Tessellation method using recursive sub-division of triangles

A non-transitory computer readable storage medium having stored thereon computer executable program code that when executed causes at least one processor to perform tessellation of surface patches of objects in a 3-D computer graphics scene by,

• for an initial patch comprising a left vertex and a right vertex connected by an edge and defined in domain space:
• comparing a vertex tessellation factor of the left vertex and a vertex tessellation factor of the right vertex to a threshold value;
• in response to determining that neither of the vertex tessellation factors of the left and right vertices exceed the threshold value, outputting data describing the initial patch;
• and
• in response to determining that either of the vertex tessellation factors of the left and right vertices exceed the threshold value, forming a new vertex sub-dividing the edge into two parts, calculating a vertex tessellation factor for the new vertex, dividing the initial patch to form a first new patch comprising the left vertex and the new vertex and a second new patch comprising the right vertex and the new vertex and reducing the vertex tessellation factor of each vertex in each of the newly formed patches;
• and
• using the newly formed patches in rendering a scene in the computer graphics system.

A hardware tessellation unit comprising hardware logic configured to, for an initial patch comprising a left vertex and a right vertex connected by an edge and defined in domain space, said initial patch representing part of a surface in a 3-D computer graphics scene:

• compare a vertex tessellation factor of the left vertex and a vertex tessellation factor of the right vertex to a threshold value;
• in response to determining that neither of the vertex tessellation factors of the left and right vertices exceed the threshold value, output data describing the initial patch;
• and
• in response to determining that either of the vertex tessellation factors of the left and right vertices exceed the threshold value, form a new vertex sub-dividing the edge into two parts, calculate a vertex tessellation factor for the new vertex, divide the initial patch to form a first new patch comprising the left vertex and the new vertex and a second new patch comprising the right vertex and the new vertex and reduce the vertex tessellation factor of each vertex in each of the newly formed patches;
• and
• output the newly formed patches for use in rendering said 3-D computer graphics scene.