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This one looks good !
I thought that fur could only be rendered through macros !
I am eager to take a look at your script.
> Here's my contribution to the teddy-bear collection. The teddy is from the
> Moray site (thanks for the pointer, Ken) and the fur is my doing. It's kinda
> sparse, but I didn't want a long render (this one was ~30 minutes at 640X480
> AA 0.3 and took 69MB of memory)
> I will now post the first version of my fur generator to text.scene-files.
> Note that it requires the Superpatch.
> Comments, suggestions and questions are welcome!
>
> Margus
>
> [Image]
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>This one looks good !
>
>I thought that fur could only be rendered through macros !
>
<ahem...> It _is_ a macro. 2 macros, actually.
But fur can also be modelled with media - see the post "Did someone say
fur?" by Thomas Willhalm.
Margus
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Vahur Krouverk wrote in message <36E19E92.E46E008F@fv.aetec.ee>...
>
>Super!
>Suggestion: use "back-hair culling" - don't create those fur hairs,
>which are not seen. I don't know, whether this is done already and how
>hard is to do this, but it may provide more hair for camera direction.
It should be possible and potentially very useful. Right now I see 2
problems:
1) reflections may show bald ares;
2) you should see some hairs sprouting from areas that are outside the
camera's FOV (esp. with long hairs);
How to deal with these, I don't know. Suggestions?
Margus
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Well, what I meant is that I thought that fur could be created with a
special feature of Superpatch.
> >This one looks good !
> >
> >I thought that fur could only be rendered through macros !
> >
>
> <ahem...> It _is_ a macro. 2 macros, actually.
> But fur can also be modelled with media - see the post "Did someone say
> fur?" by Thomas Willhalm.
>
> Margus
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I'd be happy to work with you on it. Actually I have a few ideas.. the
first being to add a "culling" keyword (ie you know there is a mirror
somewhere, so you need all the hair) or perhaps to give the vector to
the mirror and calculate off of both. The other is to add a margin to
the occlusion formula. Don't occlude EXACTLY at the point where the
point is no longer visible..occlude 5 degrees further or some such.
Steve
(of course I still need to dl the super patch)
Margus Ramst wrote:
>
> Vahur Krouverk wrote in message <36E19E92.E46E008F@fv.aetec.ee>...
> >
> >Super!
>
>
> >Suggestion: use "back-hair culling" - don't create those fur hairs,
> >which are not seen. I don't know, whether this is done already and how
> >hard is to do this, but it may provide more hair for camera direction.
>
> It should be possible and potentially very useful. Right now I see 2
> problems:
> 1) reflections may show bald ares;
> 2) you should see some hairs sprouting from areas that are outside the
> camera's FOV (esp. with long hairs);
>
> How to deal with these, I don't know. Suggestions?
>
> Margus
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On Sat, 06 Mar 1999 20:45:34 -0500, Stephen Lavedas
<swl### [at] virginia edu> wrote:
>I'd be happy to work with you on it. Actually I have a few ideas.. the
>first being to add a "culling" keyword (ie you know there is a mirror
>somewhere, so you need all the hair) or perhaps to give the vector to
>the mirror and calculate off of both. The other is to add a margin to
>the occlusion formula. Don't occlude EXACTLY at the point where the
>point is no longer visible..occlude 5 degrees further or some such.
>
>Steve
>(of course I still need to dl the super patch)
>
>
>Margus Ramst wrote:
>>
>> Vahur Krouverk wrote in message <36E19E92.E46E008F@fv.aetec.ee>...
>> >
>> >Super!
>>
>>
>> >Suggestion: use "back-hair culling" - don't create those fur hairs,
>> >which are not seen. I don't know, whether this is done already and how
>> >hard is to do this, but it may provide more hair for camera direction.
>>
>> It should be possible and potentially very useful. Right now I see 2
>> problems:
>> 1) reflections may show bald ares;
>> 2) you should see some hairs sprouting from areas that are outside the
>> camera's FOV (esp. with long hairs);
>>
>> How to deal with these, I don't know. Suggestions?
>>
>> Margus
The paper "Computing the antipenumbra of an area light source" by Seth
Teller may be useful here. Consider the mirror, etc as the area
light. The paper is at:
http://www-graphics.stanford.edu/papers/antipenumbra
Jerry Anning
clem "at" dhol "dot" com
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The mirror problem is relatively easy to overcome; a very crude approach
would be to trace a ray from all the corners of the mirror's bounding box.
If the sample point is invisible to all these rays, we can safely deduct
that the point is not visible to the mirror.
Multiple mirrors would still present a problem, but solving that wold get
too complex (parse time is an issue, too). Culling would have to be turned
off in that case.
I just downloaded the paper suggested by Jerry, I'll see if this provides a
more plausible solution...
I can't quite visualize a solution for the second problem. When the angle
between the camera ray and the surface normal is >90 degrees, the point is
not visible (provided that all normals point outwards). But how do I know
how far the point is from the nearest visible point?
The answer may be simple, but I don't have it. Perhaps you would describe
how you'd go about solving it?
Margus
Stephen Lavedas wrote in message <36E1DA3E.44410F86@virginia.edu>...
>I'd be happy to work with you on it. Actually I have a few ideas.. the
>first being to add a "culling" keyword (ie you know there is a mirror
>somewhere, so you need all the hair) or perhaps to give the vector to
>the mirror and calculate off of both. The other is to add a margin to
>the occlusion formula. Don't occlude EXACTLY at the point where the
>point is no longer visible..occlude 5 degrees further or some such.
>
>Steve
>(of course I still need to dl the super patch)
>
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My solution was merely to increase the angle to something like >95
degrees or so until results are good. Actually, I don't think that for
your hair at least that 90 degrees is going to be enough...ie, since the
hair sticks up from the object and is visible beyond the surface. My
solution would draw excess hairs, but fewer than covering the entire
surface
Steve
Margus Ramst wrote:
>
> The mirror problem is relatively easy to overcome; a very crude approach
> would be to trace a ray from all the corners of the mirror's bounding box.
> If the sample point is invisible to all these rays, we can safely deduct
> that the point is not visible to the mirror.
> Multiple mirrors would still present a problem, but solving that wold get
> too complex (parse time is an issue, too). Culling would have to be turned
> off in that case.
> I just downloaded the paper suggested by Jerry, I'll see if this provides a
> more plausible solution...
>
> I can't quite visualize a solution for the second problem. When the angle
> between the camera ray and the surface normal is >90 degrees, the point is
> not visible (provided that all normals point outwards). But how do I know
> how far the point is from the nearest visible point?
> The answer may be simple, but I don't have it. Perhaps you would describe
> how you'd go about solving it?
>
> Margus
>
> Stephen Lavedas wrote in message <36E1DA3E.44410F86@virginia.edu>...
> >I'd be happy to work with you on it. Actually I have a few ideas.. the
> >first being to add a "culling" keyword (ie you know there is a mirror
> >somewhere, so you need all the hair) or perhaps to give the vector to
> >the mirror and calculate off of both. The other is to add a margin to
> >the occlusion formula. Don't occlude EXACTLY at the point where the
> >point is no longer visible..occlude 5 degrees further or some such.
> >
> >Steve
> >(of course I still need to dl the super patch)
> >
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Stephen Lavedas wrote:
>
> My solution was merely to increase the angle to something like >95
> degrees or so until results are good. Actually, I don't think that for
> your hair at least that 90 degrees is going to be enough...ie, since the
> hair sticks up from the object and is visible beyond the surface. My
> solution would draw excess hairs, but fewer than covering the entire
> surface
>
> Steve
With some objects, it would work. With others, it wouldn't. Consider a box.
There is a very sharp change in normal direction at the edge. The
normal/camera difference could be up to 180 degrees, yet the point could lie
next to a visible point and culling shouldn't take place. You could argue that
the existing hairs would obscure this shortcoming. But if the box were very
thin, the lack of hairs on the backside would become visible.
Still, this solution is nice and simple. Anything better would need to have
some kind of a sorting algorithm, I'm afraid. Perhaps I'll let the user
specify a culling angle. 180 degrees - no culling. 0 degrees - nice and bald
:)
Margus
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That is kinda what I was going for, a solution that while not perfect it
is easy to implement. I actually kind of considered the variable angle
as a solution. Just after I posted the message. Let me know how it
turns out.
Steve
Margus Ramst wrote:
>
> Stephen Lavedas wrote:
> >
> > My solution was merely to increase the angle to something like >95
> > degrees or so until results are good. Actually, I don't think that for
> > your hair at least that 90 degrees is going to be enough...ie, since the
> > hair sticks up from the object and is visible beyond the surface. My
> > solution would draw excess hairs, but fewer than covering the entire
> > surface
> >
> > Steve
>
> With some objects, it would work. With others, it wouldn't. Consider a box.
> There is a very sharp change in normal direction at the edge. The
> normal/camera difference could be up to 180 degrees, yet the point could lie
> next to a visible point and culling shouldn't take place. You could argue that
> the existing hairs would obscure this shortcoming. But if the box were very
> thin, the lack of hairs on the backside would become visible.
> Still, this solution is nice and simple. Anything better would need to have
> some kind of a sorting algorithm, I'm afraid. Perhaps I'll let the user
> specify a culling angle. 180 degrees - no culling. 0 degrees - nice and bald
> :)
>
> Margus
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