gl_TessLevelOuter[] = 1, gl_TessLevelInner[] = 1.
gl_TessLevelOuter[] = 6, gl_TessLevelInner[] = 6.
gl_TessLevelOuter[] = 12, gl_TessLevelInner[] = 12.
gl_TessLevelOuter[] = 36, gl_TessLevelInner[] = 36.
In my last post about OpenGL 4 tessellation I didn't use vertex points as patch control points so there was no change in the geometry. This time I produced a Bézier patch of 16 control points using 2D Gaussian distribution. The result is much funny this time. I checked OpenGL 4 reference page and haven't found anything about tessellation level limitation.
For produce surface from control points, lecture 8 of http://graphics.ucsd.edu/courses/cse167_w06/ will be
a good reference. I also used this course as reference when I was a Computer Graphics TA for senior students.