The system interpolates the characteristics of a triangle's vertices across the triangle when it renders a face. These are the triangle interpolants:
All of the triangle interpolants are modified by the current shade mode:
| Flat | No interpolation is done. Instead, the color of the first vertex in the triangle is applied across the entire face. |
| Gouraud | Linear interpolation is performed between all three vertices. |
The color and specular interpolants are treated differently, depending on the color model. In the RGB color model, the system uses the red, green, and blue color components in the interpolation. In the monochromatic or "ramp" model, the system uses only the blue component of the vertex color.
The alpha component of a color is treated as a separate interpolant because device drivers can implement transparency in two different ways: by using texture blending or by using stippling.
An application uses the dwShadeCaps member of the D3DPRIMCAPS structure to determine what forms of interpolation the current device driver supports.