Environment
~~~~~~~~~~~
Some environment variables can be set to alter how GEGL runs, these options are
also available as properties on a singleton GObject returned from gegl_config
(). The defaults should be what one normally uses - overriding 

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 simultanously.
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.
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_PATH:
    The directory where GEGL looks (recursively) for loadable operations,
    setting it to GEGL_PATH=/home/user/where_you_keep_src/gegl/operations
    permits running an application against the operations in the source dir
    instead of having to install the operations.
BABL_PATH:
    The directory containing babl extensions, both new pixel formats/color
    models as well as fast-paths for efficient pixel format conversions.
