Introduction to Vertex Shaders - Introduction to 3D Game Programming with DirectX 9.0 - page 310

when the color is combined with the luminance texture, it appears
shaded.
// File: toon.txt
// Desc: Vertex shader that lights geometry so it appears to be
// drawn in a cartoon style.

//
// Globals
//

extern matrix WorldViewMatrix;
extern matrix WorldViewProjMatrix;

extern vector Color;

extern vector LightDirection;

static vector Black = {0.0f, 0.0f, 0.0f, 0.0f};

//
// Structures
//

struct VS_INPUT
{

vector position : POSITION;
vector normal : NORMAL;

};

struct VS_OUTPUT
{

vector position : POSITION;
float2 uvCoords : TEXCOORD;
vector diffuse : COLOR;

};

//
// Main
//

VS_OUTPUT Main(VS_INPUT input)
{

// zero out each member in output
VS_OUTPUT output = (VS_OUTPUT)0;

// transform vertex position to homogenous clip space
output.position = mul(input.position, WorldViewProjMatrix);

//
// Transform lights and normals to view space. Set w
// components to zero since we're transforming vectors.
// Assume there are no scalings in the world
// matrix as well.
//
LightDirection.w = 0.0f;