D benchmark code review

[logicchains]

I've posted a couple of benchmarks involving D previously and 
received complaints that the D implementation was ugly and 
un-idiomatic, so I thought I'd seek code review before posting 
the next one. The code is at 
https://github.com/logicchains/ParticleBench/blob/master/D.d; 
it's an OpenGL particle animation, and my D code is essentially 
just a direct port of the C implementation. Note however that, as 
the animation is gpu-bound, there's not much scope for 
optimisation of the code (in hindsight, it was a pretty poor 
topic for a benchmark, but hindsight always sees farthest and 
whatnot).