gallery/noise: Initial commit

[rawiriblundell]

Hi there,
I've thrown together this screensaver based loosely off the existing stars screensaver.

A few comments: We reduce a couple of potentially unnecessary external calls by using built-in vars, with external-call-fallbacks like so:

# Get terminal dimensions
width="${COLUMNS:-$(tput cols)}"
height="${LINES:-$(tput lines)}"

This gets the state that the script was launched within, but does not work reliably with SIGWINCH. SIGWINCH should be rare anyway, we just eat the cost of a couple of tput calls.

(Noting that tput itself isn't 100% portable, but that only matters if you're running something like OpenBSD.)

We also lean on SRANDOM when it's available (bash 5.1+) and fall back to RANDOM when it's not. I doubt there's any practical or appreciable difference, but logically we're pulling from the system entropy pool rather than bash's croaky old LCG RNG, so that should scale better. Hypothetically. Maybe.

I initially had several selectable colour sets, but the addition of shading blocks enabled that to be compacted down. Now it has two sets: greyscale or greyscale with some red, green, blue and yellow codes thrown in.

I use a slightly debiased modulo approach to provide a fair random selection between the two colour sets. Here I just use RANDOM because SRANDOM is a sledgehammer for a one-off coin-toss.

Tested on bash 4 and 5 on Linux. I don't have a Mac available to me, but I don't see anything that would upset bash 3.

Thanks!