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<BLOCKQUOTE>
<H1><A NAME="NAME"><A NAME="1">NAME
</A></A></H1>
<P>
<B>faceforward</B> - returns a normal as-is if a vertex's eye-space position
vector points in the opposite direction of a geometric normal, otherwise
return the negated version of the normal
</P>
<H1><A NAME="SYNOPSIS"><A NAME="2">SYNOPSIS
</A></A></H1>
<PRE> float faceforward(float N, float I, float Ng);
float1 faceforward(float1 N, float1 I, float1 Ng);
float2 faceforward(float2 N, float2 I, float2 Ng);
float3 faceforward(float3 N, float3 I, float3 Ng);
float4 faceforward(float4 N, float4 I, float4 Ng);
half faceforward(half N, half I, half Ng);
half1 faceforward(half1 N, half1 I, half1 Ng);
half2 faceforward(half2 N, half2 I, half2 Ng);
half3 faceforward(half3 N, half3 I, half3 Ng);
half4 faceforward(half4 N, half4 I, half4 Ng);
fixed faceforward(fixed N, fixed I, fixed Ng);
fixed1 faceforward(fixed1 N, fixed1 I, fixed1 Ng);
fixed2 faceforward(fixed2 N, fixed2 I, fixed2 Ng);
fixed3 faceforward(fixed3 N, fixed3 I, fixed3 Ng);
fixed4 faceforward(fixed4 N, fixed4 I, fixed4 Ng);
</PRE>
<H1><A NAME="PARAMETERS"><A NAME="3">PARAMETERS
</A></A></H1>
<DL>
<DT><STRONG>N
</STRONG></DT>
<DD>
<P>
Peturbed normal vector.
</P>
<DT><STRONG>I
</STRONG></DT>
<DD>
<P>
Incidence vector (typically a direction vector from the eye to a vertex).
</P>
<DT><STRONG>Ng
</STRONG></DT>
<DD>
<P>
Geometric normal vector (for some facet the peturbed normal belongs).
</P>
</DD></DL>
<H1><A NAME="DESCRIPTION"><A NAME="4">DESCRIPTION
</A></A></H1>
<P>
Returns a (peturbed) normal as-is if a vertex's eye-space position
vector points in the opposite direction of a geometric normal, otherwise
return the negated version of the (peturbed) normal
</P>
<P>
Mathematically, if the dot product of <I>I</I> and <I>Ng</I> is negative, <I>N</I>
is returned unchanged; otherwise -<I>N</I> is returned.
</P>
<P>
This function is inspired by a RenderMan funciton of the same name though
the RenderMan version has only two parameters.
</P>
<H1><A NAME="REFERENCE_IMPLEMENTATION"><A NAME="5">REFERENCE IMPLEMENTATION
</A></A></H1>
<P>
<B>faceforward</B> for <B>float3</B> vectors could be implemented this way:
</P>
<PRE> float3 faceforward( float3 N, float3 I, float Ng )
{
return dot(I, Ng) < 0 ? N : -N;
}
</PRE>
<H1><A NAME="PROFILE_SUPPORT"><A NAME="6">PROFILE SUPPORT
</A></A></H1>
<P>
<B>refract</B> is supported in all profiles.
</P>
<H1><A NAME="SEE_ALSO"><A NAME="7">SEE ALSO
</A></A></H1>
<P>
<A HREF="dot.html"><I>dot</I></A>, <A HREF="reflect.html"><I>reflect</I></A>, <A HREF="refract.html"><I>refract</I></A>, <A HREF="normalize.html"><I>normalize</I></A>
</P>
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