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When I define the normals at the corners of a smooth_triangle,
how exactly is the interpolation done -- is it a linear weighted sum of
the corner vectors, or something subtler? Is each normal vector first
converted to a unit vector?
(Yes, I have a project in mind which could depend on such subtleties.)
--
Anton Sherwood, http://www.ogre.nu/
"How'd ya like to climb this high *without* no mountain?" --Porky Pine
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Wasn't it Anton Sherwood who wrote:
>When I define the normals at the corners of a smooth_triangle,
>how exactly is the interpolation done -- is it a linear weighted sum of
>the corner vectors, or something subtler? Is each normal vector first
>converted to a unit vector?
I don't know what the rule is, but it doesn't appear to be linear
weighted sum.
This code looks at the normals along one edge of a particular smooth
trinagle. The "N" vector is what trace() finds at points along one edge,
and "A" is the vnormalized linear weighted sum. There are distinct
differences.
#version 3.6;
camera {location <0,0,-10>*10 look_at <0,0,0> angle 50}
light_source {<-30, 100, -30> color rgb 1}
#include "strings.inc"
#declare N1 = <0, 0.7071, -0.7071>;
#declare N2 = <0, -0.8664, -0.5>;
#declare N3 = <0, -0.5, -0.8664>;
#declare T = smooth_triangle {
< 0, 30, 0> N1
< 30, 0, 0> N2
< 0, 0, 0> N3
pigment {rgb 2}
}
object {T}
#declare Y=0;
#while (Y<=30)
#declare N=<0,0,0>;
#declare P = trace(T, <0,Y,-100>, <0,0,1>, N);
#declare A = N1*(Y/30) + N3*(1-Y/30);
#debug concat( str(Y,0,0),": ",VStr(N)," ", VStr(vnormalize(A)), "\n")
#declare Y=Y+1;
#end
--
Mike Williams
Gentleman of Leisure
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