live shadows / crazy ideas I

this will be a thought about some effect which could be achieved using modified ray tracing engine. It has to do with non photorealistick rendering, and magical look to it. Ok, so first of all i am no programer or mathematician of any sorts, so please judge my ideas having that in mind.

First of all what is ray tracing, or ray traced shadows? i will try to describe it in one paragraph, as i understand it myself.

So as far as i understand first we have a viewing plane, from which we “cast a ray” towards an object in a scene. the point where it touches object, we find out properties of object, and return a color value to rendered image, or that particular pixel we started casting ray in view plane. so next is to cast a secondary ray, which starts from a point where first ray touched an object. this ray will go towards a light source. if any object will be in its way, we’ll know that thatlight we just mentioned casts a shadow. i hope its possible to follow me, but actually it doesn’t matter that much, cos anyone could look up ray tracing in wiki. http://en.wikipedia.org/wiki/Ray_tracing

The idea comes to my my mind, is , what if we would treat light differently, what if the rays would not go as a straight line, what if they would curve?

as far as i understand curved secondary ray would result curved shadows, distorted shadows. which might be nice. Lets have a look at pictures if that helps understand.

Of course we would want to curve our rays only very little to give a subtile feel to it :)

What if we could animate these curves light is being traced? what if we could make wind move the shadows themselves? non realistic? not at all, but might be an interesting visual effect?

any ides?

any ray tracing engine writers out there?

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ok, so i had this idea, and shared it whith people on cgtalk.

here are some very good replyes:

cignox1:

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Honestly, I don’t really see the point to implement something like this… of course, it may result in some nice effects. An implementation detail:

Since raytracers usually use the parametric ray formula (origin + direction) to represent rays, using curves would lead to a big change in current code. I can think to two ways to simplify this: the first is by approximating the curve with segments (the last of wich is used as a traditional ray). The second is by using a curve, but cutting it at the end by using a small straight line.

One aspect where this may be interesting is in physic: using appropriate curves you could build a raytracer that takes relativistic effects into consideration: when a ray approaches a massive object (i.e a star), the space distortion modifies the trajectory of the rays, wich becomes curve (in the 3d space). I think that someone did something similar a few years ago, by simulating how an observer would see the universe while falling in a black hole. They rendered a short movie, but I don’t remember who did that.

cignox1 is offline Report Bad Post Mark this post as useful

and

yarniso: (http://forums.cgsociety.org/member.php?u=90993)

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There have indeed been previous attempts to include relativity into ray tracing, providing some interesting results. Check for example:

http://www.hakenberg.de/diffgeo/special_relativity.htm

http://www.anu.edu.au/Physics/Searle/

http://www.fourmilab.ch/cship/cship.html

Enjoy

cignox1: (http://forums.cgsociety.org/member.php?u=209425)

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here a few other ones:

http://www.photon.at/~werner/Relativity.html

http://www.photon.at/~werner/black-earth/

http://casa.colorado.edu/~ajsh/schw.shtml

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so who ever is interested you can have a look at provided links.

i fuond interesting paper on a subject:

http://www.vis.uni-stuttgart.de/rel…ing/vis00gr.pdf

Abstract

In this paper, general relativistic ray tracing is presented as a tool for

gravitational physics. It is shown how standard three-dimensional

ray tracing can be extended to allow for general relativistic visualization.

This visualization technique provides images as seen by

an observer under the influence of a gravitational field and allows

to probe spacetime by null geodesics. Moreover, a technique is

proposed for visualizing the caustic surfaces generated by a gravitational

lens. The suitability of general relativistic ray tracing is

demonstrated by means of two examples, namely the visualization

of the rigidly rotating disk of dust and the warp drive metric.

The way I see it, this would be entirely possible. Right now rays are calculated as o + tv, a point and a direction. By changing this formula to something more general, it’s quite easy to do certain effects.

This is in fact one of the suggested ways to implement non-linear transformations on objects. In “An Introduction To Ray Tracing” there’s a short blurb on implementing operations such as a twist or bend as the inverse of such a thing on the ray.

The only real problem with this is that the intersection function becomes a lot more complicated to compute and so takes a lot longer. But if you’re willing to wait, this is a great solution (which isn’t too hard to implement) to getting mathematically perfect non-linear transformations.

So yes, by applying these transformations to shadow rays, you could end up with some fun-shaped shadows. Might even be fun to have a bit of randomness added with some soft shadows.

cool, thanks for support guillaumecl :)

Now all i have to do is to find some student who has no idea what to do for his computer graphicks final presentation/thesis/diploma

any ideas? :)

thanks for your thoghts.

m.