Hidden surface removal in graphics processing systems

A graphics processing system, comprising:

• a graphics processing pipeline comprising:
• a rasteriser that rasterises input primitives to generate graphics fragments, each graphics fragment having one or more sampling points associated with it;
• a renderer that processes fragments generated by the rasteriser to generate output fragment data;
• an early culling tester configured to perform an early culling test on fragments generated by the rasteriser before the fragments are sent to the renderer for processing;
• a late culling tester configured to perform a late culling test on fragments that have been processed by the renderer before the fragments are output by the renderer to provide output fragment data for sampling points associated with the fragments;
• and
• a culling test data buffer configured to store data values for use by the early and late culling testers;
• the graphics processing system further comprising:
• state information providing processing circuitry configured to provide for a graphics fragment generated by the rasteriser:
• a first set of state information indicative of whether to perform an early culling test or a late culling test operation to determine whether to cull the fragment;
• and
• a second, separate, set of state information indicative of whether to update the culling test data buffer with data for the fragment based on an early culling test or a late culling test operation;
• and
• the graphics processing pipeline further being configured to:
• subject a fragment to an early culling test or a late culling test operation in accordance with a first set of state information provided for the fragment to determine whether to cull the fragment or not;
• and
• determine whether to update the culling test data buffer with data for a fragment based on an early culling test or a late culling test operation in accordance with a second set of state information provided for the fragment.

A non-transitory computer readable storage medium storing computer software code which when executing on at least one processor performs a method of setting state information for graphics fragments to be processed by a graphics processing pipeline, the method comprising:

• for at least one graphics fragment to be processed:
• determining from requests received for graphics processing operations from an application that requires graphics processing by the graphics processing pipeline:
• whether to perform an early culling test or a late culling test operation to determine whether to cull the at least one graphics fragment;
• and
• whether to update a culling test data buffer using data for the at least one graphics fragment based on an early culling test or a late culling test operation;
• and
• providing for the at least one graphics fragment:
• a first set of state information indicative of whether to perform an early culling test or a late culling test operation selected to determine whether to cull the at least one fragment;
• and
• a second, separate, set of state information indicative of whether to update the culling test data buffer with data for the fragment based on an early culling test or a late culling test operation.