Hierarchical graphics processing for primitives

A method of depth and/or stencil testing when generating a render output in a graphics processing system in which, for the purposes of generating the render output, the render output is divided into a plurality of larger patches, each larger patch encompassing a set of plural smaller patches of the render output, the method comprising:

• performing, by a patch depth and/or stencil testing stage of the graphics processing system subsequent to a rasterization stage of the graphics processing system, the steps of:
• receiving a larger patch in respect of a primitive, wherein no graphics fragments were generated for the larger patch in respect of the primitive in the rasterization stage;
• and
• performing one or more depth and/or stencil tests for the larger patch in respect of the primitive.

A graphics processing system in which, for the purposes of generating a render output, the render output is divided into a plurality of larger patches, each larger patch encompassing a set of plural smaller patches of the render output, the graphics processing system comprising a rasterisation circuit configured to:

• test a larger patch of the render output against a primitive to be processed to determine if the primitive to be processed at least partially covers the larger patch of the render output;
• and
• when it is determined that the primitive only partially covers the larger patch of the render output, sub-divide the larger patch into a set of plural smaller patches of the render output and test at least one of the smaller patches of the render output against the primitive to be processed to determine if the primitive to be processed at least partially covers the at least one smaller patch of the render output;
• and
• when it is determined that the primitive completely covers the larger patch of the render output, output the larger patch in respect of the primitive from the rasterisation circuit for processing by a subsequent stage of the graphics processing system without the rasterisation circuit generating a set of graphics fragments for the larger patch in respect of the primitive;
• and
• the graphics processing system further comprises a subsequent processing circuit configured to, when it is determined that the primitive completely covers the larger patch of the render output, process the larger patch output by the rasterisation circuit in respect of the primitive without the rasterisation circuit generating a set of graphics fragments for the larger patch in respect of the primitive.

A non-transitory computer readable storage medium storing software code which when executing on a processor performs a method of processing a primitive when generating a render output in a graphics processing system in which, for the purposes of generating the render output, the render output is divided into a plurality of larger patches, each larger patch encompassing a set of plural smaller patches of the render output, the method comprising:

• performing, by a rasteriser of the graphics processing system, the steps of:
• testing a larger patch of the render output against a primitive to be processed to determine if the primitive to be processed at least partially covers the larger patch of the render output;
• when it is determined that the primitive only partially covers the larger patch of the render output, sub-dividing the larger patch into a set of plural smaller patches of the render output and testing at least one of the smaller patches of the render output against the primitive to be processed to determine if the primitive to be processed at least partially covers the at least one smaller patch of the render output;
• and
• when it is determined that the primitive completely covers the larger patch of the render output, outputting the larger patch in respect of the primitive from the rasteriser for processing by a subsequent stage of the graphics processing system without the rasteriser generating a set of graphics fragments for the larger patch in respect of the primitive;
• the method further comprising:
• when it is determined that the primitive completely covers the larger patch of the render output, processing by a subsequent stage of the graphics processing system, the larger patch output by the rasteriser in respect of the primitive without the rasteriser generating a set of graphics fragments for the larger patch in respect of the primitive.