source: downloads/Samples/Media/materials/programs/Example_CelShading.cg @ 3

/* Cel shading vertex program for single-pass rendering
   In this program, we want to calculate the diffuse and specular
   ramp components, and the edge factor (for doing simple outlining)
   For the outlining to look good, we need a pretty well curved model.
*/
void main_vp(float4 position    : POSITION,
                         float3 normal          : NORMAL,
                         // outputs
                         out float4 oPosition : POSITION,
                         out float  diffuse              : TEXCOORD0,
                         out float  specular     : TEXCOORD1,
                         out float  edge                 : TEXCOORD2,
                         // parameters
                         uniform float3 lightPosition, // object space
                         uniform float3 eyePosition,   // object space
                         uniform float4  shininess,
                         uniform float4x4 worldViewProj)
{
        // calculate output position
        oPosition = mul(worldViewProj, position);

        // calculate light vector
        float3 N = normalize(normal);
        float3 L = normalize(lightPosition - position.xyz);
        
        // Calculate diffuse component
        diffuse = max(dot(N, L) , 0);

        // Calculate specular component
        float3 E = normalize(eyePosition - position.xyz);
        float3 H = normalize(L + E);
        specular = pow(max(dot(N, H), 0), shininess);
        // Mask off specular if diffuse is 0
        if (diffuse == 0) specular = 0;

        // Edge detection, dot eye and normal vectors
        edge = max(dot(N, E), 0);
}

void main_fp(float diffuseIn    : TEXCOORD0,
                         float specularIn       : TEXCOORD1,
                         float edge             : TEXCOORD2,
                         
                         out float4 colour      : COLOR,
                         
                         uniform float4 diffuse,
                         uniform float4 specular,
                         
                         uniform sampler1D diffuseRamp,
                         uniform sampler1D specularRamp,
                         uniform sampler1D edgeRamp)
{
        // Step functions from textures
        diffuseIn = tex1D(diffuseRamp, diffuseIn).x;
        specularIn = tex1D(specularRamp, specularIn).x;
        edge = tex1D(edgeRamp, edge).x;

        colour = edge * ((diffuse * diffuseIn) + 
                                        (specular * specularIn));
}