GEGL 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.  Take a look at
link:brightness-contrast.c.html[the brightness contrast operation] for a point
operation well sprinkled with comments as a starting point.  Each operation is
a subclass of one of the provided base classes:

link:gegl-operation.h.html[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
link:gegl-operation-filter.h.html[GeglOperationFilter]::
    The filter base class sets up GeglBuffers for input and output pads

link:gegl-operation-point-filter.h.html[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

link:gegl-operation-area-filter.h.html[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.

link:gegl-operation-composer.h.html[GeglOperationComposer]::
    Composer operations are operations that take two inputs named 'input' and
    'aux' and write their output to the output pad 'output'

link:gegl-operation-point-composer.h.html[GeglOperationPointComposer]::
    A baseclass for composer functions where the output pixels' values depends
    only on the values of the single corresponding input and aux pixels.

link:gegl-operation-source.h.html[GeglOperationSource]::
    Operations used as render sources or file loaders, the process method
    receives a GeglBuffer to write its output into

link:gegl-operation-point-render.h.html[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.

link:gegl-operation-sink.h.html[GeglOperationSink]::
    An operation that consumes a GeglBuffer, used for filewriters, display (for
    the sdl display node)

link:gegl-operation-temporal.h.html[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.

link:gegl-operation-meta.h.html[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.)
