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"Tom York" wrote in message
<web.47079017bcc3cc027d55e4a40@news.povray.org>:
> A user-definable function that accepts some information about a scene,
> object, surface or ray and returns information that the renderer then uses
> to modify the shading, illumination, any other aspect of the rendered
> image.
<snip>
Ok, thanks.
> Yes. Although the actual shader language is usually quite low-level (often
> C-like), and therefore not particularly artist-friendly, most applications
> provide a specialised visual editor. These days they are usually based on
> nodes (plug a texture node into a diffuse shading node to get a texture
> mapped diffuse surface, for example). Some systems opt to use layers, but
> it ends up being the same. The systems are very powerful indeed, much more
> powerful than my textured diffuse example.
I do not think that can be called "writing" a shader. And what you describe
seems to me quite similar to what is possible already with the numerous
pigments of POV-Ray. Isn't it?
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Nicolas George <nicolas$george@salle-s.org> wrote:
> I do not think that can be called "writing" a shader. And what you describe
> seems to me quite similar to what is possible already with the numerous
> pigments of POV-Ray. Isn't it?
A shader should be able to, for example, launch additional rays if
necessary.
--
- Warp
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Warp wrote in message <47079ed1@news.povray.org>:
> A shader should be able to, for example, launch additional rays if
> necessary.
Yes, I understood that. And I ask again the question, this time more
precisely:
Is, with any system, a basic non-programmer user, capable of writing a
shader that does more that what is possible with textures and pigments?
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Nicolas George <nicolas$george@salle-s.org> wrote:
> "Tom York" wrote in message
> > Yes. Although the actual shader language is usually quite low-level (often
> > C-like), and therefore not particularly artist-friendly, most applications
> > provide a specialised visual editor. These days they are usually based on
> > nodes (plug a texture node into a diffuse shading node to get a texture
> > mapped diffuse surface, for example). Some systems opt to use layers, but
> > it ends up being the same. The systems are very powerful indeed, much more
> > powerful than my textured diffuse example.
>
> I do not think that can be called "writing" a shader.
Does it matter? As I said, I really doubt POV 4 will include such a visual
editor.
> And what you describe seems to me quite similar to what is possible already
> with the numerous pigments of POV-Ray. Isn't it?
You can look though the archives of this NG to find out. Some of it is not
exactly straightforward. A lot of it is impossible. For an example of the
first, consider a surface whose specularity varies independently of its
roughness. To vary one or the other property requires only a texture_map.
To vary both independently requires two nested levels of texture maps.
That's very clumsy, and hopefully you do not want to vary the diffuse
property as well, or that will be another nesting level working off 8
textures at the lowest level.
For an example of the second, there's plenty of stuff it can't do. Off the
top of my head, apart from launching new rays as Warp suggested (essential
for ambient occlusion), there's ramp/gradient shaders (shaders that can use
the level of illumination to select a colour), using any BDRF apart from
tweaked lambert with tweaked phong specularity, anisotropic highlights. You
can probably find more in the NG archives.
Tom
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Nicolas George <nicolas$george@salle-s.org> wrote:
> Is, with any system, a basic non-programmer user, capable of writing a
> shader that does more that what is possible with textures and pigments?
Well, I think that's a bit like asking "is a basic non-programmer user
capable of writing a #while loop which creates 100 objects in a row?"
Often some appropriate mathematics knowledge would be necessary to
perform certain things (such as knowing which direction to shoot a
ray towards), but POV-Ray could provide auxiliary functions to help
with this (in the same way as currently if you need to know the distance
between two points you don't actually need to know the mathematical
formula to do that because POV-Ray offers you the vlength() function
which you can use for this exact purpose).
Sure, if you have no experience nor knowledge about the relevant
mathematics related to computer graphics, it will be quite more difficult
to write shaders. However, some basic things shouldn't be too hard to
create. And what a better way of learning some math while asking how
to do something specific.
--
- Warp
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> Warp wrote in message <47079ed1@news.povray.org>:
>> A shader should be able to, for example, launch additional rays if
>> necessary.
>
> Yes, I understood that. And I ask again the question, this time more
> precisely:
>
> Is, with any system, a basic non-programmer user, capable of writing a
> shader that does more that what is possible with textures and pigments?
No. Not a "non-programmer". Since a shader consists in taking some
input (point position, normal,...), applying some algorithm, and
returning some final value, it's programming.
However, that's someting a beginner prorammer (someone who already
have the aptitude to create a #macro) should be able to do without
learning C++ first.
IMO, ideally, the shading language should be part, or a subset, of
SDL.
Fabien.
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> Nicolas George <nicolas$george@salle-s.org> wrote:
>> "Tom York" wrote in message
>>> Yes. Although the actual shader language is usually quite low-level (often
>>> C-like), and therefore not particularly artist-friendly, most applications
>>> provide a specialised visual editor. These days they are usually based on
>>> nodes (plug a texture node into a diffuse shading node to get a texture
>>> mapped diffuse surface, for example). Some systems opt to use layers, but
>>> it ends up being the same. The systems are very powerful indeed, much more
>>> powerful than my textured diffuse example.
>> I do not think that can be called "writing" a shader.
>
> Does it matter? As I said, I really doubt POV 4 will include such a visual
> editor.
But if there's a propre shading system, there are chances that someone
someday will write a GUI system like the one described to help designing
shaders.
Fabien.
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Fa3ien wrote in message <47087cc2$1@news.povray.org>:
> However, that's someting a beginner prorammer (someone who already
> have the aptitude to create a #macro) should be able to do without
> learning C++ first.
Ok, to you and to Warp.
But in the scheme I have described, he would be able to write such a
function in Lua.
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Nicolas George <nicolas$george@salle-s.org> wrote:
> But in the scheme I have described, he would be able to write such a
> function in Lua.
IMO using an existing scripting language (which is radically different
from the current SDL), which has not been specifically fine-tuned for use
with POV-Ray, should only be done as a last resort, if it becomes clear
that there's no manpower or resources enough to create a designed-for-pov
scripting language.
--
- Warp
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Fa3ien <fab### [at] yourshoes skynetbe> wrote:
> But if there's a propre shading system, there are chances that someone
> someday will write a GUI system like the one described to help designing
> shaders.
>
> Fabien.
Maybe, depends on the shading language (and on POV4's licensing terms,
although if they do use GPL3 then those will not be an issue). In the
meantime folk'll be stuck writing such things in whatever tertiary language
ends up getting used, under the current plans. I suspect this will annoy
some prospective users of v4, since the one thing that people bother to
mention in the new features of the *renderer* rather than the SDL is more
flexible shading capabilities. If they're inaccessible via the SDL, or at
all inconvenient to use, then many people will think, why bother? Mind you
the suggestions I've seen for the new SDL look so different from the
original SDL that maybe the old user base won't bother with v4 at all.
Tom
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