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A scene graph is a general data structure commonly used by vector-based graphics editing applications and modern computer games, which arranges the logical and often (but not necessarily) spatial representation of a graphical scene. Examples of such programs include Acrobat 3D, Adobe Illustrator, AutoCAD, CorelDRAW, OpenSceneGraph, OpenSG, VRML97, X3D, Hoops and Open Inventor. A scene graph is a collection of nodes in a graph or tree structure. A tree node (in the overall tree structure of the scene graph) may have many children but often only a single parent, with the effect of a parent applied to all its child nodes; an operation performed on a group automatically propagates its effect to all of its members. In many programs, associating a geometrical transformation matrix (see also transformation and matrix) at each group level and concatenating such matrices together is an efficient and natural way to process such operations. A common feature, for instance, is the ability to group related shapes/objects into a compound object that can then be moved, transformed, selected, etc. as easily as a single object. It also happens that in some scene graphs, a node can have a relation to any node including itself, or at least an extension that refers to another node (for instance Pixar's PhotoRealistic RenderMan because of its usage of Reyes rendering algorithm, or Adobe Systems's Acrobat 3D for advanced interactive manipulation). The term scene graph is sometimes confused with Canvas (GUI), since some canvas implementations include scene graph functionality. ==Scene graphs in graphics editing tools== In vector-based graphics editing, each leaf node in a scene graph represents some atomic unit of the document, usually a shape such as an ellipse or Bezier path. Although shapes themselves (particularly paths) can be decomposed further into nodes such as spline nodes, it is practical to think of the scene graph as composed of shapes rather than going to a lower level of representation. Another useful and user-driven node concept is the layer. A layer acts like a transparent sheet upon which any number of shapes and shape groups can be placed. The document then becomes a set of layers, any of which can be conveniently made invisible, dimmed, or locked (made read-only). Some applications place all layers in a linear list, while others support sublayers (i.e., layers within layers to any desired depth). Internally, there may be no real structural difference between layers and groups at all, since they are both just nodes of a scene graph. If differences are needed, a common type declaration in C++ would be to make a generic node class, and then derive layers and groups as subclasses. A visibility member, for example, would be a feature of a layer, but not necessarily of a group. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Scene graph」の詳細全文を読む スポンサード リンク
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