The Rendering Pipeline - Practical Rendering and Computation with Direct3D 11 - page 223

Figure 3.69. A sample of using the noperspective interpolation mode.
The nointerpolation mode. As its name implies, the nointerpolation mode does not
perform any interpolation of the vertex attributes. This means that the attribute value of the
first vertex of each primitive will be passed to all fragments for a given primitive, which
produces a constant value over the entire surface of the primitive. This can be used to give
a model a faceted appearance when this interpolation mode is used to modify lighting
related attributes. In effect, not using interpolation will generally make the faces of the
rendered geometry more noticeable, since the whole purpose of using interpolation is to
hide the fact that the vertex-based geometry is approximating a smooth surface. This may
be minimized when using the tessellation system, but could also be a good way to visualize
how finely tessellated the final geometric results are. Figure 3.70 demonstrates the use of
this interpolation mode.
The centroid mode. The centroid interpolation mode is intended to offer a more ap-
propriate interpolation mode for special cases in MSAA rendering modes. When a pixel is
Figure 3.70. A sample of using the nointerpolation interpolation mode.