Thursday, April 08, 2010

Ray Tracing is the Technology of the Future...

...and it always will be!

Seriously, first, let's be clear: my opinions do not matter! X-Plane is a small program in a large market (game/graphics hardware) and as I've said before, flight simulators are not the early adopters of new tech. So (and this is a huge relief to me) I can do my job without correctly predicting the future of computer graphics.

Keep that in mind as I mouth off regarding ray tracing - I'm just some guy throwing tomatoes from the balcony. X-Plane doesn't have skin in the game, and if I prove to be totally wrong, we'll write a ray tracer when the tech scales to be flight simulator ready, and you can point to this post and have a good laugh.

With that in mind, I don't see ray tracing as being particularly interesting for games. I could make arguments that rasterization* is significantly more effecient, and will keep moving the bar each time ray tracing catches up. I could argue that "tricks" like environment mapping, shadow mapping, deferred rendering, and SSAO have continued to move effects into the rasterization space that we would have thought to be ray-tracing-only. (Heck, ray tracing doesn't even do ambient occlusion particularly well unless you are willing to burn truly insane amounts of computing power.) I could argue that there is a networking effect: GPU vendors make rasterization faster because games use it, and games use it because the GPU makers have made it fast. That's a hard cycle to break with a totally different technology.

I don't really have the stature in the world of computer graphics to say such things. Fortunately John Carmack does. Read what he has to say. I think he's spot on in pointing out that rasterization has fundamental efficiencies over ray tracing, and ray tracing doesn't offer enough real usefulness to overcome the efficiency gap and the established media pipe-line.

The interview is from 2008; a few months ago Intel announced that first-generation Larrabee hardware wouldn't be video cards at all. For all effective purposes from a game/flight simulator perspective, they basically never shipped. So as you read Carmack's contents re: Intel, you can have a good chuckle that Intels claims have proven hollow due to the lack of actual hardware to run on.

I will be happy to be proven wrong by ray tracing, or any other awesome new technology. But I am by disposition skeptical until I see it running "for real", e.g. in a real game that competes with modern games written via rasterization. Recoding old games or showing tech demos doesn't convince me, because you can recode an old game even if your throughput is 1/20th of rasterization, and you can hide a lot of sins in a tech demo.

Heck, while I'm putting my foot in my mouth, here's another one: unlimited detail. Any time someone announces the death of the triangle, I become skeptical. And their claim of processing "unlimited point cloud data in real time" strikes me as an over-simplification. Perhaps they can create a smooth level of detail experience with excellent paging characteristics (which is great!) but the detail isn't unlimited. The data is limited by your input data source, your production system, the limits of your hardware, etc. Those are the same limits that a mesh LOD system has now. In other words, what they are doing may be significantly more efficient, but they haven't made the impossible possible.

That is my general complaint with most of the "anti-rasterization" claims - they assume that mesh/rasterization systems are coded by stupid people - and yet most of the interesting algorithms for rasterization, like shadow mapping and SSAO, are quite clever. Consider these images: saying that rasterization doesn't produce nice images while showing Half Life 2 (2004, for the X-Box 360) is like saying that cars are not fuel efficient because a 1963 Cadillac got 8 mpg. The infinite detail sample images show a lot of repeated geometry, something that renderers today already do very well, if that's what was desirable (which it isn't).

Finally, is in favor of sparse voxel octrees (SVOs). SVOs strike me as the most probable of the various non-mesh-rasterization ideas floating around, and an idea that might be useful for flight simulators in some cases. To me what makes SVOs practical (and in defense of the unlimited detail folks, their algorithm potentially does this too) is that it can be mix-and-matched with existing rasterization technology, so that you only pay for the new tech where it does you some good.

* Rasterization is the process of drawing on the screen by filling in the pixels covered by a triangle with some shading.


Rob said...

It would be pretty cool to see voxels used to render the world right-down to blades of grass in and around the airports.

krz said...

procedural textures that generate bitmaps in a depth that makes sense can be handy i think. if the hardware would allow fast displacement based on such maps flightsims could benefit a lot visually. but personally the visual aspect of games is quite unimportant for me these days. games lack alot more regarding AI and dynamic animations. these fields are much more important to the user experience

Rob said...

It would be nice to see lighting effects similar to the bloom effects in H.A.W.X in a future version of x-plane.

Benjamin Supnik said...

Rob - yes it would be cool.

But how would it be any cooler than seeing triangle meshes used to render the world right down to the blade of grass in and around the airport?

(Existing third party packages are getting VERY close to doing this now...)