Hi!

I want to texture the part of an object that is  under an "overhang"
differently from the rest. I.e. I would like to use a slope y (or was
it -y?) and when it is negative, I want to give the part in -y-direction a
different pigment even if the slope is positive again.

Is it possible in MegaPov itself?

Hope I was clear enough ;-),

Marc-Hendrik

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Marc-Hendrik Bremer wrote:
> 
> Hi!
> 
> I want to texture the part of an object that is  under an "overhang"
> differently from the rest. I.e. I would like to use a slope y (or was
> it -y?) and when it is negative, I want to give the part in -y-direction a
> different pigment even if the slope is positive again.
> 
> Is it possible in MegaPov itself?
> 

Sounds tricky, if i understand it right it should look like an object
covered by a thin layer of snow (which would not reach the parts covered
by overhangs).  

I posted a simple snowing macro some time ago, but it would be slow and
also modifies the geometry (you could use the object pattern to avoid
this)

If your object is an isosurface or another simple mathematical shape, you
could try to construct a function pattern for that, but it seems quite
difficult to me.

Anyway it would be quite possible to add this as a new internal pattern to
povray.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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Christoph Hormann schrieb in Nachricht <3A6052C4.57639B46@gmx.de>...
>Sounds tricky, if i understand it right it should look like an object
>covered by a thin layer of snow (which would not reach the parts covered
>by overhangs).
>

Hm yes, I thought the other way round, but that doesn't matter.

>I posted a simple snowing macro some time ago, but it would be slow and
>also modifies the geometry (you could use the object pattern to avoid
>this)
>

I've found the macro and remember the related image. But if there is another
sulotion, I would prefer not to use trace() for this problem. The Object i'm
thinking of is quite complicate and I would have to call trace more than
once for every "row". Seems quite slow to me (and I never used it before
:-)).

>If your object is an isosurface or another simple mathematical shape, you
>could try to construct a function pattern for that, but it seems quite
>difficult to me.

Well, it's made out of some Isos, but I wouldn't want to try to make one
single function out of them.

>
>Anyway it would be quite possible to add this as a new internal pattern to
>povray.


If there is no other easy way, that would be quite usefull IMHO.  If it
would be possible to specify a "delay" for the slope dependent texture that
would suffice, I think. There should be a way to specify what should be
delayed (positiv/nagative or no slope), too. But I'm no programmer (at least
not in C), so I'll have to wait and see ....

Thanks,

Marc-Hendrik

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Marc-Hendrik Bremer wrote:
> 
> If there is no other easy way, that would be quite usefull IMHO.  If it
> would be possible to specify a "delay" for the slope dependent texture that
> would suffice, I think. There should be a way to specify what should be
> delayed (positiv/nagative or no slope), too. But I'm no programmer (at least
> not in C), so I'll have to wait and see ....
> 

I'm not sure what you mean by "delay".  The internal version i thought of
could just test, whether there is some part of the object 'above' a point
and select the right texture.  

I don't know how your object is shaped, but if there is only 'one layer of
overhangs', you could use a translated object pattern to simulate it.  

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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Christoph Hormann schrieb in Nachricht <3A60662D.FBDFCBE5@gmx.de>...
>I'm not sure what you mean by "delay".  The internal version i thought of
>could just test, whether there is some part of the object 'above' a point
>and select the right texture.


I thought in the directon that all neccessary (for my problem) info is given
with the slope - but not at the right place.

I'm working on a building and want to "age" it. But under the overhanging
roof and some beams it would be cleaner then further "down". If the Info of
the slope could be holded while the pattern "moves further down" (nothing is
moving - I know), then I could design the textures accordingly. "delay" was
probably not right.

But your suggestion is as good as mine, if one could freely determine where
"above" is.

It would be also great, if one could #declare the "slope-pigment" of one
object for use as a texture_map on another one .

>
>I don't know how your object is shaped, but if there is only 'one layer of
>overhangs', you could use a translated object pattern to simulate it.

In this case it is the above mentioned building. In wich way is the
information if one point is inside or outside an object usefull for this
case?


Marc-Hendrik

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In article <3a604230@news.povray.org>, "Marc-Hendrik Bremer" 
<Mar### [at] t-onlinede> wrote:

> I want to texture the part of an object that is  under an "overhang"
> differently from the rest. I.e. I would like to use a slope y (or was
> it -y?) and when it is negative, I want to give the part in -y-direction a
> different pigment even if the slope is positive again.

I'm not sure what you mean..."when it is negative...", "...even if the 
slope is positive again."
The slope is either negative or positive (actually, it goes from 0 to 
1). Do you want a texture that covers the downward facing area as well 
as part of the upward-facing area? That should be easy to do simply by 
making your blend map partially solid. For example:
slope y
*_map {
    [0 Bottom]
    [0.5 Bottom]
    [0.6 Top]
    [1 Top]
}

Just remember that slope varies "between (and including) 0.0 and 1.0, 
where 0.0 is most negative slope (surface normal points in negative 
vector direction), 0.5 corresponds to a vertical slope (surface normal 
and slope vector form 90 degree angle) and 1.0 is horizontal with 
respect to the slope vector (surface normal parallel to slope vector)".

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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Marc-Hendrik Bremer wrote:
> 
> I thought in the directon that all neccessary (for my problem) info is given
> with the slope - but not at the right place.
> 
> I'm working on a building and want to "age" it. But under the overhanging
> roof and some beams it would be cleaner then further "down". If the Info of
> the slope could be holded while the pattern "moves further down" (nothing is
> moving - I know), then I could design the textures accordingly. "delay" was
> probably not right.
> 

That makes it much clearer.

> 
> In this case it is the above mentioned building. In wich way is the
> information if one point is inside or outside an object usefull for this
> case?
> 

For example if the building has a flat roof of any shape, you can use the
object pattern in the height of the roof to determine whether something is
covered by the roof or not.

I posted a picture of some new pattern i made to p.b.i.  Combined with
regular slope pattern it could meet your purpose.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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