OpenGL 4.2 (Compatibility Profile) - April 27, 2012

2.6. BEGIN/END PARADIGM 28
Figure 2.8. Triangle strips with adjacency. The vertices connected with solid lines
belong to the main primitives; the vertices connected by dashed lines are the adjacent
vertices that may be used in a geometry shader.
The 6i + 1st, 6i + 3rd, and 6i + 5th vertices (in that order) determine a triangle
for each i = 0, 1, . . . , n − 1, where there are 6n + k vertices between a Begin and
End pair. k is either 0, 1, 2, 3, 4, or 5; if k is non-zero, the final k vertices are
ignored. For triangle i, the i + 2nd, i + 4th, and i + 6th vertices are considered
adjacent to edges from the i + 1st to the i + 3rd, from the i + 3rd to the i + 5th,
and from the i + 5th to the i + 1st vertices, respectively (see figure 2.7).
Triangle Strips with Adjacency
Triangle strips with adjacency are similar to triangle strips, except that each line
triangle edge has an adjacent vertex that can be accessed by a geometry shader. If a
geometry shader is not active, the adjacent vertices are ignored. They are generated
with mode TRIANGLE_STRIP_ADJACENCY.
OpenGL 4.2 (Compatibility Profile) - April 27, 2012