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scott wrote:
>> this is an insanely amazing Crysis mod shot too:
>>
>>
http://www1.picturepush.com/photo/a/1578869/1024/Crysis/crysis64-2009-04-11-19-45-23-44.png
>>
>
> Imagine how long that would take to render in POV, media, DOF,
> refraction! And I don't think the result would be *that* different
> (maybe the refraction would look slightly different, but a normal person
> probably couldn't tell which one was correct, especially during animation).
It wouldn't have all those glitches that games have though. (Like grass
that rotates as you run past it, or "mist" that has sharp edges where it
intersects things.)
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On Thu, 24 Sep 2009 09:25:52 +0100, Invisible wrote:
> I was under the impression that splines can describe any possible
> surface.
"When the only tool you have is a hammer, everything looks like a nail."
In my current sleep-deprived state, that seems a relevant quote. It may
not after I go to bed, sleep, wake up, shower, and come back up here in
the morning. But right now it seems relevant.
Jim ZZZZzzzzzzzzzzzzzzzzzzzzzzzz.................
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>> I don't understand the fascination with perfect mathematically described
>> surfaces, they are inflexible and slow to render.
>
> Really? I was under the impression that splines can describe any possible
> surface.
How do you render a splined surface directly? Even POV converts them to
triangles first!
> Triangles, on the other hand, can only give a crude approximation to
> curves.
In practice display devices are made of pixels, so using triangles you can
always get exactly the same output as using the true curve. Have you ever
seen any "crude approximations" to curves in film CG?
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>> Really? I was under the impression that splines can describe any
>> possible surface.
>
> How do you render a splined surface directly? Even POV converts them to
> triangles first!
It's news to me that POV supports splines in the first place.
>> Triangles, on the other hand, can only give a crude approximation to
>> curves.
>
> In practice display devices are made of pixels, so using triangles you
> can always get exactly the same output as using the true curve.
Only if you have the original curve to hand.
> Have you ever seen any "crude approximations" to curves in film CG?
Have you ever seen any curved surfaces in computer games?
If you *insist* on using triangles, you're going to need a hell of a lot
of them to fake the appearence of a good curve. That means you either
need a triangle mesh of absurd dimensions, or you need to generate the
triangles on the fly.
What all known computer games do is use a static, very low resolution
triangle mesh and then smother it with lashes of low-level trickery to
give a vague semblance of curvature.
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>> Imagine how long that would take to render in POV, media, DOF,
>> refraction! And I don't think the result would be *that* different (maybe
>> the refraction would look slightly different, but a normal person
>> probably couldn't tell which one was correct, especially during
>> animation).
>
> It wouldn't have all those glitches that games have though. (Like grass
> that rotates as you run past it, or "mist" that has sharp edges where it
> intersects things.)
I don't think modern games have those glitches anymore, the grass is true 3D
geometry not just billboards, and the mist billboards usually compare depths
of existing pixels to avoid the hard edges with geometry. Some games even
have true 3D volume textures and rendering for smoke and mist, I don't know
if Crysis uses this or just cheats with multiple billboards. Maybe the
glitches you mention are on a game from 5 years ago or on a very badly
written modern one.
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> It's news to me that POV supports splines in the first place.
It does bezier patches which are the closest you are going to get to
describing "any curved surface" mathematically.
> Only if you have the original curve to hand.
What if you designed the curve by seeing how it turned out after
sub-divison? Blender works like this, you can edit the vertices of a very
rough triangle mesh and see how the perfectly smooth surface reacts in real
time. You are then defining the "original curve" by the crude mesh.
> If you *insist* on using triangles, you're going to need a hell of a lot
> of them to fake the appearence of a good curve. That means you either need
> a triangle mesh of absurd dimensions, or you need to generate the
> triangles on the fly.
Exactly. This is what all film-quality renderers do.
> What all known computer games do is use a static, very low resolution
> triangle mesh and then smother it with lashes of low-level trickery to
> give a vague semblance of curvature.
Of course, because that method gets the highest quality output in realtime.
And it's very easy to have two (or more) versions of a mesh at different
resolutions, eg for stills rendering, close-up real-time rendering, far away
rendering etc. When you have a mathematical surface rendered directly it's
very difficult to speed it up!
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scott wrote:
>>> Imagine how long that would take to render in POV, media, DOF,
>>> refraction! And I don't think the result would be *that* different
>>> (maybe the refraction would look slightly different, but a normal
>>> person probably couldn't tell which one was correct, especially
>>> during animation).
>>
>> It wouldn't have all those glitches that games have though. (Like
>> grass that rotates as you run past it, or "mist" that has sharp edges
>> where it intersects things.)
>
> I don't think modern games have those glitches anymore, the grass is
> true 3D geometry not just billboards, and the mist billboards usually
> compare depths of existing pixels to avoid the hard edges with
> geometry. Some games even have true 3D volume textures and rendering
> for smoke and mist, I don't know if Crysis uses this or just cheats with
> multiple billboards. Maybe the glitches you mention are on a game from
> 5 years ago or on a very badly written modern one.
HalfLife 2: Episode 2 has mist in one section. Looks really
impressive... until it intersects something.
Mind you, POV-Ray has the exact same problem, until you turn the
settings up so high that it takes 82+ hours to render a single frame...
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Ever heard of subdivision surfaces, Andrew? You can get a perfectly
round sphere out of a plain cube cage by specifying up to 5 iterations.
This is the norm in the industry, and there's also NURBS.
Pixar got its own gig with REYES in Renderman, basically an automatic
triangulator breaking down every geometry on screen into triangles until
they are less than one pixel wide in the final resolution. It probably
breaks them down by subdivision as well, since one of the well-known
algorithms has the name of one of Pixar founding fathers...
No one designs multibillion triangle meshes by carefully moving them one
by one.
BTW:
http://www.3d-coat.com/v3_voxel_sculpting.html
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nemesis wrote:
> Ever heard of subdivision surfaces, Andrew? You can get a perfectly
> round sphere out of a plain cube cage by specifying up to 5 iterations.
Yes. But the resulting surface can only be controlled by the 8 original
cube corners. That's not much control.
> No one designs multibillion triangle meshes by carefully moving them one
> by one.
And yet, in all known editors, moving triangle corners around one at a
time is the only available editing operation...
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Invisible wrote:
> nemesis wrote:
>> Ever heard of subdivision surfaces, Andrew? You can get a perfectly
>> round sphere out of a plain cube cage by specifying up to 5 iterations.
>
> Yes. But the resulting surface can only be controlled by the 8 original
> cube corners. That's not much control.
If you need refinement, you do loop cuts over the control cage and extrude.
>> No one designs multibillion triangle meshes by carefully moving them
>> one by one.
>
> And yet, in all known editors, moving triangle corners around one at a
> time is the only available editing operation...
You have your head in the 80's. Do you ever click on the links I provide?
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