A weekend past and some new updates:
* The raytracer is now parallelized.
* I have found a parallel RNG scheme that allows reproducible multithreaded
result for those who wants to do parallel reproducible Monte-Carlo simulations:
* writeup
[https://github.com/mratsim/weave/issues/147#issuecomment-633198832](https://github.com/mratsim/weave/issues/147#issuecomment-633198832)
* the magic:
[https://github.com/mratsim/trace-of-radiance/blob/26ef9ed5/trace_of_radiance/support/rng.nim#L21-L29](https://github.com/mratsim/trace-of-radiance/blob/26ef9ed5/trace_of_radiance/support/rng.nim#L21-L29)
a `pair` function that can take 2 integers (for example one produced by a
"master RNG" and one from a loop variable, or 2 from nested loop variables) and
that can be used to reseed RNGs across threads to:
* ensure different RNG streams
* ensure reproducibility
* I departed a bit from the book to add an animation:
* For this I have added:
* a mini physics engine that can simulate gravity and bounce
* the output can now be a series of PPM images
* the output can be a mp4 video in H.264 format
* The H264 encoder is lossless and less than 300 lines of pure Nim:
*
[https://github.com/mratsim/trace-of-radiance/blob/26ef9ed5/trace_of_radiance/io/h264.nim](https://github.com/mratsim/trace-of-radiance/blob/26ef9ed5/trace_of_radiance/io/h264.nim)
* When passed to FFMPEG, it will complain about corrupted frames but
ssshhhh, don't let it say otherwise, it's spec compliant and can be read by
media players ;)
* I've added a MP4 muxer (this one is full-featured via the minimp4
header-only library)
* color conversion for RGB to Y'CbCr 420 (also known as YUV420 i.e. with
chroma subsampling).
Limitations:
* It's very very slow, ~3 hours of rendering on 18 cores for a 576x324 image
with 400+ spheres and 300 rays per pixels. The reason why is that each ray must
test if it encounters any of the sphere, and redo that after each bounce, a ray
can bounce up to 50 times (artificial limit otherwise compute never finishes).
* Solution is in the volume 2 "Raytracing the next week", via Bounding
Volume Hierarchy (BVH), which will make the time needed logarithmic (and
assuming 10000 seconds of initial rendering time ln(10000) == 9)
* No Motion blur, I added animation but no motion blur.
* Solution is in the volume 2 "Raytracing the next week", as well. But the
book simulates motion blur but has no animation code ;).
Note: Feel free to reuse the video code to record the NimConf but 6 seconds of
size 576x324 took 53MB ;)
