Tim Cook <z99### [at] gmailcom> wrote:
> >    I think you are confusing the brightest part of diffuse reflection with
> > the brightest part of a specular highlight. They are not at the same place.
> > The former is at the point where the surface is directly facing the light
> > source (and it does not depend on the position of the camera), while the
> > latter is where the angle between the normal vector of the surface and
> > the light source is the same as the angle between the normal vector and
> > the camera (which means that the location of the highlight depends on the
> > location of the camera, and thus moves if the camera is moved).

> ...and this, which I'm finding hard to visualise, somehow.  Rather, I 
> /can/, but understanding of what's happening in regards to 
> light/object/camera relative loci is escaping me.  An animation would do 
> wonders (and not just for me, perhaps?)...

  You don't need an animation to visualize the difference. Consider the
following:

//----------------------------------------------------
camera { location -z*6.5 angle 25 look_at 0 }
light_source { y*100, 1 }
sphere
{ 0, 1
  pigment { rgb <1, .5, .25> }
  finish { specular 1 roughness .01 }
}
//----------------------------------------------------

  The brightest part of the (diffusely illuminated) surface is at the very
top, because the light source is right above the sphere (and the camera is
on the z axis). However, the specular highlight is not at the top, but lower
(more precisely where the angle between the normal vector and the light
source is the same as with the camera).

-- 
                                                          - Warp

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