Method for implementing the power function DP and computer graph

Details Method for implementing the power function DP and computer graph Method for implementing the power function DP and computer graph

1997-06-16

1999-11-23

Nguyen, Phu K.

Computer graphics processing and selective visual display system

Computer graphics processing

G06T 1700

Patent

active

059908947

ABSTRACT:
A graphics accelerator using an improved method for evaluating a power function. As part of determining realistic shading for objects in a three-dimensional scene, the Phong technique requires repeated evaluation of the power function D.sup.P, where D is a base value and P is a power value with a fractional component. In one embodiment, a hardware implementation of this function determines the logarithm log.sub.2 (D.sup.P) using a table lookup and a multiplication. An anti-logarithm function is then performed as follows. The logarithm log.sub.2 (D.sup.P) is split into three parts: an integer portion I, a five bit fractional portion F, and a remainder fractional portion R. The desired value D.sup.P is then expressible as 2.sup.I 2.sup.F 2.sup.R. The factor 2.sup.F In2 is found using a 32-entry lookup table. The factor 2.sup.R /In2 is closely approximated by adding 1/In2 to R. Multiplying these two factors and shifting by I bits advantageously produces the desired value D.sup.P.

REFERENCES:
patent: 5793371 (1998-08-01), Deering
patent: 5847715 (1998-12-01), Fujita et al.
patent: 5850489 (1998-12-01), Rich
patent: 5850535 (1998-12-01), Maystrovsky et al.
Foley, et al, "Computer Graphics: Principles and Practice," Chapter 16: Illumination and Shading, published by Addison-Wesley Publishing Company, Inc., pp. 721-814 (excluding color plates).

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