DecalGroups

• DecalGroup extends OrderedGroup and renders children in order

  • Children must be co-planar

  • First child is the underlying surface

  • The underlying surface must encompass all other children

  • Use for rendering decal geometry

    • Text

    • Texture Decals (eg, insignia on an airplane wing)

• DecalGroup adds no additional methods beyond those of the OrderedGroup class

   Shape3D encompass = new Shape3D( geom, app );
   Shape3D decal1 = new Shape3D( geom1, app1 );
   Shape3D decal2 = new Shape3D( geom2, app2 );
   . . .
   DecalGroup decals = new DecalGroup( );
   decals.addChild( encompass );
   decals.addChild( decal1 );
   decals.addChild( decal2 );

The DecalGroup node is a subclass of the OrderedGroup node. The DecalGroup node is an ordered group node used for defining decal geometry on top of other geometry. The DecalGroup node specifies that its children should be rendered in index order and that they generate coplanar objects. Examples include painted decals or text on surfaces and a checkerboard layered on top of a table.

The first child, at index 0, defines the surface on top of which all other children are rendered. The geometry of this child must encompass all other children; otherwise, incorrect rendering may result. The polygons contained within each of the children must be facing the same way. If the polygons defined by the first child are front facing, then all other surfaces should be front facing. In this case, the polygons are rendered in order. The renderer can use knowledge of the coplanar nature of the surfaces to avoid Z-buffer collisions. (If, for example, the underlying implementation supports stenciling or polygon offset, then these techniques may be employed.) If the main surface is back facing, then all other surfaces should be back facing and need not be rendered (even if back-face culling is disabled).

Note that using the DecalGroup node does not guarantee that Z-buffer collisions are avoided. An implementation of Java 3D may fall back to treating DecalGroup node as an ordinary OrderedGroup node.