Assigning primitives to tiles in a graphics processing system

A tiling unit configured to assign primitives to tiles in a graphics processing system which has a rendering space subdivided into a plurality of tiles, wherein each tile comprises one or more polygonal regions for which depth comparisons are to be performed, the tiling unit being configured to receive a plurality of primitives forming a mesh, wherein the tiling unit comprises:

• mesh logic configured to:
• identify external edges of the mesh,
• identify intersection points where the identified external edges of the mesh intersect with lines aligned with the edges of a polygonal region of a tile, and
• use the identified intersection points to determine whether the mesh entirely covers the polygonal region of the tile;
• tiling logic configured to, for each of a plurality of the received primitives which are present within the polygonal region of the tile:
• compare a first depth value for that primitive with a depth threshold for the polygonal region, and
• in dependence on the result of the comparison, selectively include an indication of the primitive in a display list for the tile to thereby assign the primitive to the tile;
• and
• depth threshold updating logic configured to, if it is determined that the mesh entirely covers the polygonal region of the tile, update the depth threshold for the polygonal region in dependence on a comparison of the depth threshold for the polygonal region with a second depth value for at least one of said plurality of the received primitives of the mesh which is present within the polygonal region of the tile.

A non-transitory computer readable storage medium having stored thereon processor executable instructions that when executed cause at least one processor to assign primitives to tiles in a graphics processing system which has a rendering space subdivided into a plurality of tiles, wherein each tile comprises one or more polygonal regions for which depth comparisons are to be performed, the assigning of primitives to tiles comprising:

• receiving a plurality of primitives forming a mesh;
• identifying external edges of the mesh;
• identifying intersection points where the identified external edges of the mesh intersect with lines aligned with the edges of a polygonal region of a tile, and using the identified intersection points to determine whether the mesh entirely covers the polygonal region of the tile;
• and
• for each of a plurality of the received primitives which are present within the polygonal region of the tile:
• (i) comparing a first depth value for the primitive with a depth threshold for the region;
• and
• (ii) in dependence on the result of the comparison, selectively including an indication of the primitive in a display list for the tile to thereby assign the primitive to the tile;
• and
• if it is determined that the mesh entirely covers the polygonal region of the tile, updating the depth threshold for the polygonal region in dependence on a comparison of the depth threshold for the polygonal region with a second depth value for at least one of said plurality of the received primitives of the mesh which is present within the polygonal region of the tile.

A non-transitory computer readable storage medium having stored thereon computer readable instructions that, when processed at a computer system for generating a manifestation of an integrated circuit, cause the computer system to generate a manifestation of a tiling unit configured to assign primitives to tiles in a graphics processing system which has a rendering space subdivided into a plurality of tiles, wherein each tile comprises one or more polygonal regions for which depth comparisons are to be performed, the tiling unit being configured to receive a plurality of primitives forming a mesh, wherein the tiling unit comprises:

• mesh logic configured to:
• identify external edges of the mesh,
• identify intersection points where the identified external edges of the mesh intersect with lines aligned with the edges of a polygonal region of a tile, and
• use the identified intersection points to determine whether the mesh entirely covers the polygonal region of the tile;
• tiling logic configured to, for each of a plurality of the received primitives which are present within the polygonal region of the tile:
• compare a first depth value for the primitive with a depth threshold for the region;
• and
• in dependence on the result of the comparison, selectively include an indication of the primitive in a display list for the tile to thereby assign the primitive to the tile;
• and
• depth threshold updating logic configured to, if it is determined that the mesh entirely covers the polygonal region of the tile, update the depth threshold for the polygonal region in dependence on a comparison of the depth threshold for the polygonal region with a second depth value for at least one of said plurality of the received primitives of the mesh which is present within the polygonal region of the tile.