Alain <kua### [at] videotronca> wrote:
> Le 18-01-12 à 08:53, Motive17 a écrit :
> > clipka <ano### [at] anonymousorg> wrote:
> >> Am 10.01.2018 um 12:18 schrieb Motive17:
> >>> Simple question:
> >>>
> >>> do you know if there is a way for extracting the length of the rays path from
> >>> the light source until the camera?
> >>
> >> If there is only one light source involved, you /could/ use a special
> >> pigment for the objects in your scene that sums up the distance between
> >> the surface and the camera plus the distance between the surface and the
> >> light source.
> >>
> >> Use a function-based pigment, with a function constructed like this:
> >>
> >>      #declare FnDist = function(x,y,z) { sqrt(x*x + y*y + z*z) }
> >>      #declare Fn = function(x,y,z) {
> >>          FnDist(x-xC,y-yC,z-zC) +
> >>          FnDist(x-xL,y-yL,z-zL)
> >>      }
> >>      #declare P = pigment {
> >>          function { Fn(x,y,z)/MaxDistance }
> >>      }
> >>
> >> where <xC,yC,zC> is the location of the camera, <xL,yL,zL> is the
> >> location of the light source, and MaxDistance is the maximum total
> >> distance you want to be able to handle properly.
> >>
> >> Then choose a finish that gives full brightness whenever the surface is
> >> illuminated (regardless of incident light angle):
> >>
> >>      finish { ambient 0 diffuse 1 brilliance 0 }
> >>
> >> Finally, set up the light source to have no distance-based attenuation
> >> (i.e. use `fade_power 0`).
> >>
> >>
> >> This should give you an output image where the brightness of each pixel
> >> corresponds to the distance the light ray has travelled.
> >>
> >>
> >> Make sure to use a high bit depth for the output image, and either use
> >> linear encoding (`File_Gamma=1`) or be aware that your pixel values will
> >> not correspond linearly to distance travelled.
> >
> >
> > Thank you for the reply. This could be a very interesting approach.
> >
> > Maybe a trivial question but...about the values x,y,z in the definition of the
> > function Fn:
> >
> >   Fn = function(x,y,z) {
> >           FnDist(x-xC,y-yC,z-zC) +
> >           FnDist(x-xL,y-yL,z-zL)
> >
> > what do they represent for POV-ray?
> >
> > I was thinking I could introduce a such function directly as a light attenuation
> > function in the definition of light source.
> >
> > What do you think about?
> >
> >
>
> The x, y, z are world centric, with the point <0,0,0> as the origin.
> When evaluating a function, for say, an isosurface or a pigment, it's
> the current point been tested.

Thanks!

Post a reply to this message