jsnow: > I have recently posted a haskell port of my ocaml raytracer, Glome: > > http://syn.cs.pdx.edu/~jsnow/glome/ > > It supports spheres and triangles as base primitives, and is able to > parse files in the NFF format used by the standard procedural database > (http://tog.acm.org/resources/SPD/). It uses a bounding interval > heirarchy acceleration structure, so it can render fairly complicated > scenes in a reasonable amount of time. Shadows and reflections are > supported, but not specular highlights or refraction. > > It's still slower than the ocaml version, but at least they're in the > same ballpark (and a good part of that difference may be inefficiencies > in my BIH traversal). I would welcome any advice on making it go faster > or use less memory. > > I compile the program with "ghc Glome.hs --make -fasm -O2 -threaded > -fglasgow-exts -funbox-strict-fields -fbang-patterns -fexcess-precision > -optc-ffast-math -optc-O2 -optc-mfpmath=sse -optc-msse2". (I assume the > -optc options don't do anything unless you compile via C.) > > Here are some of my current concerns: > > -Multi-core parallelism is working, but not as well as I'd expect: I get > about a 25% reduction in runtime on two cores rather than 50%. I split > the default screen size of 512x512 into 16 blocks, and run "parMap" on > those blocks with a function that turns the screen coordinates of that > block into a list of (x,y,r,g,b) tuples that get drawn as pixels to the > screen through OpenGL by the original thread. > > -Memory consumption is atrocious: 146 megs to render a scene that's a > 33k ascii file. Where does it all go? A heap profile reports the max > heap size at a rather more reasonable 500k or so. (My architecture is > 64 bit ubuntu on a dual-core amd.)
> -Collecting rendering stats is not easy without global variables. It > occurs to me that it would be neat if there were some sort of write-only > global variables that can be incremented by pure code but can only be > read from within monadic code; that would be sufficient to ensure that > the pure code wasn't affected by the values. The sorts of things I'm > looking for are the number of calls to "trace" per image, the number of > BIH branches traversed and ray/triangle and ray/sphere intersections per > pixel. (Disclaimer: I don't really fully understand monads, so I may > be oblivious to an obvious solution.) Use a Writer monad to log statistics? Maybe a State monad. > -Is there a fast way to cast between Float and Double? I'm using Float > currently, and the only reason is because that's what the OpenGL api > expects. I'd like to be able to use either representation, but the only > way to cast that I've found so far is "float_conv x = > fromRational(toRational x)", which is too slow. I'd try realToFrac, which should be pretty much optimised away. With doubles, ensure you use -fexcess-precision -- Don _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
