Loki <nomail@nomail> wrote:
> I haven't tried this yet, it just occurred to me, so I was wondering if
> anyone else has.  To get blurred reflections, is it possible to cheat by
> rendering the scene using a spherical projection from the location of an
> object, then blurring the image in photoshop or whatever, then mapping the
> image back onto the object as a kind of 'env ball' reflection? (as done in
> some other renderers.)

  No, that doesn't work.

  What you are doing there is projecting the scene onto the surface of
the object. That's not a reflection, not even close.

  Simple case: Assume the object is a reflecting plane, like a mirror:
If you look it at a steep angle, eg. 20 degrees, you will see the
scene in front of you reflected in this mirror (there are probably
parts of the scene which you can see directly and reflected).
  However, think what happens if you just project the scene on the plane
like you suggested. It clearly doesn't work.

  It doesn't work correctly even if your reflecting object is more or
less spherical: You will still be just projecting the scene onto the
surface of the object. You will not see any scene which is farther
away from you than the object reflected on the surface of the object
(while with a truely reflecting object you would).
  Simple example: Think about a reflecting sphere on a checkered plane,
and think what happens if the camera is looking at the sphere right
from above: With correct reflections you will see parts of the plane
reflected on the sphere. With your suggestion you won't.

  What scanline-renderers do is not to project the environment map
onto the surface directly, but they take into account the normal
vector of the surface at the current point being rendered plus the
location of the camera, and using basically the same formula for
calculating the direction of the reflected ray in a raytracer, they
get the correspondent pixel from the environment map.
  In POV-Ray you can simulate this by putting the environment map
on the sky_sphere and making the object reflective.

  However, while this give a far more believable reflection, it isn't
perfect either: It assumes that the rest of the scene is infinitely
far away from the reflecting object. If there's any part of the
scene very close to the object, the reflection will not be correct
(the checkers on the plane with the reflected sphere is a good
example).

-- 
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 -

Post a reply to this message