Apparatus for and method of converting height fields into parametric texture maps

Abstract

A graphics system that employs parametric texture maps that are converted from height fields. The system samples a hemisphere equidistantly to produce an array of normals, approximates a dot product of each sampled normal with an arbitrary unit vector, transforms the polynomials back to canonical basis, converts a height field to normals, and for each normal in the height field determines coefficients for a parametric texture map. The system then evaluates a diffuse contribution using the parametric texture map coefficients. The system may also then evaluate a specular contribution using the parametric texture map coefficients. The graphics system renders surface features of a 3D object in a manner that is direction dependent but without the time consuming and expensive calculations involved in the evaluation of lighting equations on a per pixel basis. A parametric texture map holds a set of parameters that define a surface structure in a manner in which the appearance of the surface structure varies in response to a direction vector. The direction vector may be any user-defined vector including a light source vector or a half-angle vector. The parameters are those of a predetermined equation, the evaluation of which does not involve vector calculations. The equation may take any form including a polynomial equation or a non-polynomial equation. The graphic system renders a polygon with the surface structure using the equation.