Ray Tracing for Gaming Explored

Vigile brings us a follow-up to a discussion we had recently about efforts to make ray tracing a reality for video games. Daniel Pohl, a research scientist at Intel, takes us through the nuts and bolts of how ray tracing works, and he talks about how games such as Portal can benefit from this technology. Pohl also touches on the difficulty in mixing ray tracing with current methods of rendering. Quoting: "How will ray tracing for games hit the market? Many people expect it to be a smooth transition - raster only to raster plus ray tracing combined, transitioning to completely ray traced eventually. They think that in the early stages, most of the image would be still rasterized and ray tracing would be used sparingly, only in some small areas such as on a reflecting sphere. It is a nice thought and reflects what has happened so far in the development of graphics cards. The only problem is: Technically it makes no sense."

Comments

This isn't what we need in games

[Lurks]

I guess one has to state the obvious in that by moving to a process which is not implemented in silicon, as with current graphics cards, the work must necessarily be done in software. That means it runs on CPUs and that's something Intel is involved in where as when you look at the computational share of bringing a game to your senses right now, NVIDIA and ATI/AMD are far more likely to be providing the horsepower than Intel.

But really, even if this wasn't a vested interest case (and it may not be, no harm exploring it after all) - the fact remains that we don't actually need this for games. Graphics hardware has gone down an entirely different route whereby you write little shader programs which create surface visual effects on top of the bread and butter polygons and textures. This is a well established system by now and has a naturally compressive effect. It's like making all your visual effects procedural in nature rather than giving objects simple real-world textures and then doing a load of crazy maths to simulate reality. It works very well. Rememeber a lot of the time you want things to look fantastical and not ultra-realistic so lighting is some of the challenge.

Games aren't having a problem looking great. They're having a problem looking great and doing it fast enough and game developers are having a problem creating the content to fill these luscious realistic-looking worlds. That's actually what's more useful, really. Ways to aid game developers create content in parallel rather than throwing out the current rendering strategy adopted world wide by the games industry.

Now hear this

[suso]

I get tired of hearing this talk about real time ray tracing. They might be able to get basic ray tracing at 15 frames per second or more. But it won't matter, the quality won't be as good as some of the high quality images that you see that take hours to render. Sometimes days.

See, the two are incompatible because the purpose is different. With games, the idea is "How realistic can we make something look at a generated rate of 30 frames per second". But with photorealistic rendering the idea is "How realistic can we make something look, regardless of the time it takes to render one frame."

And as time goes on and processors become faster and faster, the status quo for what people want becomes higher. Things like radiosity, fluid simulations and more becomes more expected and less possible to do in real time. So don't ever count on games looking like those still images that take hours to make. Maybe they could make it look like the pictures from 15-20 years ago. But who cares about that? Real time game texturing already looks better than that.

Re:Now hear this

[IceCreamGuy]

from TFA:

At HD resolution we were able to achieve a frame rate of about 90 frames per second on a Dual-X5365 machine, utilizing all 8 cores of that system for rendering. The quote is referring to Quake 4. So they already can raytrace a semi-modern game at 90 FPS, and they have a graph that very clearly shows raytracing at a performance advantage as complexity increases. Just look at the damn graph (page three), the point where raster performance and raytracing performance intersect can't be more than a couple years off, and it's apparent that we may even have crossed that point already. Continue becoming tired of hearing about raytracing, the rest of us will sit patiently as the technology comes of age. Personally, I'm tired of hearing about this HD stuff, I mean, it's not like HD TVs will ever be mainstream, with their huge pricetags and short lifespans. Oh wait...

Re:Now hear this

[suso]

The quote is referring to Quake 4. So they already can raytrace a semi-modern game at 90 FPS, and they have a graph that very clearly shows raytracing at a performance advantage as complexity increases. Just look at the damn graph (page three),

I don't have to look at the damn graph to tell you that what people are going to want is this

And what they are going to get is this

And, they should just be happy with this (which, is pretty awesome)

My point is that real time photorealistic rendering will never catch up with what people expect from their games. It will always be behind. If all you want is mirrors, then find a faster way to implement them at the expense of a bit of quality.

Re:Now hear this

[The_Wilschon]

I think you still should look at (and understand) the damn graph. The point of the article was that if you want a given complexity of scene (which translates into quality of image), you only have to get a little bit more complex than current game scenes before current ray tracing techniques become faster than current raster techniques. Thus, ray tracing at 30 fps will look better than raster at 30 fps in the near future, perhaps already. Ray tracing is the quickest known route to better graphics quality at the same frame rate in games.

Yes, what can be produced will still be behind what people want or expect. But ray tracing will be less far behind than rasters in the near future.

All of this is according to TFA; I don't know much about this from a technical standpoint.

Re:Adaptive techniques: make or break

[morgan_greywolf]

Linux hackers are far better coders then most people who use Visual Studio Um, those two groups aren't mutually exclusive. Many of us *nix hackers also have day jobs that require us to use tools like Visual Studio. You make assumptions that aren't true.

in the player's best interests, natch

[Speare]

Daniel Pohl, a marketer at Intel

There, fixed that for you.

Raytracing the shiny first-intersection makes a lot of sense, even if it doesn't sell more CPUs. Sure, some day we will all have stunning holistic scene graphs that fit entirely within the pipeline cache of the processor, but it's not yet time for that.

Every change in developing a game engine requires changes in the entire toolset to deal with how to produce assets, how to fit within render time limit budgets, and how to model the scene graph and the logic graphs so that both are easily traversed and managed.

In the meantime, we have a pretty nice raster system right now, with a development strategy that provides for all those needs. You might not think that fullscale raytracing would upset this curve, but I'm not convinced. What do you do when a frame suddenly is taking more than 1/30sec to render, because the player is near a crystalline object and the ray depth is too high? How do you degrade the scene gracefully if your whole engine is built on raytracing? We've all played games where things like this were not handled well.

I contend that game AI is sometimes more advanced than academic AI because game developers are results-oriented and cut corners ruthlessly to achieve something that works well enough for a niche application. The same goes for game graphics: 33 milliseconds isn't enough to render complex scene graphs in an academically perfect and general way, it will require the same results-oriented corner-cutting to nudge the graphics beyond what anyone thought possible in 33ms. If that means using raytracing for a few key elements and ray-casting/z-buffering/fragment-shading the rest of the frame, game developers will do it.