The Scene Graph and Transformations

We support a hierarchical scene graph for defining a 3D scene. We define the Node to be the basic building block. Currently a node may be a:

  • Group

  • Mesh

  • Light

All nodes inherit the transform (coordinate space) of their parent.

Groups define a set of children nodes, and a coordinate space which all children nodes inhabit.

The complete order of transformations within a Group node is the following:

  • Inherited transform from parent

  • Local (bind) transform from scene graph

  • Deformation transforms

    • Translation

    • Rotation (around X-axis, followed by Y-axis and finally Z-axis)

    • Scaling

Meshes and Lights are leaf nodes.

Meshes define:

  • Geometry

  • Material information related to portions of the geometry.

Lights may be one of 2 types:

  • Directional, best used for modelling distant constant light sources, such as the sun

  • Point (or omni-directional) lights, best used for lights that emanate from a position, such as a lamp, etc.

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