Graphical processing system, graphical pipeline and method for implementing subpixel shifting to anti-alias texture

A method for selectably performing multisampling and oversampling to sample shading for geometries of a computer-generated object, said method comprising:

• multisampling a first portion of a scene to determine one shading value per pixel;
• and
• oversampling a second portion of said scene by
• shifting shading sample positions relative to a frame of reference that includes said geometries and coverage sample positions such that there is no relative translation between said geometries and said coverage sample positions, said shading sample positions being shifted to provide multiple shading values per pixel,
• wherein said shading sample positions are shifted to establish translated shading sample positions coinciding with said coverage sample positions to reduce aliasing of non-geometric portions of said computer-generated object;
• and
• wherein said shading sample positions are aligned with said coverage samples to produce symmetrical arrangements of said shading sample positions over groupings of pixels, thereby reducing mismatched values of level of detail (“LOD”) that otherwise would introduce LOD artifacts.

A general purpose graphics processing unit (“GPGPU”) comprising:

• a geometry processor configured to generate a geometry in accordance with application program instructions;
• a rasterizer configured to convert said geometry into data representing coverage of subpixels at coverage sample positions;
• a shader to determine shading for subpixels, said shader including:
• a subpixel centroid sampling unit configured to perform centroid multisampling, said subpixel centroid sampling unit being configured to receive a number of subpixel shifting masks to either establish a subpixel centroid that coincides with a coverage sample position or reposition a default centroid from a pixel center to said coverage sample position, and
• a texture unit configured to determine shading for said geometry using said coverage sample positions;
• and
• a raster operations (“ROP”) unit configured to at least perform alpha-testing against said shading for said geometry;
• wherein said subpixel centroid sampling unit comprises:
• a coverage sample determinator configured to determine a number of covered sample positions that are covered by said geometry and a number of uncovered sample positions that are not covered by said geometry, both covered sample positions and uncovered sample positions sharing a frame of reference with said geometry such that there is no relative shifting among said geometry, said covered sample positions and said uncovered sample positions when anti-aliasing said computer-generated images;
• a shading sample selector configured to select either a covered sample position from said number of covered sample positions or an uncovered sample position from said number of uncovered sample positions;
• and
• a shading sample translator configured to establish said subpixel centroid if said covered sample position is selected or to reposition said default centroid if said uncovered sample position is selected,
• wherein said subpixel centroid and said default centroid form symmetrically-spaced texture sample positions over a number of pixels to reduce level of detail (“LOD”) artifacts.