The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Sep. 06, 1994
Filed:
Dec. 20, 1991
Michael Kelley, San Mateo, CA (US);
Stephanie Winner, Santa Clara, CA (US);
Lee Mighdoll, Palo Alto, CA (US);
Apple Computer, Inc., Cupertino, CA (US);
Abstract
A method and apparatus for approximating a value distributed between two endpoints. The method and apparatus are embodied in a rendering device for calculating pixel shading values for the display of 3-D graphical images. The method approximates a function P(w)=(1-w)A+wB, where w is a provided interpolation weight between 0 and 1, A is a first endpoint value and B is a second endpoint value. The method causes exact evaluation for the cases where P(0)=A and P(1)=B. The method is comprised generally of the steps of: providing an interpolation weight value W comprised of N bit values; assigning a first predetermined pattern of N bits (J) to cause said first extreme parameter value A to be generated and a second predetermined pattern of N bits (K) to cause the second extreme parameter value B to be generated; assigning a third predetermined pattern of N bits (L) as a saturation multiplier, performing a linear interpolation to derive a parameter value for a pixel P, using a function ((J-W)A+WB); and adding a saturation value according to the criteria that if W is less than a saturation threshold, adding the quantity (L.times.A) to the result; or if W is greater than or equal to the saturation threshold, adding the quantity (L.times.B) to the result. The apparatus is comprised of a plurality of multiplexors, carry-save adders and a carry-propagate adder.