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lit.3Cg

NAME

lit - computes lighting coefficients for ambient, diffuse, and specular lighting contributions

SYNOPSIS

   float4 lit(float NdotL, float NdotH, float m);
 
 
 

   half4 lit(half NdotL, half NdotH, half m);
 
 
 

   fixed4 lit(fixed NdotL, fixed NdotH, fixed m);
 
 
 

PARAMETERS

NdotL

The dot product of a normalized surface normal and a normalized light vector.

NdotH

The dot product of a normalized surface normal and a normalized half-angle vector (for Blinn-style specular) where the half-angle vector is the sum of the normalized view vector and normalized light vector. Alternatively, the dot product of a normlized light vector and a normalized view vector reflected by a normalized surface normal could be used (for Phong-style specular).

m

A specular exponent, typically described as a measure of shininess. The larger the exponent, the shinier the specular highlight, the smaller the exponent, the duller the specular highlight.

DESCRIPTION

The lit function is a helper function useful to compute lighting coefficients for ambient, diffuse, and specular lighting contributions. The function efficiently maps to a native instruction for most GPUs.

lit returns a 4-component vector arranged as follows:

x

The ambient coefficient that is always 1.0.

y

The diffuse coefficient that is zero if NdotL is less than zero, and NdotL otherwise.

z

The specular coefficient that is zero if either NdotL or NdotH are less than zero, and otherwise NdotH raised to the power m.

w

Always 1.0.

REFERENCE IMPLEMENTATION

lit accepting <float> parameters could be implemented this way:

   float4 lit(float NdotL, float NdotH, float m)
   {
     float specular = (NdotL > 0) ? pow(max(0.0, NdotH), m);
     return float4(1.0, max(0.0, NdotL), specular, 1.0);
   }
 
 
 

PROFILE SUPPORT

lit is supported in all profiles.

SEE ALSO

dot, max, normalize, pow