System and method for reducing the effects of aliasing in a computer graphics system

• US 6,429,877 B1
• Filed: 07/30/1999
• Issued: 08/06/2002
• Est. Priority Date: 07/30/1999
• Status: Expired due to Term

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Stroyan, Howard D
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): LESPERANCE, JEAN E
• Application Number:
  US09/365,115
• Time in Patent Office: 1,103 Days
• Field of Search: 345/136, 345/592, 345/431, 345/611, 345/612, 345/614, 345/589, 345/613, 345/469.1, 345/470, 395/131
• US Class Current: 345/611
• CPC Class Codes: G06T 15/503 Blending, e.g. for anti-aliasing
• CPC Class Codes: G06T 2200/12 involving antialiasing
• CPC Class Codes: G09G 2340/10 Mixing of images, i.e. displayed pixel being the result of an operation, e.g. adding, on the corresponding input pixels
• CPC Class Codes: G09G 5/20 Function-generator circuits, e.g. circle generators line or curve smoothing circuits
• CPC Class Codes: G09G 5/39 Control of the bit-mapped memory

Abstract

The present invention is generally directed to a system and method for anti-aliasing edges of adjacent primitives. In accordance with one aspect of the invention, a method operates by determining whether a pixel is an edge pixel of a filled primitive, approximating a coverage area of the pixel, the coverage area being the area of the pixel interior to the primitive edge, determining a direction from the pixel center to an external edge of the primitive, and blending a first color of the primitive with a second color, the second color being a color of a pixel of a second primitive adjacent the external edge. In accordance with another aspect of the invention, a system is provided having frame buffer circuitry uniquely configured for rendering an anti-aliased graphics scene. In accordance with one embodiment, the frame buffer circuitry includes a first memory segment for storing color values associated with pixels, a second memory segment for storing alpha values associated with the pixels, a third memory segment for storing depth values associated with the pixels, and a fourth memory segment for storing anti-alias blending information associated with the pixels.

Claims

1. An anti-aliasing method comprising the steps of:

determining whether a pixel is an edge pixel of a filled primitive;

approximating a coverage area of the pixel, the coverage area being the area of the pixel interior to the primitive edge;

determining a direction from the pixel center to an external edge of the primitive; and

blending a first color of the primitive with a second color, the second color being a color of a pixel of a second primitive adjacent the external edge.

2. The method of claim 1, wherein the step of determining a direction from the pixel center includes determining whether the external edge is in a direction selected from the group consisting of:

left of the pixel center, right of the pixel center, above the pixel center; and

below the pixel center.

3. The method of claim 2, further including the step of encoding the direction from the pixel center to the external edge.

4. The method of claim 3, further including the step of storing the encoded direction and associating a storage location of the encoded value with the pixel.

5. The method of claim 1, wherein the step of blending a first color with a second color is performed after an entire graphic scene has been rasterized.

6. The method of claim 1, wherein the step of blending a first color with a second color more specifically includes blending the first color with a color of a second pixel, the second pixel being adjacent the pixel and in the direction.

7. The method of claim 1, wherein the step of blending a first color with a second color blends the first and second color in accordance with the following equation:

8. An anti-aliasing method comprising the steps of:

evaluating a pixel to determine whether the pixel is on the edge of a filled primitive;

determining a coverage area of the pixel;

determining a direction from the pixel center to an external edge of the primitive; and

blending a first color of the primitive with a second color, the second color being a color of a second primitive adjacent the pixel and in the determined direction.