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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."
That completely depends on your point of view.
__ Someday, but not this morning, I'll finally learn to use the preview button.
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.
... on the subject, from someone that doesn't have a vested interest in seeing real time ray tracing in games becoming a reality.
http://realtimecollisiondetection.net/blog/?p=38
I was a founder of one of the Midwest's first rendering farms back in 1993, a company that has now moved on to product design. Back then we had Pentium 60s (IIRC) with 64MB of RAM. A single frame of non-ray traced 3D Studio animation took an hour or more. We had probably 40 PCs that handled the rendering, and they'd chug along 20 hours a day spitting out literally seconds of video. I remember our first ray trace sample (can't recall the platform for the PC, though) and it took DAYS to render a single frame.
I do remember that someone found some shortcuts for raytracing, and I wonder if that shortcut is applicable to realtime rendering today. From what I recall, the shortcut was to do the raytracing backwards, from the surface to the light sources. The shortcut didn't take into account ALL reflections, but I remember that it worked wonders for transparent surfaces and simple light sources. I know we investigated this for our business, but at the time we also were considering leaving the industry since the competition was starting to ignite. We did leave a few months early, but it was a smart move on our part rather than continue to invest in ever-faster hardware.
Now, 15 years later, it's finally becoming a reality of sorts, or at least considered.
Many will say that raytracing is NOT important for real time gaming, but I disagree completely. I wrote up a theory on it back in the day on how real time raytracing WOULD add a new layer of intrigue, drama and playability to the gaming world.
First of all, real time raytracing means amazingly complex shadows and reflections. Imagine a gay where you could watch for enemies stealthily by monitoring shadows or reflections -- even shadows and reflections through glass, off of water, or other reflective/transparent materials. It definitely adds some playability and excitement, especially if you find locations that provide a target for those reflections and shadows.
In my opinion, raytracing is not just about visual quality but about adding something that is definitely missing. My biggest problem with gaming has been the lack of peripheral vision (even with wide aspect ratios and funky fisheye effects). If you hunt, you know how important peripheral vision is, combined with truly 3D sound and even atmospheric conditions. Raytracing can definitely aid in rendering atmospheric conditions better (imagine which player would be aided by the sun in the soft fog and who would be harmed by it). It can't overcome the peripheral loss, but by producing truer shadows and reflections, you can overcome some of the gaming negatives by watching for the details.
Of course, I also wrote that we'd likely never see true and complete raytracing in our lives. Maybe I'll be wrong, but "true and complete" raytracing is VERY VERY complicated. Even current non-real time raytracing engines don't account for every reflection, every shadow, every atmospheric condition and every change in movement. Sure, a truly infinite raytracer IS impossible, but I know that with more hardware assistance, it will get better.
My experience over the years was ALWAYS with static images that were raytraced. They looked great, but it wasn't until I experienced raytraced animations (high res, many reflective and transparent layers with multiple light sources and a sun-source) that I really saw the benefit and how it would aid in gaming.
The next step: a truly 3D immersive peripheral video system, maybe a curved paper-thin monitor?
My blog
Professer Philipp Slusallek of the University of Saarbruecken demonstrated a dedicated raytracer in 2005, using a 66 MHz Xilinx FPGA with about 6 million gates. The latest ATI and nVidia GPUs have 100 times as many transistors and run at 6-8 times the clock with hundreds of times the memory bandwidth. Raytracing is completely parallelizable, and scales up almost linearly with processors, so it's not at all unlikely that if those kinds of resources were applied to raytracing instead of vectorizing you'd be able to add a raytracer capable of rendering 60+ FPS at the level of detail of the very latest games into the transistor budget of the chips they're designing now without even noticing.
Here's a debate between Professer Slusallek and chief scientist David Kirk of nVidia: http://scarydevil.com/~peter/io/raytracing-vs-rasterization.html .
Here's the SIGGRAPH 2005 paper, on a prototype running at 66 MHz: http://www.cs.utah.edu/classes/cs7940-010-rajeev/sum06/papers/siggraph05.pdf
Here's their hardware page: http://graphics.cs.uni-sb.de/SaarCOR/
It's amusing to read this. This guy apparently works for Intel's "find ways to use more CPU time" department. Back when I was working on physics engines, I encountered that group.
Actually, the Holy Grail isn't real time ray tracing. It's real time radiosity. Ray-tracing works backwards from the viewpoint; radiosity works outward from the light sources. All the high-end 3D packages have radiosity renderers now. Here's a typical radiosity image. of a kitchen. Radiosity images are great for interiors, and architects now routinely use them for rendering buildings. Lighting effects work like they do in the real world. In a radiosity renderer, you don't have to add phony light sources to make up for the lack of diffuse lighting.
There's a subtle effect that appears in radiosity images but not ray-traced images. Look at the kitchen image and look for an inside corner. Notice the dark band at the inside corner. Look at an inside corner in the real world and you'll see that, too. Neither ray-tracing nor traditional rendering produces that effect, and it's a cue the human vision system uses to resolve corners. The dark band appears as the light bounces back and forth between the two corners, with more light absorbed on each bounce. Radiosity rendering is iterative; you render the image with the starting light sources, then re-render with each illuminated surface as a light source. Each rendering cycle improves the image, until, somewhere around 5 to 50 cycles, the bounced light has mostly been absorbed.
There are ways to precompute light maps from radiosity, then render in real time with an ordinary renderer, and those yield better-looking images of diffuse surfaces than ray-tracing would. Some games already do this. There's a demo of true real-time radiosity, but it doesn't have the "dark band in corners" effect, so it's not doing very many light bounces. Geometrics has a commercial real-time game rendering system.
Ray-tracing can get you "ooh, shiny thing", but radiosity can get to "is that real?"