On 27 Jan 1999 07:40:35 -0500, Nieminen Mika <war### [at] cctutfi> wrote:

>Steve  <hor### [at] osuedu> wrote:
>: To see proof of this, turn your ambient to zero on all your
>: surfaces to 0.0 and notice that radiosity no longer has any effect on the
>: rendered scene!!
>
>  I don't understand why this is so bad.
>


It's bad because indirect illumination is then not ADDITIVE to an object's
shading, but in fact is merely a MULTIPLIED factor onto the already existing
ambient coefficient.   So an ambient of zero will "mask the effects" of
radiosity totally.  Radiosity calculations should _replace_, not work with the
ambient value.  It's just like Nathan said, the user still GUESSES what the
brightness of a scene is, rather than radiosity figuring that out for you,
which is what it should do.  

See, ambient was meant to simulate indirect illumination in a scene.
Radiosity actually calculates it.  Do you see why one should then replace the
other? 

Ambient is also meant to be a "self illuminating factor."  This is where it
gets its name.  A surface that emmits light on its own will be "ambient"
becuase it will have some "ambience."  In reaility, no surface really does
this.  To simulate something like a flourescent tube ceiling light, large
ambient values can be used on a cylinder.  

------------
Steve Horn

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