Deferred shading graphics processing unit, geometry data structure and method of performing anti-aliasing in deferred shading

1. A graphics processing subsystem operable to render a scene having a pixel represented by samples, comprising:

a memory configured to store a geometry data structure associated with said pixel containing surface fragment coverage masks associated with said samples; and

a graphics processing unit (GPU) configured to employ said surface fragment coverage masks to form a coverage matrix and carry out deferred shading on said pixel, wherein said GPU is further configured to rectify said coverage matrix such that said coverage matrix is symmetric before carrying out said deferred shading.

2. The graphics processing subsystem recited in claim 1 wherein said symmetric coverage matrix is a raster coverage matrix.

3. The graphics processing subsystem recited in claim 2 wherein said GPU is further configured to carry-out a bit-wise logical AND operation on said raster coverage matrix and a transpose of said raster coverage matrix.

4. The graphics processing subsystem recited in claim 1 wherein said surface fragment coverage masks form a post-Z coverage matrix.

5. The graphics processing subsystem recited in claim 1 wherein said geometry data structure further contains a normal vector associated with said pixel.

6. The graphics processing subsystem recited in claim 1 wherein said GPU is further configured to employ said surface fragment coverage masks to determine a number of unique surface fragments covered by said pixel and map said number of unique surface fragments to said samples.

7. A method of shading a pixel represented by samples in a previously rendered scene, comprising:

employing surface fragment coverage masks associated with said samples in determining a number of unique surface fragments covering said pixel;

employing said surface fragment coverage masks in generating a mapping of said unique surface fragments to said samples; and

carrying out, using a streaming multiprocessor in a graphics processing unit, deferred shading on said pixel according to said number of unique surface fragments and said mapping;

wherein a coverage matrix is formed from said surface fragment coverage masks and is rectified such that said coverage matrix is symmetric before carrying out said determining and said generating.

8. The method recited in claim 7 wherein said coverage matrix includes a raster coverage matrix.

9. The method recited in claim 8 wherein said coverage matrix is rectified by carrying out a bit-wise logical AND operation on said raster coverage matrix and a transpose of said raster coverage matrix.

10. The method recited in claim 7 wherein said surface fragment coverage masks includes a post-Z coverage matrix.

11. The method recited in claim 7 wherein said deferred shading comprises shading said pixel once for each of said unique surface fragments.

12. The method recited in claim 7 wherein each of said unique surface fragments covers a unique subset of said samples, said subset being unique with respect to all other subsets covered by each other of said unique surface fragments.

13. A graphics processing unit (GPU) operable to render a scene containing a pixel, comprising:

a rasterizer configured to generate surface attributes associated with visible geometry within said pixel and surface fragment coverage masks associated with samples of said pixel;

a memory configured to store a geometry data structure associated with said pixel containing:

said surface attributes, and

said surface fragment coverage masks; and

a shader configured to employ said geometry data structure in carrying out deferred shading on said pixel;

wherein said GPU is configured to employ said surface fragment coverage masks to form a coverage matrix and said GPU is further configured to rectify said coverage matrix such that said coverage matrix is symmetric before carrying out said deferred shading.

14. The GPU recited in claim 13 wherein said shader is further configured to employ said surface fragment coverage masks to determine a number of unique surface fragments covering said pixel and map said unique surface fragments to said samples.

15. The GPU recited in claim 13 wherein said symmetric coverage matrix is a raster coverage matrix.

16. The GPU recited in claim 15 wherein said GPU is further configured to carry out a bit-wise logical AND operation on said raster coverage matrix and a transpose of said raster coverage matrix.

17. The GPU recited in claim 13 wherein said surface fragment coverage masks form a post-Z coverage matrix.

18. The GPU recited in claim 13 wherein said surface attributes include albedo data associated with said pixel.