Rasterisation in graphics processing systems

A graphics processing pipeline comprising:

• a plurality of processing stages, including a rasteriser that rasterises input primitives to generate graphics fragments to be processed, each graphics fragment is associated with one or more sampling points, and a renderer that processes fragments generated by the rasteriser to generate output fragment data;
• and wherein the rasteriser is configured to, upon receiving a primitive to be rasterised, for each of one or more first-level patches representing respective different regions of a render output to be generated:
• test the respective first-level patch against edges of the primitive to determine if the primitive at least partially covers any second-level patch of a set of plural second-level patches of the render output that the respective first-level patch of the render output encompasses, wherein each second-level patch of the set of plural second-level patches is smaller than the respective first-level patch;
• and if the primitive does at least partially cover any second-level patch of the set of plural second-level patches of the render output that the respective first-level patch of the render output encompasses, subdivide the respective first-level patch of the render output into the set of plural second-level patches that the respective first-level patch of the render output encompasses, and for each second-level patch of the render output that the primitive does at least partially cover:
• test the respective second-level patch of the render output against edges of the primitive to determine if the primitive at least partially covers any third-level patch of a set of plural third-level patches of the render output that the respective second-level patch of the render output encompasses, wherein each third-level patch of the set of plural third-level patches is smaller than the respective second-level patch;
• and wherein the rasteriser is further configured to:
• generate one or more graphics fragments for rendering for patches of the render output found to be covered at least in part by the primitive, each graphics fragment is associated with one or more sampling points of the render output;
• and
• issue graphics fragments to the renderer for processing;
• and wherein the rasteriser is further configured to:
• if a smaller patch of the render output in a set of smaller patches of the render output encompassed by a larger patch of the render output that the larger patch of the render output is to be subdivided into is found when the larger patch of the render output is tested to entirely pass an edge test for an edge of the primitive, note in state information associated with the edge of the primitive that the smaller patch of the render output has been found to entirely pass the edge test for the edge of the primitive, and use that state information when testing the smaller patch of the render output that was found when tested to entirely pass the edge test for the edge of the primitive against the primitive to skip the edge test of the edge of the primitive against the smaller patch of the render output.

A non-transitory computer readable storage medium storing computer software code which when executing on a processor performs a method of performing rasterisation in a graphics processing pipeline that includes a plurality of processing stages including a rasteriser that rasterises input primitives to generate graphics fragments to be processed, each graphics fragment is associated with one or more sampling points, and a renderer that processes fragments generated by the rasteriser to generate output fragment data, the method comprising:

• the rasteriser, upon receiving a primitive to be rasterised, for each of one or more first-level patches representing respective different regions of a render output to be generated:
• testing the respective first-level patch against edges of the primitive to determine if the primitive at least partially covers any second-level patch of a set of plural second-level patches of the render output that the respective first-level patch of the render output encompasses, wherein each second-level patch of the set of plural second-level patches is smaller than the respective first-level patch;
• and if the primitive does at least partially cover any second-level patch of the set of plural second-level patches of the render output that the respective first-level patch of the render output encompasses, subdividing the respective first-level patch of the render output into the set of plural second-level patches that the respective first-level patch of the render output encompasses, and for each second-level patch of the render output that the primitive does at least partially cover:
• testing the respective second-level patch of the render output against edges of the primitive to determine if the primitive at least partially covers any third-level patch of a set of plural third-level patches of the render output that the respective second-level patch of the render output encompasses, wherein each third-level patch of the set of plural third-level patches is smaller than the respective second-level patch;
• the method further comprising the rasteriser:
• generating one or more graphics fragments for rendering for patches of the render output found to be covered at least in part by the primitive, each graphics fragment is associated with one or more sampling points of the render output;
• and
• issuing the graphics fragments to the renderer for processing;
• and the method further comprising:
• if a smaller patch of the render output in a set of smaller patches of the render output encompassed by a larger patch of the render output that the larger patch of the render output is to be subdivided into is found when the larger patch of the render output is tested to entirely pass an edge test for an edge of the primitive, noting in state information associated with the edge of the primitive that the smaller patch of the render output has been found to entirely pass the edge test for the edge of the primitive, and using that state information when testing the smaller patch of the render output that was found when tested to entirely pass the edge test for the edge of the primitive against the primitive to skip the edge test of the edge of the primitive against the smaller patch of the render output.