Severi Salminen <sev### [at] not_thissibafi> wrote:
> In FAQ at 
> http://tag.povray.org/povQandT/languageQandT.html#blurredreflection it 
> is suggested that a good blurred reflection can be achieved using 
> averaged textures. That is true, but they can also be achieved a lot 
> faster using normals, for example:

  The blur trick uses normals as well, but it has a couple of advantages
compared to your suggested method:

  - Your suggestion requires quite heavy antialiasing to look good.
    This is a nuisance for several reasons. It makes rendering slower
    than necessary, and not only when rendering the object in question
    (your suggestion is *not* faster than the averaged textures trick due
    to this) but in the whole scene: Everything else will be antialiased
    heavily as well (which sometimes is good, but more often than not it
    will just be a waste of time since a lighter antialiasing often gives
    a result which is good enough).
      The trick works even without antialiasing (and antialiasing only
    makes it look better) and achieves the same result (because it also
    is based on normals) or even better.

  - Your suggestion produces a grainy blur. Sometimes this is the desired
    effect, but such grainy blur is also possible with the trick (but
    without the need for heavy antialiasing).
      The good thing is, however, that also smooth blur is possible (which
    is achieved by making all the normals go to the same directions in all
    points, which is achieved by scaling the normals large instead of small).

  - It's easy to control how many reflected rays are sent to calculate the
    blurred reflection with the trick. With your suggestion you don't have
    practically any control on this. (The only way to be sure that a certain
    number of reflected rays is always calculated would be to force
    antialiasing on each pixel, but that would be quite extreme since it
    would be done on the whole image and not only on the part where the
    reflecting object is located.)

-- 
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}//  - Warp -

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