5.5.2.6 Primitives with Adjacency
A triangle list with adjacency is where, for each triangle, you also include its three neighboring triangles called adjacent triangles; see Figure 5.14b to observe how these triangles are defined. This is used for the geometry shader, where certain geometry shading algorithms need access to the adjacent triangles. In order for the geometry shader to get those adjacent triangles, the adjacent triangles need to be submitted to the pipeline in the vertex/index buffers along with the triangle itself, and the D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST_ADJ topology must be specified so that the pipeline knows how construct the triangle and its adjacent triangles from the vertex buffer. Note that the vertices of adjacent primitives are only used as input into the geometry shader—they are not drawn. If there is no geometry shader, the adjacent primitives are still not drawn.