iOS上使用C或ObjC进行实时raytracer吗？

Question

I'm starting to build a real-time raytracer for iOS. I'm new to this raytracing thing, all I've done so far is write a rudimentary one in ObjC. It seems to me that a C-based raytracer is going to be faster than one written in ObjC, but the ObjC one will be far simpler, as object hierarchies come in very handy. Speed is very important, though, as I want it to be real-time, say 30 fps.

What's your opinion on whether the speed up of C be worth the extra complexity? I can forsee the C code taking much longer and causing me headaches with lots of bugs (although I'm not new to C), but going for more speed is seductive initially.

Are there any examples out there of raytracers written in C? My google search for such things is contaminated with lots of results for C++ and C#.

Answer 1

If you want fast ray tracing, you can pretty much forget about using either C or Objective C. You almost certainly want to use OpenCL. It's still not going to be enough to get you (even very close to) 30 fps, but it'll probably be at least twice as fast as anything running on the CPU (and 5-10 times faster wouldn't be any real surprise).

Answer 2

as zneak stated, c++ is the best combination for speed and polymorphism.

however, you can accomplish something close by reducing the objc calls (read: reduce the polymorphic interface to the minimum set required, then just putting the parts that need to be fast in plain c or c++).

objc message dispatch is quite fast, and you can typically remove much of the virtual/dynamic methods from your interfaces (assume every objc instance method is virtual). c code in objc methods is still c code... from there, determine where your bottlenecks are -- it doesn't hurt to profile before changing working code, either ;)

Answer 3

Writing a "realtime Raytracer" is without the use of Hand-Optimized Assembly (or the use of the "cheap" Intel compiler ;) , but this is not possible for this platform), impossible because you need the speed.

Further more you need a lot of Processing power but i guess even the OpenCL path is not powerful enought (this is in my opinion the case even for real Desktop machines, the reason for this is the lack of an real big cache on the Graphics Processor).

Answer 4

Have a look through http://ofps.oreilly.com/titles/9780596804824/ that is as close as you'll get.

It isn't ray tracing, I have written a ray tracer and it is a huge amount of work. GL uses a different technique for graphics, hence it will be unable for example to render the capacity of a diamond to capture light. that link contains sample code, you can download and run it. You will realise that even some of the moderately complex examples really chug on an actual device... we are talking < 1 fps.