mental ray supports input of surfaces defined by polygonal geometry. In the general case it allows to specify a list of arbitrary polygons (convex or concave) with optional holes using any number of vertices and edges. The polygons may be connected by shared vertices to form a mesh. Materials can be assigned to the whole mesh or per polygon. It is possible to attach any kind of extra data on a per vertex basis, like texture coordinates or user values. The source description of polygon surfaces is subject to tessellation and displacement for rendering.
Many applications perform all steps of modelling operations down to the creation of surface geometry including final tessellation for rendering engines. mental ray supports direct input of such tessellated geometry into its scene database as primitive lists, which avoids additional efforts for storage and tessellation of typically large intermediate data. For convenience, this type of geometry also supports sub-pixel displacement during rendering, which further tessellates the input faces as needed.
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