# Glossary

actor

  An item on the scenegraph. Every actor has a parent, except the stage, and some actors can be containers. Every actor has a geometry and, when visible, it should paint its contents. The base class for actors is #ClutterActor.

allocation

  The final size of an actor within its parent. For example, an actor might have a preferred minimum size of 20×20 pixels and a natural size of 40×40 pixels, but its parent may decide to allocate 50×20 pixels for it instead.

  minimum size natural size
child

  A container's child is an actor contained inside it.

container

  An actor which can contain other actors. If a container is meant to be extended using public API it should implement the #ClutterContainer interface; otherwise it is a composite actor. A container can let its children manage their geometry, like #ClutterGroup, or they can take care of assigning one.

event

  Events are the way in which the Clutter backend informs Clutter about external events like pointer motion, button clicks, key presses, etc.

geometry

  An actor's position and size. A geometry can be expressed in actor-relative untransformed coordinates; or in stage-relative, transformed coordinates.

minimum size

  The minimum, useful size of an actor. For instance, a button might have a minimum size of 20×20 millimeters on a touch screen, to retain the ability for the user to press it. A container that manages the size of its children should always try to allocate at least their minimum size.

  natural size allocation
natural size

  The default size requested by an actor.

  minimum size allocation
parent

  An actor's parent is the container inside which the actor resides.

scenegraph

  The tree of all actors, starting from the stage at the root and following the containers.

stage

  The top-level container for actors. Depending on the Clutter back end a stage can be associated to a window or to a frame buffer; also depending on the back end is the number of instantiatable stages. Stages in Clutter can be manipulated using the #ClutterStage API.

transformation

  A rotation, scaling or traslation of an actor. Transformations are independent of the actor's geometry.