Abstract: A primitive of a base mesh having at least three base vertices is dynamically tessellated to enable smooth changes in detail of an image rendered on a screen. A respective floating point vertex tessellation value (Fv) is assigned to each base vertex of the base mesh, based on a desired level of detail in the rendered image. For each edge of the primitive: a respective floating point edge tessellation rate (Fe) of the edge is calculated using the respective vertex tessellation values (Fv) of the base vertices terminating the edge. A position of at least one child vertex of the primitive is then calculated using the respective calculated edge tessellation rate (Fe). By this means, child vertices of the primitive can be generated coincident with a parent vertex, and smoothly migrate in response to changing vertex tessellation values of the base vertices of the primitive.