Extensions to Gn

To provide the features of reflection, transparency with refraction, and CSG operations, the following additions were made to the Gn specification of gn_model:

• Geometry csg_difference Modelname1 Modelname2
  A csg_differenceobject applies the CSG difference operator by subtracting the second model from the first.

• Geometry csg_intersection Modelname1 Modelname2
  A csg_intersectionobject applies the CSG intersection operator to the two objects so that only their overlapping parts are kept.

• Option -reflective_factor float
  Defaults to 0. Specifies the factor by which an object reflects light rays. This is an attenuation factor of the intensity of the reflected light ray.

• Option -transparency_factor float
  Defaults to 0. Specifies the amount of light which is allowed to pass through the object surface. A value of 0 specifies an opaque object; a value of 1 specifies a completely transparent object.

• Option -refractive_index float
  Defaults to 1. Specifies the factor by which a transparent object bends light rays. A value of 1 allows the light ray to pass through without being bent, while higher values provide refraction similar to real materials (i.e., glass 1.52, diamond 2.419).

To provide the solid texture mapping features, the following extensions were made to the Gn specification of gn_material:

• Lightingmodel solid_texture
  Defaults to the wood grain texture map. Allows the user to choose a predefined texture map function. The user may choose a specific texture map with the -texture_map option.

• Option -texture_map map_function
  Specifies the texture map function to be used for the solid_texture light model. The possible choices for the map_functionare wood_grain and stone.