Chapter 2. Actors

An actor's a guy who if you ain't talkin' about him, ain't listening.

Edmon Gween, actor, on his deathbed

1. Introduction

When building a User Interface with Clutter, the visible part of the UI — that is, what is displayed on the screen — is commonly referred to as "the scene graph". Like every graph, a scene graph is composed by nodes.

Every node on the Clutter scene graph is an actor. Every actor has a single relationship with the others: it can be the parent of another actor, or a child of another actor.


The stage is an actor that can have children but cannot have any parent.

Actors have different attributes: a position, a size, a scale factor, a rotation angle on each axis (relative to a specific center on the normal plane for that axis), an opacity factor.

The scene graph is not fixed: it can be changed, not only by adding or removing actors, but also by changing the parent-child relationship: it is possible, for instance, to move an entire section of the scene graph from one parent actor to another.