1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2<HTML> 3<HEAD> 4<META http-equiv="Content-Type" content="text/html; charset=windows-1252"> 5<META name="GENERATOR" content="Microsoft FrontPage 5.0"> 6<META http-equiv="Content-Style-Type" content="text/css"> 7<LINK rel="stylesheet" type="text/css" href="../../CSS/revolution.css"> 8<TITLE>VECHalfAngle</TITLE> 9</HEAD> 10<BODY> 11<H1 align="left">VECHalfAngle</H1> 12<H2 align="left">C Specification</H2> 13<BLOCKQUOTE><CODE><CODE>#include <revolution/mtx.h></CODE></CODE></BLOCKQUOTE> 14<BLOCKQUOTE><CODE><CODE>void VECHalfAngle ( const Vec* <EM>a</EM>, const Vec* <EM>b</EM>, Vec* <EM>half</EM> );</CODE></CODE></BLOCKQUOTE> 15<H2 align="left">Arguments</H2> 16<DIV align="left"> 17<TABLE border="1" cellpadding="3" cellspacing="0.1"> 18 <TBODY> 19 <TR> 20<TD width="120" bgcolor="#ffffe8"><CODE><STRONG><EM>a</EM></STRONG></CODE></TD> 21<TD width="520">Pointer to incident <A href="../structures/Vec_VecPtr.html"><CODE>Vec</CODE></A>. Must point from the light source to the reflection surface. <br><code><em><strong>a</strong></em></code> does not have to be a unit vector.</TD> 22 </TR> 23 <TR> 24<TD width="120" bgcolor="#ffffe8"><CODE><STRONG><EM><em><strong><code>b</code></strong></em> </EM></STRONG></CODE></TD> 25<TD width="520">Pointer to the line-of-sight <A href="../structures/Vec_VecPtr.html"><CODE>Vec</CODE></A>. Must point from the eyepoint to the surface.<br><code><em><strong>b</strong></em></code> does not have to be a unit vector.</TD> 26 </TR> 27 <TR> 28<TD width="120" bgcolor="#ffffe8"><CODE><STRONG><EM>half</EM></STRONG></CODE></TD> 29<TD width="520">Pointer to resultant half-angle unit vector. <code><em><strong>half</strong></em></code> points away from the surface in a direction halfway between the light source and the eyepoint. Acceptable if <code><em><strong>half</strong></em> = <em><strong>a</strong></em></code> or <code><em><strong>half</strong></em> = <em><strong>b</strong></em></code>.</TD> 30 </TR> 31 </TBODY> 32</TABLE> 33</DIV> 34<H2 align="left">Return Values</H2> 35<P align="left">None.</P> 36<H2 align="left">Description</H2> 37<P>This function calculates the vector that is half way between <CODE><EM><STRONG>a</STRONG></EM></CODE> and <CODE><EM><STRONG>b</STRONG></EM></CODE>. This half-angle vector is useful in calculating specular reflections. The reflection from the surface is interpreted as pointing in the same general direction as the line-of-sight. </P> 38<P><CODE><EM><STRONG>a</STRONG></EM></CODE> and <CODE><EM><STRONG>b</STRONG></EM></CODE> do not have to be unit vectors. Both vectors are assumed to be pointing toward the surface from the light source or eyepoint. Local copies of these vectors are positively/negatively reversed and normalized, and the head of one vector is connected to the tail of the other. </P> 39<P><CODE><EM><STRONG>half</STRONG></EM></CODE> is calculated as a unit vector located halfway between the light reflecting from the surface and the line-of-sight. </P> 40 41 42<H2 align="left">See Also</H2> 43<P align="left"><A href="../structures/Vec_VecPtr.html"><CODE>Vec, VecPtr, </CODE></A></P> 44<P align="left"><CODE><A href="VECAdd.html">VECAdd</A>, <A href="VECReflect.html">VECReflect</A></CODE></P> 45<H2>Revision History</H2> 46<P>2006/03/01 Initial version.</P> 47<hr> 48<P>CONFIDENTIAL</p> 49</BODY> 50</HTML>