Andy, andy... you won't be getting much popularity here tossing around these
rough arguments...

Orchid Win7 v1 <voi### [at] devnull> wrote:
> And then, of course, I discovered POV-Ray.

you discovered povray after Cinema 4D and quake... okey, dokey...

> While computer games amuse
> themselves drawing polygons really, really fast, POV-Ray directly
> simulates things like curved surfaces, 3D textures, reflection,
> refraction, and so forth.

yeah, now put povray to directly simulate the curved surfaces of a woman's body.

You may use parametric surfaces if writing the right isosurface function is
proving too much of a challenge.


> But now we have the so-called unbiased renderers, the path tracers,
> whatever you want to call them. With POV-Ray I need to configure photon
> maps and set up area lights and waste hours tweaking and tuning
> radiosity parameters. And then I see a demo that runs IN A FRIGGING WEB
> BROWSER which uses my GPU to almost instantly render a Cornell box that
> would take multiple hours to draw with POV-Ray.

Truth be told, a cornell box today doesn't take even a minute in povray...

> I will freely admit, however, that almost all of the actual demo images
> are still suspiciously grainy. Which suggests that for "real" scenes,
> rendering still isn't instant. For example,
>
> http://tinyurl.com/87oyfmh

Scenes like that may take several hours on CPU, just like raytraced scenes in
the old days.

> You'd need some insane radiosity settings to get that out of POV-Ray.
> I'm not sure if it's even /possible/ to get that glow around the light
> sources.

the glow most likely is just a post-processing 2D effect.

> On the other hand, no one can deny the image is slightly grainy
> in places.

I prefer film grain rather than ugly splotches every corner.  Also, a  night
shot like that will look noisy in an actual photograph too.  You either get the
best lenses possible or let it render for more time to gather more light
samples.


> And then I see something like this:
>
> http://tinyurl.com/7r72o7k
>
> At first glance, this is an amazing, near-photographic image. And then I
> notice THE POLYGONS! IT BURNS!!! >_< KILL IT WITH FIRE!

I don't note any polygons in particular, but the surfaces are all too flat and
regular, denouncing it as CG.  Luxrender, like povray these days, is
conspicuously lacking in true artists rather than programmers trying to show off
the software.

That scene, I believe, took about 1 day or 2 to be that smooth if memory serves
me well...

This is a better scene, from an artist I truly enjoy, Enrico Cerica:

http://enricocerica.cgsociety.org/gallery/962953/

Modeled in Blender, rendered in Octane, a commercial path tracer that runs
exclusively on GPU.

Truly a photograph of a virtual environment.


> Now here's an interesting question: Does anybody know how this stuff
> actually /works/?
>
> In the simplest form, it seems that for each pixel, you shoot a ray
> backwards, and let it bounce off things at random angles (subject to how
> rough or smooth the materials are) until it finds a light source. For
> one ray, the result is pretty random. But average together a few
> bazillion rays, and slowly the random speckle converges to a beautiful,
> smooth (but slightly grainy) image.

http://www.pbrt.org/

The book explains all and source code for the renderer is GPLed.  In fact, it's
the base for Luxrender.


> Wikipedia asserts "Contrary to popular myth, Path Tracing is /not/ a
> generalisation of ray tracing." This statement makes no sense
> whatsoever. :-P

To me pathtracing looks as much of a generalisation of raytracing as raytracing
was of raycasting (which BTW, is progressively being more used in games for
things like LOD management).  But I believe they were talking about how it is
not simply raytracing with (possibly) infinite ray bouncing.


> Does this paper make /any/ sense to anybody?

certainly not to someone without the particular math and rationale insight. :)

> I'd almost be tempted to write a renderer myself - except that running
> on a CPU, it will undoubtedly take several billion millennia to draw
> anything. (There's a /reason/ nobody has tried this until today...)

No, just a few hours or days like povray back in 1990's.

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