Compression and Decompression of Sub-Primitive Presence Indications for Use in a Rendering System

A non-transitory computer readable storage medium having stored thereon an integrated circuit definition dataset that, when processed in an integrated circuit manufacturing system, configures the integrated circuit manufacturing system to manufacture a decompression unit configured to decompress compressed data to determine sub-primitive presence indications for use in intersection testing in a rendering system, the decompression unit being configured to:

• determine whether child-level data is included in a hierarchical representation a parent region in a block of compressed data for a block of sub-primitive presence indications, wherein the block of sub-primitive presence indications is subdivided into a plurality of parent regions, each of the parent regions being subdivided into a plurality of child regions, wherein the block of compressed data comprises the hierarchical representation of the block of sub-primitive presence indications, wherein for each of one or more parent regions whose child regions all have the same presence state, parent-level data is included in the hierarchical representation to represent the presence state of the parent region without child-level data for the child regions within the parent region being included in the hierarchical representation;
• and
• in response to determining that child-level data is not included in the hierarchical representation for said parent region, use parent-level data for said parent region, without child-level data, to determine one or more sub-primitive presence indications in said parent region.