Conway's Game of Life
is not in the target domain of the Diderot DSL, but it is a simple
program for demonstrating strand communication, a new feature relative
to previous examples. Strands are located in their domain according to a
special variable named pos, and strands can learn about nearby strands
via the sphere query. Strands have read-only access to the values of
other strands' variables as they were at the start of the iteration.
It would take two iterations for information to get from strand, to another,
and back.
Diderot's strand communication was primarily intended for running particle
systems, in which particles are moving around in some domain, dynamically
changing which other strands they interact with, and the program output is a
1-D sequence (or set) of values. In this example, strands do not move,
and do not change their interacting neighbors, and the output is a rectangular
array. The sphere query (to find strands within some radius) will always
return the same 8 neighbors.
This example also shows off the snapshot mechanism that can be used to
inspect the state of computation at each iteration, by saving the values of
the output variable(s) during execution. This is enabled by the --snapshot
option to the compiler:
diderotc --snapshot --exec life.diderot
This adds a new -s option to the ./life executable, which controls the
periodicity of snapshots being saved, i.e. -s 1 means save at every iteration,
-s 10 means save at every tenth iteration. The default -s 0 means that no
snapshots are saved.
We can run Life with one of the supplied initial patterns in the patterns
subdirectory, like the Gosper glider
gun (as well
as clean up any results from a previous run):
rm -f state*{nrrd,png}
./life -s 1 -l 200 -NN 80 -init patterns/gosperglidergun.nrrd
which generates many state-NNNN.nrrd files, one for each iteration, starting
with state-0000.nrrd to record initialization state before the first iteration.
We can use some unu to turn these into an image sequence:
unu join -i state-*.nrrd -a 2 |
unu quantize -b 8 |
unu resample -s x4 x4 = -k box -c cell |
unu dice -a 2 -ff state-%04d.png -o ./
These example programs are mainly to demonstrate Diderot, but
learning some unu is a possible side-effect. Type unu to get a list
of all unu commands, and type, for example, unu quantize or unu resample to get the usage info for those commands, to learn about how
they are being used above. Finally,
ImageMagick's convert can then make an animated GIF:
convert -delay 2 state*.png gosperglidergun.gif
The resulting gosperglidergun.gif shows the
expected pattern evolution.