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>GXInitLightAttn</TITLE> 9</HEAD> 10<BODY> 11<H1 align="left">GXInitLightAttn</H1> 12 13<H2>Syntax</H2> 14<dl><dd><pre class="construction"> 15#include <revolution/gx.h> 16 17void GXInitLightAttn( 18 <A href="../Structures/GXLightObj.html">GXLightObj</A>* lt_obj, 19 f32 a0, 20 f32 a1, 21 f32 a2, 22 f32 k0, 23 f32 k1, 24 f32 k2 ); 25</pre></dd></dl> 26 27<H2>Arguments</H2> 28<TABLE class="arguments" border="1" > 29 <TBODY> 30 <TR> 31<TH>lt_obj</TH> 32<TD>Pointer to a light object.</TD> 33 </TR> 34 <TR> 35<TH>a0</TH> 36<TD>Angular attenuation coefficient.</TD> 37 </TR> 38 <TR> 39<TH>a1</TH> 40<TD>Angular attenuation coefficient.</TD> 41 </TR> 42 <TR> 43<TH>a2</TH> 44<TD>Angular attenuation coefficient.</TD> 45 </TR> 46 <TR> 47<TH>k0</TH> 48<TD>Distance attenuation coefficient.</TD> 49 </TR> 50 <TR> 51<TH>k1</TH> 52<TD>Distance attenuation coefficient.</TD> 53 </TR> 54 <TR> 55<TH>k2</TH> 56<TD>Distance attenuation coefficient.</TD> 57 </TR> 58 </TBODY> 59</TABLE> 60 61<H2>Return Values</H2> 62<P>None.</P> 63 64<H2>Description</H2> 65<P>This function sets coefficients used in the lighting attenuation calculation for a given light object. The application must allocate the memory for the light object. The arguments <SPAN class="argument">a0</SPAN>, <SPAN class="argument">a1</SPAN>, and <SPAN class="argument">a2</SPAN> are used for angular (spotlight) attenuation. The coefficients <SPAN class="argument">k0</SPAN>, <SPAN class="argument">k1</SPAN>, and <SPAN class="argument">k2</SPAN> are used for distance attenuation. The attenuation function is:</P> 66<P><CITE><EM>atten = <U>clamp0(<STRONG> a2</STRONG> * aattn^2 +</U></EM><U> <EM><STRONG>a1</STRONG></EM> * <EM>aattn +</EM> <EM><STRONG>a0</STRONG></EM> )</U><BR> <EM><STRONG> k2</STRONG></EM> <EM>* d^2 +</EM> <EM><STRONG>k1</STRONG></EM> * <EM>d +</EM> <STRONG><EM>k0</EM></STRONG></CITE></P> 67<P>where <EM>aattn</EM> is the cosine of the angle between the light direction and the vector from the light position to the vertex. Likewise, <EM>d</EM> is the distance from the light position to the vertex when the channel attenuation function is <CODE>GX_AF_SPOT</CODE>. The light color will be multiplied by the <EM>atten</EM> coefficient when the attenuation function for the color channel referencing this light is set to <CODE>GX_AF_SPOT</CODE> (see the <A href="GXSetChanCtrl.html"><CODE>GXSetChanCtrl</CODE></A> function).</P> 68<P>All coefficients are represented with a 20-bit floating point format (1-bit sign, 8-bit exponent, and 11-bit significand) in the hardware, as for other arguments associated with vertex lighting. Be aware of possible rounding errors as a result.</P> 69<P>The <A href="GXInitLightSpot.html"><CODE>GXInitLightSpot</CODE></A> function is a convenient way to set the angle attenuation coefficients based on several spotlight types. The <A href="GXInitLightDistAttn.html"><CODE>GXInitLightDistAttn</CODE></A> function is a handy way to set the distance attenuation coefficients using one of several common attenuation functions.</P> 70<P>When the channel attenuation function is set to <CODE>GX_AF_SPEC</CODE>, the <EM>aattn</EM> and <EM>d</EM> arguments are equal to the dot product of the visual space vertex normal and the half-angle vector set by the <A href="GXInitSpecularDir.html"><CODE>GXInitSpecularDir</CODE></A> function.</P> 71<P>The <A href="GXInitLightShininess.html"><CODE>GXInitLightShininess</CODE></A> macro can be easily used to set attenuation parameters for specular lights.</P> 72<P>Be aware that this function does not load any hardware registers directly. To load a light object into a hardware light, use the <A href="GXLoadLightObjImm.html"><CODE>GXLoadLightObjImm</CODE></A> or <A href="GXLoadLightObjIndx.html"><CODE>GXLoadLightObjIndx</CODE></A> function.</P> 73 74<H2>See Also</H2> 75<P class="reference"> 76<A href="GXInitLightAttnA.html">GXInitLightAttnA</A>, 77<A href="GXInitLightAttnK.html">GXInitLightAttnK</A>, 78<A href="GXInitLightSpot.html">GXInitLightSpot</A>, 79<A href="GXInitLightDistAttn.html">GXInitLightDistAttn</A>, 80<A href="GXInitLightShininess.html">GXInitLightShininess</A>, 81<A href="GXSetChanCtrl.html">GXSetChanCtrl</A>, 82<A href="GXLightObjInitFlow.html">GXLightObj Initialization Flow</A> 83</P> 84 85<H2>Revision History</H2> 86<P> 872006/03/01 Initial version.<br> 88</P> 89 90<hr><p>CONFIDENTIAL</p></body> 91</HTML>