G?GL application level API glossary

G?GL

A graph oriented image processing API.

graph

A composition of nodes, the graph is a DAG.

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 reffered to as an edge.

operation

The processing primitive of G?GL, it is where the actual image processing takes place. Documentation for extending the image processing capabilities has not been written yet. Various names exist for operations depending on their number of input- and output pads.

composer

A operation that has more than one input pad.

samples:

• porter duff composition operators (over, in, atop, under ...)
• apply opacity mask
• merging of grayscale R,G and B buffers into a color image (a treebased view of compositing doesn't have a natural place for composers with more than two input pads, it is possible to express this operation by having a set_component operation, that replaces one component in-line.)

decomposer

A operation that has more than one output pad. decomposer nodes are not expressable in a treeview and are restricted to the graph portion of the oxide file format.

samples:

• split an image into seperate grayscale component buffers. (NOTE: a more general practice that works well in a tree based compositor is two operations, one that converts to a given sample model and one that extracts a given band.)

filter

A operation that has one input pad and one output pad.

samples:

• color correction
• blur
• perlin noise

source

A operation that only has one output pad

samples:

• png loader
• video frame loader
• blank image
• svg rasterizer
• text rasterizer
• webcam feed

sink

A operation that only has one input pad

samples:

• still image file output (png)
• display in gtk+ widget
• display in toplevel x window
• in memory buffer
• video frame writer

node

Synomnym for operation, node is a graph oriented glossary, whilst operation speak of an image operation, that does something with image samples.

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 control the behavior of operations, properties are named, have defined types and ranges, and probably provide hints about their usage. e.g. a string can be (amongst other things) a file parameter or font defintion, both should be handled differenlty in an autogenerated UI.).

misc

DAG

Directed Acyclic Graph, graphviz is a nice application for drawing them

active op

An operation that is active in the graph, an active op will be processed when the graph is processed, all op's the active op depends on will also be processed (name pending change, currently only used in gggl since GEGL doesn't support multiple roots (yet)