The optional VideoLab(tm) video option board can be used in conjunction with
PowerVision systems to render real-time anti-aliased images. This board is capable of
converting the frame buffer image into NTSC or PAL signals in real-time. These
signals are roughly one quarter the resolution of the high-resolution frame buffer.
Special pixel averaging hardware uses a user programmable 3x3 or 2x2 filter function
to generate the NTSC and PAL signals.
3.3.14 Lighting Features
The PowerVision architecture supports a wide range of lighting capabilities to enable
the realistic rendering, of geometric primitives. Lighting effects are computed on a per-
vertex basis (Phong lighting) and are thus supported in the Geometry Engines.
PowerVision systems support all the following Graphics Library lighting capabilities
Up to eight light sources may be used simultaneously. The user can specify the color
and position of each light source. The PowerVision architecture supports spotlights
where the concentration of the spotlight is user controllable.
The Graphics Library allows the user to configure a number of surface properties to
achieve a high degree of realism. Specifically, the user can define the emissivity of a
surface and its ambient, diffuse, specular reflectivity, and transparency coefficients. A
shininess coefficient is provided to specify how shiny or dull an object is. The
Command Processor and Geometry Engines were specifically designed so that
surface properties can be modified on a per-vertex basis very quickly. This feature is
particularly useful for scientific visualization. For example, an aeronautical engineer
can change the diffuse reflectance at every vertex to show the stress contour across an
The user can specify different surface properties for the front and back sides of
geometric primitives. The user can use this feature to display objects whose inside
and outside colors differ without having to specify and render two separate
Local Light and Viewer Positioning
Traditionally, hardware-supported lighting models assume that the viewer and light
sources are positioned infinitely far from the object being illuminated. Although the
positioning of the viewer and/or light sources at a finite distance from the object can
enhance the realism of the scene, they are often avoided because of costly inverse
square root operations. The PowerVision Geometry Engines include special VLSI
support for computing inverse square roots, making local lighting calculations