A Blobby Language

As I don't want to run the risk of drawing down the ire of George Lucas's lawyers I work hard not to post anything in my blog that has anything to do with my work, that could be useful for work, or even anything that could have any useful application whatsoever. But earlier this year I presented a little bit of work publicly and the presentation is available online, so there can be no harm in linking to it.



First some background: Renderman is a "production quality" 3D renderer developed by Pixar and used by many visual effects houses, including my employer, ILM. One of its neatest features is that lighting and shading computations (ie. the calculation of the colour of every pixel once the geometry that you're looking at has been determined) are performed in a shading language called Renderman Shader Language. It's a C-like DSL that's compiled to a bytecode that runs on a SIMD virtual machine.

Buried within the Renderman documentation is another less well known virtual machine that is used to compute "blobbies". A blobby is simply an isosurface, ie. the set of points that form the solution to f(x,y,z)=c for a function f. The virtual machine is the one on which the function f is computed. Unlike shading, however, there are bytecodes for this VM, but no programming language. So this presentation was about my solution to the problem: embedding a tiny DSL in Python that compiles down to bytecodes. You write ordinary looking Python code but arithmetic operators and other functions are overloaded to build an AST that is converted to an "opcode" stream that is sent to Renderman. From a computer science standpoint it really is basic stuff, but as the author of the blobby code (Tom Duff of Duff's Device in fact) said to me, he's been waiting for someone to write a compiler for his opcodes for years and mine was apparently the first one. So here's a link to the presentation. There isn't really much detail in the presentation, but it might give at least a tiny flavour of what I do in my day job.