Real-Time Ray Tracing : Holy Grail or Fools' Errand?

Friday 12th October 2007, 10:10:00 AM, written by Dean Calver

With Intel making noise about acceleration of real-time ray tracing in recent months, especially where it concerns future hardware they're working on, DeanoC found himself a little puzzled as to why.

Pitting real-time Whitted RT vs traditional real-time rasterisation, Deano's article compares the two approaches to see where the pros and cons of each approach lie. Should we be hailing our future shiny ball overlords, or does recent RT chatter need a bit more to back it up?

Have a read and find out!

Discuss on the forums

Tagging

b3d ± deanoc, whitted, ray, tracing, rasterisation


Latest Thread Comments (247 total)
Posted by MfA on Sunday, 05-Jul-09 22:24:32 UTC
Interesting perhaps, common not ... interference just like say spectral divergence aren't a big priority for rendering.

Posted by T.B. on Sunday, 05-Jul-09 23:25:32 UTC
Quoting MfA
Interesting perhaps, common not.
Kinda depends on how you look at it. Refraction is a pure wave effect, based on the change of the speed of light in a medium and Huygens' principle(*). Of course, you would have to be mad to implement it that way.

Now that I think about it - and after checking my office - that's not a good counter example, as visible refraction is really not that common in real life. But neither are chrome spheres. ;)

Yes, I'm splitting hairs. Sorry about that. I think it's safe to say that we agree. :)

(* If I remember my physics lectures correctly)

Posted by Laa-Yosh on Monday, 06-Jul-09 00:01:16 UTC
Quoting TEXAN*
Imagine a Virtua Fighter 6 with the following effects in realtime @ 1080p 60FPS -

http://www.youtube.com/watch?v=5-VqSpU7INI&feature=PlayList&p=6B764D589FB15750&playnext=1&playnext_from=PL&index=16

You'll never be able approximate that with rasterization. Not now, not in 50 years.
1. The video is hideous.

2. What's so special about any effects here? we have videogames with better lighting already...

Posted by rpg.314 on Monday, 06-Jul-09 01:14:33 UTC
Quoting T.B.
Kinda depends on how you look at it. Refraction is a pure wave effect, based on the change of the speed of light in a medium and Huygens' principle(*). Of course, you would have to be mad to implement it that way.

Now that I think about it - and after checking my office - that's not a good counter example, as visible refraction is really not that common in real life. But neither are chrome spheres. ;)

Yes, I'm splitting hairs. Sorry about that. I think it's safe to say that we agree. :)

(* If I remember my physics lectures correctly)
Nah, refraction isn't a pure wave effect. Interference and diffraction are.

Posted by hoho on Monday, 06-Jul-09 08:58:43 UTC
Quoting TEXAN*
I'm talking about the behaviour of the lighting, shadows and self shadowing. It is exactly as it is in real life, you can't code that in. The best you can do is exactly what you see is todays games.
Too bad they didn't have real-world shadows there then. You know, the effects that global illumination and soft shadows try to accomplish?

The chip itself seems interesting though. I believe it's meant to trace beizer patches instead of triangle soup. I'm sure bigger car companies are very interested in a system that can render their car designs in real-time without having to preprocess them too much. Proper headlight simulations are also quite important for them.

Posted by Scali on Monday, 06-Jul-09 09:58:42 UTC
Quoting rpg.314
Nah, refraction isn't a pure wave effect. Interference and diffraction are.
What about refraction through a prism for example?
The 'rainbow' effect is a result of different wavelengths having different refraction angles, right?
But I agree that most raytracers don't bother to model light this way. They tend to model refraction the same way as reflection, which isn't correct.
This is generally a case where you use a photonmapping approach again. You can emit photons with various wavelenghts, and use the wavelength in calculation of the refraction angle.

Posted by T.B. on Monday, 06-Jul-09 18:51:13 UTC
Quoting rpg.314
Nah, refraction isn't a pure wave effect. Interference and diffraction are.
Yeah, back when I was a kid, interference was how we explained refraction. ;)
See this: http://en.wikipedia.org/wiki/Huygens%E2%80%93Fresnel_principle

Posted by rpg.314 on Monday, 06-Jul-09 19:12:53 UTC
Quoting Scali
What about refraction through a prism for example?
The 'rainbow' effect is a result of different wavelengths having different refraction angles, right?
Refraction can be explained using the particle model for light if you give your particles funny (somewhat) properties.

Posted by NeoTechni on Friday, 26-Mar-10 09:30:37 UTC
Quoting FromTheArticle
It's impossible to have a ray that partially intersects an object.
Why?

Couldn't you have the ray check the angle of whatever surface it hits, and if it's close to being parallel to the ray, then keep going to the next intersection, then combine the 2 colors using a weight based on how close to parallel the first object was?

Couldn't you check the adjacent "pixels" of where the ray hits, like super sampling? If the "pixel" wasn't on the same object then cast a new ray and again average all the colors?

(pixels in quotes cause it's probably the wrong term to be using, but close enough to what I'm trying to say)

Posted by MfA on Friday, 26-Mar-10 18:41:48 UTC
By definition, just like you can't have a point with an area. You can trace beams, but then it's not a ray.


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