Hi everyone,

I hit a strange "problem" with 'functions' or at least I can't figure out
what's wrong in my code:

I tried to use a function as a pigment and I'd like to use the normal vector
(or, to be more prezicely, the angle at with the camera ray hits the
surface) of the surface in my pigment-function, but I can't get it working.

Here's a short piece of code that shows the problem:

camera

{

location <0,5,-10>

look_at <0,0,0>

}

background { color rgb <0,0,1> }

/********************************************************************/

#declare test_pigment = pigment { checker }

#declare f_pigment = function { pattern { checker } }

#declare function_pigment = pigment { function { f_pigment(x,y,z) } }

/********************************************************************/


plane

{

y,-1

pigment { function_pigment }

finish { ambient 1 }

clipped_by { plane { x,0 } }

}

plane

{

y,-1

pigment { test_pigment }

finish { ambient 1 }

clipped_by { plane { -x,0 } }

}

sphere

{

<-2.5,1,0>,2

pigment { function_pigment }

finish { ambient 1 }

}

sphere

{

<2.5,1,0>,2

pigment { test_pigment }

finish { ambient 1 }

}

this works as expected, but when I change the pattern to slope:

/********************************************************************/

#declare test_pigment = pigment { slope { <0,5,-10> } }

#declare f_pigment = function { pattern { slope { <0,5,-10> } } }

#declare function_pigment = pigment { function { f_pigment(x,y,z) } }

/********************************************************************/

I get the following error:

"Parse Error: No matching } in 'pattern', slope found instead"

I also tried it with a pigment instead of a pattern:

/********************************************************************/

#declare test_pigment = pigment { checker }

#declare f_pigment = function { pigment { test_pigment } }

#declare function_pigment = pigment { function { f_pigment(x,y,z).grey } }

/********************************************************************/

and again, with the checker pigment it works just fine, but when

switching to the slope-pigment:

/********************************************************************/

#declare test_pigment = pigment { slope { <0,5,-10> } }

#declare f_pigment = function { pigment { test_pigment } }

#declare function_pigment = pigment { function { f_pigment(x,y,z).grey } }

/********************************************************************/

the left side of the image is black (the function seems to return zero all
the time)

Do you know if this is a limitation of the renderer or if there's something
wrong with the code?

As far as I understand, the only values passed to functions are the x/y/z
coordinates of the ray/shape intersection. Is there a way to use other
values like the surface normal, derivates, u/v-coordinates, vector of the
ray, etc. in custom functions (like in the Renderman Shaderlanguege) ?

thanks,

-Sascha Ledinsky

Post a reply to this message

Sascha Ledinsky wrote:
> 
> Hi everyone,
> 
> I hit a strange "problem" with 'functions' or at least I can't figure out
> what's wrong in my code:
> 
> [...]
> 
> this works as expected, but when I change the pattern to slope:
> 
> [...]

Since the slope pattern is only defined on the surface of an object it can
only be used in textures and not in functions.

> As far as I understand, the only values passed to functions are the x/y/z
> coordinates of the ray/shape intersection. Is there a way to use other
> values like the surface normal, derivates, u/v-coordinates, vector of the
> ray, etc. in custom functions (like in the Renderman Shaderlanguege) ?

No, there is POVMan: http://www.aetec.ee/fv/vkhomep.nsf/
which supports a subset of renderman shader functionality though.

Christoph

-- 
POV-Ray tutorials, IsoWood include,                 
TransSkin and more: http://www.tu-bs.de/~y0013390/  
Last updated 13 Aug. 2002 _____./\/^>_*_<^\/\.______

Post a reply to this message