Method for generating addresses to textured graphics primitives stored in rip maps

• US 5,222,205 A
• Filed: 03/16/1990
• Issued: 06/22/1993
• Est. Priority Date: 03/16/1990
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Company (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Larson, Ronald D., Shah, Monish S.
• Primary Examiner(s): Harkcom, Gary V.
• Assistant Examiner(s): Ba, Huynh
• Application Number:
  US07/494,706
• Time in Patent Office: 1,194 Days
• Field of Search: 395/130, 395/131, 395/126
• US Class Current: 345/587
• CPC Class Codes: G06T 15/04 Texture mapping

Abstract

Methods for texture mapping graphics primitives in a graphics pipeline architecture system. The methods utilize rectangular box filters to down-sample original texture maps thereby optimizing aliasing and blurring when graphics primitives have a two-dimensional texture mapped to a three-dimensional object. The methods of texture mapping graphics primitives in a frame buffer graphics system comprise the steps of determining an original texture map of two dimensions for a surface, storing the original texture map in the frame buffer, sampling the original texture map independently using an asymmetrical filter to construct multiple versions of a texture and to address textured pixels on a display in the frame buffer graphics systems, mapping the textured pixels to areas on the frame buffer, and displaying the textured graphics primitives on the display. A technique for addressing textured pixels stored in a rectangular texture (RIP) map is also described.

Claims

1. A method of addressing a rectangular texture map stored in a frame buffer and displaying a textured graphics primitive on a display device, comprising the steps of:

obtaining texture coordinate values S and T at the center of a pixel in screen space of said display device;

calculating texture gradient values log₂ Δ

S and log₂ Δ

T as an approximation of an area in texture space covered by said pixel;

calculating an S address to said frame buffer for said S texture coordinate value by;

(a) truncating said S texture coordinate value to the size of a predetermined texture,

(b) choosing one of a texture map for said predetermined texture and a down-sampled rectangular texture map corresponding to said predetermined texture for display on said display device,

(c) using log₂ Δ

S, shifting predetermined logical values into said S texture coordinate value starting at an upper bit one greater than a most significant bit of said S texture coordinate value after truncation in said S address calculating step so as to obtain a modified value for said S texture coordinate value, and

(d) adding said modified value for said S texture coordinate value to a coordinate origin value for said S and T coordinate values as an offset into said rectangular texture map so as to form said S address to said frame buffer;

calculating a T address to said frame buffer for said T texture coordinate value by repeating said steps (a) through (d) using said T texture coordinate value in place of said S texture coordinate value and using log₂ Δ

T in place of log₂ Δ

S; and

displaying a textured graphics primitive on said display device corresponding to a rectangular texture map stored in said frame buffer at said S and T addresses of said frame buffer.

2. A method as in claim 1, wherein textured data read from said frame buffer at said S and T addresses is combined with light source color data and written back to said frame buffer prior to display on said display device.

3. A method as in claim 2, wherein said light source color data is perspective interpolated for each pixel and combined with said textured data to obtain diffuse and specular components for said textured graphics primitive for display on said display device.