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.rm #[ #] #H #V #F C
.IX Title "refract Cg"
.TH refract Cg "" "Cg Toolkit 1.5" "Cg Standard Library"
.UC
.SH "NAME"
\&\fBrefract\fR \- computes a refraction vector.
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 3
\&  fixed3 refract( fixed3 i, fixed3 n, fixed eta );
\&  half3  refract( half3  i, half3  n, half  eta );
\&  float3 refract( float3 i, float3 n, float eta );
.Ve
.SH "PARAMETERS"
.IX Header "PARAMETERS"
.Ip "i" 8
.IX Item "i"
Incidence vector.
.Ip "n" 8
.IX Item "n"
Normal vector.
.Ip "eta" 8
.IX Item "eta"
Ratio of indices of refraction at the surface interface.
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Returns a refraction vector given an incidence vector, a normal vector for
a surface, and a ratio of indices of refraction at the surface's interface.
.PP
The incidence vector \fIi\fR and normal vector \fIn\fR should be normalized.
.SH "REFERENCE IMPLEMENTATION"
.IX Header "REFERENCE IMPLEMENTATION"
\&\fBreflect\fR for \fBfloat3\fR vectors could be implemented this way:
.PP
.Vb 7
\&  float3 refract( float3 i, float3 n, float eta )
\&  {
\&    float cosi = dot(-i, n);
\&    float cost2 = 1.0f - eta * eta * (1.0f - cosi*cosi);
\&    float3 t = eta*i + ((eta*cosi - sqrt(abs(cost2))) * n);
\&    return t * (float3)(cost2 > 0);
\&  }
.Ve
.SH "PROFILE SUPPORT"
.IX Header "PROFILE SUPPORT"
\&\fBrefract\fR is supported in all profiles.
.PP
Support in the fp20 is limited.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
the abs manpage,
the cos manpage,
the dot manpage,
the reflect manpage,
the sqrt manpage
