secondary ray 2005-03-30 - By Jim Rothrock
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Gerbrand Nel wrote:
<blockquote cite="mid003201c53503$4509c790$1600a8c0@(protected)" type="cite">
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<div><font face="Arial" size="2">still feels like it shouldn't work
this way, if I make something 100 % transparent but still have
highlights running on it, everything behind that object should be a
secondary ray... because it's a refraction on the transparent object,
even if the index of refraction is 1 ??? does anyone else agree?????
the funny thing is it starts working the moment you change the index of
refraction. usefull sometimes but isn't that what the sprite shader is
for????</font></div>
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Without having the source code to the shader you are using, I can make
a guess about what is happening. If the relative index of refraction
is not 1.0, the ray direction must change, so the shader calls
mi_trace_refraction(). If the relative IOR is 1.0, the ray direction
will not change, so mi_trace_transparent() is called instead. This is
a speed optimization. mi_trace_transparent() will have approximately
the same effect as mi_trace_refraction(result, state,
&state->dir), but transparency rays are considered to be primary
rays. From the mental ray documentation:<br>
<br>
<p><tt> miRAY_PRIMARY(raytype)</tt><br>
is true if the raytype is a primary or a
transparency ray.<br>
</p>
<pre class="moz-signature" cols="72">--
Jim Rothrock | Stan Winston Digital | <a class="moz-txt-link-abbreviated" href=
"mailto:jimr@(protected)">jimr@(protected)</a>
</pre>
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