PowerVR GR6500: Ray tracing is the future and the future is now • Hacker News Board

Re: PowerVR GR6500: Ray tracing is the future and the future is now

#31

Post by gfodor » Wed, Mar 19, 2014, 12:52 AM UTC

duaneb wrote: post #22

tinco wrote: post #16

Earlier quoted context omitted.

I'm sorry man, but that sounds crazy. Raytraced scenes are much easier for artists to control the results because things actually behave like you would intuitively expect (if the amount of rays is high enough). If raytraced scenes were hard to control, why would every single animated movie be raytraced? Raytracing really is the be all and end all of graphics. The more rays you can render, the more realistic your scen…

Raytracing is just one tool in a bag of necessary algorithms. For instance, there's no obvious way to extend raytracing to offer indirect lighting—all existing algorithms offer some form of tradeoff. Furthermore, many effects are flat out a pain to render with raytracing: displacement mapping, subsurface scattering, anti-aliasing, and scenes where both speed of rendering and dynamic geometry are needed. All of those…

Uh, what. Sampled raytracing is the most natural approach to indirect lighting, displacement mapping, subsurface scattering, and anti-aliasing.

As far as non-realistic rendering goes I am not sure how this is relevant, you can alter the properties of light and still use ray tracing, and many effects use image based techniques anyway.

Raster will die in the long run, it's pretty obvious.

Re: PowerVR GR6500: Ray tracing is the future and the future is now

#32

Post by joesmo » Wed, Mar 19, 2014, 12:52 AM UTC

fidotron wrote: post #3

It's best to remember that ray tracing isn't the be all and end all of graphics since it's far harder for artists to control the results than the other hacked up ways. One consequence of this is their example comparison, where I think it's entirely subjective to say the ray traced output is better. Neither is particularly great. The big win is around indirect lighting, but the development of that in standard rasteris…

I don't think so, not with modern tools anyway. Raytracing is in my experience the technology that most closely models the real world. Most technologies used in games even today are hacks, using precomputed values oftentimes derived from ray traced models. Raytracing is quite natural to work with because it simulates real world objects and does so in a realistic manner. The only difficulty might be caused by the lack of such real-time raytracing hardware as depicted here causing slower development as one has to wait for a scene or animation to render. IMO, raytracing is indeed the pinnacle of photorealistic rendering currently.

Re: PowerVR GR6500: Ray tracing is the future and the future is now

#33

Post by subb » Wed, Mar 19, 2014, 1:00 AM UTC

duaneb wrote: post #22

tinco wrote: post #16

Earlier quoted context omitted.

I'm sorry man, but that sounds crazy. Raytraced scenes are much easier for artists to control the results because things actually behave like you would intuitively expect (if the amount of rays is high enough). If raytraced scenes were hard to control, why would every single animated movie be raytraced? Raytracing really is the be all and end all of graphics. The more rays you can render, the more realistic your scen…

Raytracing is just one tool in a bag of necessary algorithms. For instance, there's no obvious way to extend raytracing to offer indirect lighting—all existing algorithms offer some form of tradeoff. Furthermore, many effects are flat out a pain to render with raytracing: displacement mapping, subsurface scattering, anti-aliasing, and scenes where both speed of rendering and dynamic geometry are needed. All of those…

Path tracing can be seen as a extension of ray tracing that supports a much broader range of effect like indirect lighting, soft shadows, anti-aliasing, etc. With the correct function for the material, you can simulate subsurface scattering relatively easily too. But, to me, the beauty of this technique goes beyond the effects you can achieve: it's an incredibly compact, uniform way of simulating light. Compared to rasterization, which to get the same result, you need a enormous code base that deals with very effect with caution. Adding a reflection in a rasterized scene might not reflect your shadows, etc. You need care about every possible interaction between every effect.

Re: PowerVR GR6500: Ray tracing is the future and the future is now

#34

Post by gfodor » Wed, Mar 19, 2014, 1:08 AM UTC

InclinedPlane wrote: post #12

higherpurpose wrote: post #6

What's the difference between ray tracing and path tracing? And could we have a path tracing chip? This demo was pretty impressive. I think they said they used 4 Titans at 720p. https://www.youtube.com/watch?v=aKqxonOrl4Q

Ray tracing works backwards from the way actual optics works. It sends out a ray for each pixel and then finds out what it falls on then does math to figure out what it should look like. In a simple example, you have a few light sources and you trace a ray back to an object (polygonal surface), then you shoot off other rays from there toward the light sources (or you shoot off potential reverse reflection rays). If s…

This sounds somewhat wrong. Ray tracing is just another term for path tracing, as paths are made up of traced rays. A naive camera-to-light witting ray tracer is still a sampling path tracer but has bias towards a specific subset of paths, namely those which follow specular bounces from the eye to the light or those which have one diffuse bounce.

Much of the progress in photorealistic rendering has come from improving the techniques used to sample paths. Bi-directional path tracing samples paths by tracing paths from both the light and the eye and performing a technique called multi-importance sampling in order to weight them appropriately. This allows the algorithm to pick up more light paths that would otherwise be hard to reach, such as those which form caustic reflections.

One of the more recent developments on this front is the use of the "specular manifold", which allows a path sampler to "walk" in path-space that allows capturing of even more partially-specular paths. (See Wenzel 2013.) This technique allows efficient sampling of the main light transport paths in scenes where a specular transparent surface surrounds a light source, ex a light bulb casing.

Edit: for this specific hardware, it sounds like they are using a hybrid approach so may very well be doing a basic eye-to-light ray tracing algorithm and then using raster for diffuse surface shading.

Re: PowerVR GR6500: Ray tracing is the future and the future is now

#35

Post by eigenbom » Wed, Mar 19, 2014, 1:10 AM UTC

I'd wager that the current rasterising pipeline is more flexible than one based on raytracing - capable of generating a range of styles, not just photorealistic ones. And therefore having an extra dedicated chip for raytracing seems uneconomical.

The comparison examples given in the article were slightly ridiculous. How does a non-reflective car represents 'traditional' rendering? Look at any great AAA game and you'll see reflections, refractions, radiosity, etc., that are all pretty amazing. I don't think that general demand will be there for alternative rendering hardware for quite a while.

Re: PowerVR GR6500: Ray tracing is the future and the future is now

#36

Post by banachtarski » Wed, Mar 19, 2014, 1:22 AM UTC

eigenbom wrote: post #35

I'd wager that the current rasterising pipeline is more flexible than one based on raytracing - capable of generating a range of styles, not just photorealistic ones. And therefore having an extra dedicated chip for raytracing seems uneconomical. The comparison examples given in the article were slightly ridiculous. How does a non-reflective car represents 'traditional' rendering? Look at any great AAA game and you'l…

Those reflections and refractions and such rely on raytracing though so better ray-tracing hardware will help improve traditional pipelines as well (which are increasingly getting physically based).

Also, there is nothing intrinsic about the rasterization pipeline that makes it more or less flexible that a ray-tracing one. In a physically based engine, I'd imagine you would be able to inject shader code on every bounce (for bump mapping, BRDF behavior, subsurface scattering, etc) as well as when the ray hits the lens. A good system would allow you to spawn more rays as need be or modify geometry like the current tesselation and geometry shaders.

I think the important thing is that a physically based model would be amazing to work with from a graphics engineer perspective. No more crazy floating point hacks or occlusion tricks to get the desired effect. I'd rather the hacks be at the hardware level than the software level.

Re: PowerVR GR6500: Ray tracing is the future and the future is now

#37

Post by banachtarski » Wed, Mar 19, 2014, 1:24 AM UTC

fidotron wrote: post #3

It's best to remember that ray tracing isn't the be all and end all of graphics since it's far harder for artists to control the results than the other hacked up ways. One consequence of this is their example comparison, where I think it's entirely subjective to say the ray traced output is better. Neither is particularly great. The big win is around indirect lighting, but the development of that in standard rasteris…

Imagine you were an artist trying to light an indoor room. Would you rather have to place hundreds of small lights everywhere and experiment for days or weeks to get the correct ambient glow? Or would you rather stick a big sun outside and call it quits?

There's a reason Pixar is using physically based lighting to construct all their scenes.

Re: PowerVR GR6500: Ray tracing is the future and the future is now

#38

Post by pjackson5 » Wed, Mar 19, 2014, 1:31 AM UTC

chrisseaton wrote: post #29

tinco wrote: post #16

Earlier quoted context omitted.

I'm sorry man, but that sounds crazy. Raytraced scenes are much easier for artists to control the results because things actually behave like you would intuitively expect (if the amount of rays is high enough). If raytraced scenes were hard to control, why would every single animated movie be raytraced? Raytracing really is the be all and end all of graphics. The more rays you can render, the more realistic your scen…

"If raytraced scenes were hard to control, why would every single animated movie be ray traced?" I'm not entirely sure that's actually true. In this paper ( http://graphics.pixar.com/library/RayTracingCars/paper.pdf ) Pixar talk about how the first movie they even tested using ray tracing on was Cars. Before that they were using scanline rendering.

I think you are missing a shift that has happened in the industry over the last few years. Yes, now that computers are fast enough, pixar raytraces everything in renderman. Most other major studios use that or arnold, a pure raytracer.

Re: PowerVR GR6500: Ray tracing is the future and the future is now

#39

Post by lcrs » Wed, Mar 19, 2014, 1:32 AM UTC

gfodor wrote: post #31

duaneb wrote: post #22

Earlier quoted context omitted.

Raytracing is just one tool in a bag of necessary algorithms. For instance, there's no obvious way to extend raytracing to offer indirect lighting—all existing algorithms offer some form of tradeoff. Furthermore, many effects are flat out a pain to render with raytracing: displacement mapping, subsurface scattering, anti-aliasing, and scenes where both speed of rendering and dynamic geometry are needed. All of those…

Uh, what. Sampled raytracing is the most natural approach to indirect lighting, displacement mapping, subsurface scattering, and anti-aliasing. As far as non-realistic rendering goes I am not sure how this is relevant, you can alter the properties of light and still use ray tracing, and many effects use image based techniques anyway. Raster will die in the long run, it's pretty obvious.

Raytracing may be conceptually the most natural but it's not always the best choice for a lot of these cases - displacement, motion blur, depth of field and anti-aliasing are still often handled much more quickly by micropolygon/scanline rendering even if the lighting and shading is raytraced. Hair and fur is pretty problematic with raytracing too.

That said, physically-based shading is massively easier to art-direct, even if the "front end" as it were of the renderer isn't naively tracing rays from the camera. There's a killer set of slides and notes documenting ILM and Sony's switch to PBR here: http://renderwonk.com/publications/s2010-shading-course/

Re: PowerVR GR6500: Ray tracing is the future and the future is now

#40

Post by doktrin » Wed, Mar 19, 2014, 1:40 AM UTC

tinco wrote: post #16

fidotron wrote: post #3

It's best to remember that ray tracing isn't the be all and end all of graphics since it's far harder for artists to control the results than the other hacked up ways. One consequence of this is their example comparison, where I think it's entirely subjective to say the ray traced output is better. Neither is particularly great. The big win is around indirect lighting, but the development of that in standard rasteris…

I'm sorry man, but that sounds crazy. Raytraced scenes are much easier for artists to control the results because things actually behave like you would intuitively expect (if the amount of rays is high enough). If raytraced scenes were hard to control, why would every single animated movie be raytraced? Raytracing really is the be all and end all of graphics. The more rays you can render, the more realistic your scen…

> If raytraced scenes were hard to control, why would every single animated movie be raytraced?

That's a bit of a stretch. Pixar didn't use ray-tracing until Cars [2006]. Even then, it was only applied for secondary effects.

It wasn't until Monsters University [2013] that they produced the majority of a movie using ray-tracing [1]. That's a recent development, IMHO.

[1] http://thisanimatedlife.blogspot.com/2013/05/pixars-chris-ho...