Graphics processing systems

A graphics processing pipeline which processes graphic primitives to generate a render output, each primitive being defined by a set of vertices, the vertices having respective coordinates and the set of vertices of each primitive defining an area of the primitive, wherein the area of each primitive has a sign that is positive or negative, the pipeline comprising:

• testing circuitry configured to:
• determine a difference between coordinates of vertices of a primitive;
• determine a size of the primitive using the determined difference between coordinates of vertices of the primitive;
• and
• determine whether the determined size of the primitive meets a particular size condition;
• facing direction determination circuitry configured to, for a primitive meeting the particular size condition:
• determine the sign of the area of the primitive using the set of vertices of the primitive;
• and
• when the sign of the area of the primitive is determined to be positive, determine that a facing direction of the primitive is a first direction;
• but
• when the sign of the area of the primitive is determined to be negative, determine that the facing direction of the primitive is a second direction different from the first direction;
• facing direction culling circuitry configured to cull from further processing any primitive that the facing direction of is determined to match any of one or more culling facing directions;
• and
• processing circuitry configured to process any primitive that the facing direction of is not determined to match any of the one or more culling facing directions to generate a render output.

A non-transitory computer readable storage medium storing computer software code which when executing on at least one processor performs a method of operating a graphics processing pipeline which processes graphics primitives, the method comprising:

• when the graphics processing pipeline is processing a plurality of graphics primitives to generate a render output, each primitive being defined by a set of vertices, the vertices having respective coordinates, and the set of vertices of each primitive defining an area of the primitive, wherein the area of each primitive has a sign that is positive or negative:
• culling graphics primitives of the plurality of graphics primitives being processed by the graphics processing pipeline, by:
• for each primitive of the plurality of primitives:
• determining a difference between coordinates of vertices of the primitive;
• determining a size of the primitive using the determined difference between coordinates of vertices of the primitive;
• and
• determining whether the determined size of the primitive meets a particular size condition;
• and
• for each primitive meeting the particular size condition:
• determining the sign of the area of the primitive using the set of vertices of the primitive;
• and
• when the sign of the area of the primitive is determined to be positive, determining that a facing direction of the primitive is a first direction;
• but
• when the sign of the area of the primitive is determined to be negative, determining that the facing direction of the primitive is a second direction different from the first direction;
• culling from further processing those primitives that the facing direction of is determined to match any of one or more culling facing directions;
• and
• processing to generate the render output any primitive of the plurality of primitives that the facing direction of is not determined to match any of the one or more culling facing directions.