Texture blending enables applications to create the appearance of a complex texture on a primitive. This works well for smooth surfaces. For instance, your application can use the texture blending feature of Direct3D to apply a smooth wood grain finish onto a tabletop in a scene.
However, texture blending alone is insufficient to model rough surfaces such as the bark of a tree. Fortunately, the Direct3D enables applications to easily use a technique called bump mapping. A Bump map is a texture that stores depth information. That is, it stores the values indicating the high and low spots on a surface.
Your application applies the bump map to the texture using blending stages. Set the texture blending operation of the blending stage containing the bump map to D3DTOP_BUMPENVMAP or D3DTOP_BUMPENVMAPLUMINANCE. For more information, see D3DTEXTUREOP and Creating Blending Stages.