Triangles with a zero inner tessellation level but with a non-zero edge tessellation level (common for those triangles adjacent to the triangles marked for tessellation) will have a single vertex inserted in the middle and connected to all edge vertices (triangle fan). o / \ / \ o o o / / \ \ / / \ \ / o-----o \ o / \ / \ o / / \ / \ \ / o-----o-----o \ / \ o-------o-------o