Apparatus and method for processing graphics primitives

A method of operating an apparatus to process graphics primitives for display, comprising:

• performing, by primitive setup circuitry a primitive setup operation to determine a plurality of functions for an input graphics primitive, including an edge function associated with each edge of the input graphics primitive and a depth function associated with the input graphics primitive;
• performing, by rasterization circuitry, a rasterization operation using the edge function associated with each edge of the input graphics primitive in order to calculate position data for a plurality of graphics fragments to be used to represent the input graphics primitive;
• in a default mode of operation, depth bound clipping circuitry performing a depth bound clipping operation by determining, for each graphics fragment in said plurality of graphics fragments, a depth value for said graphics fragment using the depth function, and determining whether said depth value resides within a valid depth range of a view frustum, the graphics fragment being discarded from further processing if its depth value does not reside within said valid depth range;
• and
• responsive to detection of a predetermined condition, control circuitry modifying the primitive setup operation and the rasterization operation for one or more input graphics primitives in order to incorporate depth bound clipping within the rasterization operation for said one or more input graphics primitives, and disabling the default mode of operation in order to disable the depth bound clipping operation;
• the modifying of the primitive setup operation causing the primitive setup operation to additionally determine at least one depth plane edge function for the input graphics primitive;
• and
• the modifying of the rasterization operation causing the rasterization operation to incorporate said at least one depth plane edge function in said rasterization operation.

An apparatus for processing graphics primitives for display, comprising:

• primitive setup means for determining a plurality of functions for an input graphics primitive, including an edge function associated with each edge of the input graphics primitive and a depth function associated with the input graphics primitive;
• rasterization means for performing a rasterization operation using the edge function associated with each edge of the input graphics primitive in order to calculate position data for a plurality of graphics fragments to be used to represent the input graphics primitive;
• depth bound clipping means for performing, in a default mode of operation, a depth bound clipping operation by determining, for each graphics fragment in said plurality of graphics fragments, a depth value for said graphics fragment using the depth function, and determining whether said depth value resides within a valid depth range of a view frustum, the graphics fragment being discarded from further processing if its depth value does not reside within said valid depth range;
• and
• control means for modifying, in response to detection of a predetermined condition, the operation of the primitive setup means and the rasterization means for one or more input graphics primitives in order to incorporate depth bound clipping within the rasterization operation performed by the rasterization means for said one or more input graphics primitives, the control means further for disabling, on detection of said predetermined condition, the default mode of operation in order to disable the depth bound clipping means from performing said depth bound clipping operation;
• wherein:
• the control means modifies the operation of the primitive setup means by causing the primitive setup means to additionally determine at least one depth plane edge function for the input graphics primitive;
• and
• the control means modifies the operation of the rasterization means by causing the rasterization means to incorporate said at least one depth plane edge function in said rasterization operation.