OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Shared Tessellated Edges and Cracking

Often a geometric model that uses tessellation will have patches with shared edges. Tessellation in OpenGL guarantees that the geometry generated for the primitives within a patch won’t have any cracks between them, but it can’t make the same claim for patches that share edges. That’s something the application needs to address, and clearly the starting point is that shared edges need to be tessellated the same amounts. However, there’s a secondary issue that can creep in—precision in mathematical computations done by a computer.

For all but trivial tessellation applications, the points along a perimeter edge will be positioned using multiple tessellation control shader output-patch vertices, which are combined ...