Tessellation method using vertex tessellation factors

A hardware tessellation unit comprising hardware logic configured to:

• a) receive an input comprising four vertices defining a quad patch, each vertex comprising a domain space coordinate and a vertex tessellation factor;
• b) divide the patch into two or four triangles;
• and
• c) in response to determining that at least one tessellation factor exceeds a threshold value:
• generate a center vertex to the patch,
• define a vertex to be a selected vertex,
• add two new vertices to sub-divide each edge between the selected vertex and a neighbor vertex,
• provide the four vertices, which define a sub-quad and comprise the defined vertex, the center vertex and the two new vertices as a further input to (a), and
• add a new vertex to sub-divide an edge between the selected vertex and the neighbor vertex with the vertex tessellation factor which exceeds the threshold and divide a sub-quad defined by the defined vertex, the newly added vertex, the center vertex and the other neighbor vertex into two triangles by connecting the defined vertex to a diagonally opposite vertex in the sub-quad.

A non-transitory computer-readable storage medium having stored thereon computer readable instructions that, when executed by a computer, cause the computer to perform a method of tessellation in a computer graphics system, the method comprising:

• a) receiving an input comprising four vertices defining a quad patch, each vertex comprising a domain space coordinate and a vertex tessellation factor;
• b) dividing the patch into two or four triangles;
• and
• c) in response to determining that at least one tessellation factor exceeds the threshold value:
• generating a center vertex to the patch,
• defining a vertex to be a selected vertex,
• adding two new vertices to sub-divide each edge between the selected vertex and a neighbor vertex,
• providing the four vertices, which define a sub-quad and comprise the defined vertex, the center vertex and the two new vertices as a further input to (a), and
• adding a new vertex to sub-divide an edge between the selected vertex and the neighbor vertex with the vertex tessellation factor which exceeds the threshold and divide a sub-quad defined by the defined vertex, the newly added vertex, the center vertex and the other neighbor vertex into two triangles by connecting the defined vertex to a diagonally opposite vertex in the sub-quad.