lit

> # 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 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