "output",  over, "aux");

        /* request that the save node is processed, all dependencies will
         * be processed as well
         */
        {
          gint frame;
          gint frames = 200;

          for (frame=0; frame<frames; frame++)
            {
              gchar string[512];
              gdouble t = frame * 1.0/frames;
              gdouble cx = -1.76;
              gdouble cy = 0.0;

    #define INTERPOLATE(min,max) ((max)*(t)+(min)*(1.0-t))

              gdouble xmin = INTERPOLATE(  cx-0.02, cx-2.5);
              gdouble ymin = INTERPOLATE(  cy-0.02, cy-2.5);
              gdouble xmax = INTERPOLATE(  cx+0.02, cx+2.5);
              gdouble ymax = INTERPOLATE(  cy+0.02, cy+2.5);

              if (xmin<-3.0)
                xmin=-3.0;
              if (ymin<-3.0)
                ymin=-3.0;

              gegl_node_set (mandelbrot, "xmin", xmin,
                                         "ymin", ymin,
                                         "xmax", xmax,
                                         "ymax", ymax,
                                         NULL);
              g_sprintf (string, "%1.3f,%1.3f %1.3f×%1.3f",
                xmin, ymin, xmax-xmin, ymax-ymin);
              gegl_node_set (text, "string", string, NULL);
              gegl_node_process (display);
            }
        }

        /* free resources used by the graph and the nodes it owns */
        g_object_unref (gegl);
      }

      /* free resources globally used by GEGL */
      gegl_exit ();

      return 0;
    }

### Operation API

An API to extend the functionality of GEGL with new image processing primitive, file loaders, export formats or similar.

Each GEGL operation is defined in a .c file that gets turned into a single shared object that is loaded. Each operation is a subclass of one of the provided base classes:

GeglOperation

  The base operation class, which all the other base classes are derived from, deriving from this is often quite a bit of work and is encouraged only when your operation doesn’t fit into any of the other categories

GeglOperationFilter

  The filter base class sets up GeglBuffers for input and output pads

GeglOperationPointFilter

  The point-filter base class is for filters where an output pixel only depends on the color and alpha values of the corresponding input pixel. This allows you to do the processing on linear buffers, in the future versions of GEGL operations implemented using the point-filter will get speed increases due to more intelligent processing possible in the point filter class

GeglOperationAreaFilter

  The AreaFilter base class allows defining operations where the output data depends on a neighbourhood with an input window that extends beyond the output window, the information about needed extra pixels in different directions should be set up in the prepare callback for the operation.

GeglOperationComposer

  Composer operations are operations that take two inputs named input and aux and write their output to the output pad output

GeglOperationPointComposer

  A baseclass for composer functions where the output pixels' values depends only on the values of the single corresponding input and aux pixels.

GeglOperationSource

  Operations used as render sources or file loaders, the process method receives a GeglBuffer to write it’s output into

GeglOperationPointRender

  The point-render base class is a specialized source operation, where the render is done in small piece to lower the need to do copies. It’s dedicated to operation which may be rendered in pieces, like pattern generation.

GeglOperationSink

  An operation that consumes a GeglBuffer, used for filewriters, display (for the sdl display node)

GeglOperationTemporal

  Base class for operations that want access to previous frames in a video sequence, it contains API to configure the amounts of frames to store as well as getting a GeglBuffer pointing to any of the previously stored frames.

GeglOperationMeta

  Used for GEGL operations that are implemented as a sub-graph, at the moment these are defined as C files but should in the future be possible to declare as XML instead.

To create your own operations you should start by looking for one that does approximatly what you already need. Copy it to a new .c source file, and replace the occurences of the filename (operation name in the source.)

Take a look at the brightness contrast operation for a point operation well sprinkled with comments as a starting point.

### Environment

Some environment variables can be set to alter how GEGL runs, all of these options are also available as properties on a singleton GObject returned from gegl_config ().

GEGL_QUALITY

  A value between 0.0 and 1.0 indicating a trade-off between quality and speed. Defaults to 1.0 (max quality).

BABL_TOLERANCE

  The amount of error that babl tolerates, set it to for instance 0.1 to use some conversions that trade some quality for speed.

GEGL_CHUNK_SIZE

  The number of pixels processed simulatnously.

GEGL_TILE_SIZE

  The tile size used internally by GEGL, defaults to 128x64

GEGL_SWAP

  The directory where temporary swap files are written, if not specified GEGL will not swap to disk. Be aware that swapping to disk is still experimental and GEGL is currently not removing the per process swap files.

GEGL_CACHE_SIZE

  The size of the tile cache used by GeglBuffer specified in megabytes.

GEGL_DEBUG

  set it to "all" to enable all debugging, more specific domains for debugging information are also available.

BABL_STATS

  When set babl will write a html file (/tmp/babl-stats.html) containing a matrix of used conversions, as well as all existing conversions and which optimized paths are followed.

GEGL_DEBUG_BUFS

  Display tile/buffer leakage statistics.

GEGL_DEBUG_RECTS

  Show the results of have/need rect negotiations.

GEGL_DEBUG_TIME

  Print a performance instrumentation breakdown of GEGL and it’s operations. GEGL_USE_OPENCL: Enable use of OpenCL processing.

### gegl

GEGL provides a commandline tool called gegl, for working with the XML data model from file, stdin or the commandline. It can display the result of processing the layer tree or save it to file.

Some examples:

Render a composition to a PNG file:

    $ gegl composition.xml -o composition.png

Invoke gegl like a viewer for gegl compositions:

    $ gegl -ui -d 5 composition.xml

Using gegl with png’s passing through stdin/stdout piping.

    $ cat input.png | gegl -o - -x "<gegl>
       <tree>
         <node class='invert'/>
         <node class='scale' x='0.5' y='0.5'/>
         <node class='png-load' path='-'/></tree></gegl>" > output.png

The latest development version is available in the gegl repository in GNOME git.

#### gegl usage

The following is the usage information of the gegl binary, this documentation might not be complete.

## Appendixes

### Operations

The main source of documentation as GEGL grows is the operations reference. Plug-ins themselves register information about the categories they belong to, what they do, and documentation of the available parameters.

### Glossary

connection

  A link/pipe routing image flow between operations within the graph goes from an output pad to an input pad, in graph glossary this might also be referred to as an edge.

DAG

  Directed Acyclic Graph, see graph.

graph

  A composition of nodes, the graph is a DAG.

node

  The nodes are connected in the graph. A node has an associated operation or can be constructed graph.

operation

  The processing primitive of GEGL, is where the actual image processing takes place. Operations are plug-ins and provide the actual functionality of GEGL

pad

  The part of a node that exchanges image content. The place where image "pipes" are used to connect the various operations in the composition.

input pad

  consumes image data, might also be seen as an image parameter to the operation.

output pad

  a place where data can be requested, multiple input pads can reference the same output pad.

property

  Properties are what controls the behavior of operations. Through the use of GParamSpecs properties they are self documenting via introspection.

### Directory overview

#### GEGL dirs

Directories marked with ⊙ use GNU make extensions to include any .c file dropped into the directory in the build.

    gegl-dist-root
     │
     │
     ├──gegl               core source of GEGL, library init/deinit,
     │   │
     │   ├──buffer         contains the implementation of GeglBuffer
     │   │                  - sparse (tiled)
     │   │                  - recursivly subbuffer extendable
     │   │                  - clipping rectangle (defaults to bounds when making
     │   │                    subbuffers)
     │   │                  - storage in any babl supported pixel format
     │   │                  - read/write rectangular region as linear buffer for
     │   │                    any babl supported pixel format.
     │   ├──graph          graph storage and manipulation code.
     │   ├──module         The code to load plug-ins located in a colon seperated
     │   │                 list of paths from the environment variable GEGL_PATH
     │   ├──operation      The GeglOperation base class, and subclasses that act
     │   │                 as baseclasses for implementeting different types of
     │   │                 operation plug-ins.
     │   ├──process        The code controlling data processing.
     │   └──property-types specialized classes/paramspecs for GeglOperation
     │                     properties.
     │
     ├──examples ⊙        hello-world and other example uses of the GEGL API.
     │
     ├──tests             various tests used to maintain stability when developing
     │                    GEGL.
     │
     ├──operations        Runtime loaded plug-ins for image processing operations.
     │   │
     │   ├──core ⊙        Basic operations tightly coupled with GEGL.
     │   ├──affine        Transforming operations (rotate/scale/translate)
     │   ├──generated ⊙   Operations generated from scripts (currently
     │   ├──external      Operations with external dependencies.
     │   ├──common ⊙      Other operations.
     │   └──workshop ⊙    Works in progress, (you must pass --enable-workshop
     │       │            when configurig to build these by default, you can enter
     │       │            the directory manually and type make && sudo make install
     │       │            as well.
     │       │
     │       ├──external  operations in the workshop with external dependencies.
     │       └──generated generated operations that are in the workshop.
     │
     │
     ├──docs              The GEGL website (this documentation), built for your
     │   │                the corresponding sourcetree with correct documentation
     │   │                etc.
     │   │
     │   └──gallery ⊙     A gallery of sample GEGL compositions, using the
     │       │            (not yet stabilized) XML format.
     │       │
     │       └──data      Image data used by the sample compositions.
     │
     ├──bin               gegl binary, for processing XML compositions to png files.
     │
     ├──bindings          bindings for using GEGL from other programming languages
     │                    not included in the tarball distribution but exist in
     │                    the git repository.
     │
     └──tools             some small utilities to help the build.