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

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.

What is claimed is:  
     
         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: 
       Blended Color=α·First Color+(1−α)·Second Color, 
       where α is the coverage area.  
     
     
         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.    
     
     
         9 . Frame buffer circuitry within a computer graphics system for rendering an anti-aliased graphics scene comprising: 
 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.    
     
     
         10 . The frame buffer circuitry of  claim 9 , wherein each of the memory segments maps to a two dimensional array of pixels.  
     
     
         11 . The frame buffer circuitry of  claim 9 , wherein the blending information includes a coverage value, wherein the coverage value is an approximation of an area of a pixel interior to a primitive edge.  
     
     
         12 . The frame buffer circuitry of  claim 11 , wherein the coverage area is one for pixels that are wholly interior to a primitive, and are not blended with adjacent pixels.  
     
     
         13 . The frame buffer circuitry of  claim 11 , wherein the coverage area is stored in five bits of information.  
     
     
         14 . The frame buffer circuitry of  claim 9 , wherein the blending information further includes direction information.  
     
     
         15 . The frame buffer circuitry of  claim 14 , wherein the direction information includes an identification of a direction to a pixel adjacent a current pixel, and which borders an external primitive edge.  
     
     
         16 . The frame buffer circuitry of  claim 15 , wherein the direction information is encoded into three bits.