Tessellation method using displacement factors

A graphics processing unit comprising:

• a tessellator arranged to receive data defining each corner vertex in one or more input patches, and comprising logic arranged to perform tessellation on the plurality of input patches using the vertex tessellation factors to generate and output a plurality of primitives defined by vertices, the tessellation comprising adding one or more new child vertices, and wherein the tessellator further comprises logic arranged to calculate a displacement factor for each newly added child vertex, wherein a newly added child vertex is added at a position on an edge connecting two existing vertices, the two existing vertices being parent vertices for the child vertex, and wherein the displacement factor for the newly added vertex is calculated based on the vertex tessellation factors of the two parent vertices and/or the child vertex;
• a blend shader arranged, for each child vertex, to modify a received target world space parameter for the child vertex using the displacement factor for the child vertex and world space parameters for the parent vertices by:
• generating a starting state of a world space parameter for the child vertex by interpolating between the world space parameters for the parent vertices;
• and
• interpolating, using the displacement factor for the child vertex, between the starting state of the world space parameter for the child vertex and the target world space parameter for the child vertex;
• and
• a rasterizer arranged to receive the modified target world space parameter and use the modified target world space parameter for rendering an input patch.

A non-transitory computer readable storage medium having stored thereon computer dataset description that, when processed, causes an integrated circuit manufacturing system to generate a graphics pipeline configured to:

• determine a vertex tessellation factor for each corner vertex in one or more input patches;
• perform tessellation on the one or more input patches using the vertex tessellation factors to generate a plurality of primitives defined by vertices, the tessellation comprising adding one or more new child vertices and calculating a displacement factor for each newly added child vertex, wherein a newly added child vertex is added at a position on an edge connecting two existing vertices, the two existing vertices being parent vertices for the child vertex, and wherein the displacement factor for the newly added vertex is calculated based on the vertex tessellation factors of the two parent vertices and/or the child vertex;
• and
• generate a world space parameter for each vertex by calculating a target world space parameter for each vertex and modifying the target world space parameter for a child vertex using the displacement factor for the child vertex and the world space parameters for the parent vertices by:
• generating a starting state of the world space parameter for the child vertex by interpolating between the world space parameters for the parent vertices;
• and
• calculating a modified world space parameter for the child vertex based on the displacement factor for the child vertex, the starting state of the world space parameter for the child vertex and the target world space parameter for the child vertex.