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CHAPTER 9                                                           Multimedia Features



The O entry describes the opacity to be used when rendering this node, and the V
entry determines whether or not the node is rendered at all. While a node with an
opacity of 0 is rendered in the same way as a non-visible node, having a separate
value for the visibility of a node allows interactive viewer applications to show/
hide partially transparent nodes, without overwriting the intended opacity of
those nodes.

The M entry specifies the node’s matrix relative to its parent, in world coordi-
nates. If an hierarchy of nodes is intended to be repositioned while still maintain-
ing its internal structure, then only the node at the root of the hierarchy needs to
be adjusted.

Example 9.4 shows a 3D view specifying an array of node parameters.

Example 9.4
   3 0 obj            % Default node params with all shapes visible and opaque
   [ << /Type /3DNode
          /N (Sphere)
          /O 1
          /V true
          /M [...]>>
       << /Type /3DNode
          /N (Cone)
          /O 1
          /V true >>
       << /Type /3DNode
          /N (Cube)
          /O 1
          /V true >>
   ]

   4 0 obj            % Params with the cone hidden and the sphere semi-transparent
   [ << /Type /3DNode
          /N (Sphere)
          /O 0.5
          /V true >>
       << /Type /3DNode
          /N (Cone)
          /O 1
          /V false >>
       << /Type /3DNode
          /N (Cube)

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