Fast LED light pattern generation help

What I want to do is either output a 25 light pattern x 20

You could try this:

// make my pattern
pattern = new Uint24Array(25);
for (var i in pattern) 
  pattern[i] = E.HSBtoRGB(i*0.1,1,1) ; // or whatever you need for some RGB stuff

require("neopixel").write(pin, E.toUint8Array({data:pattern.buffer, count:20}));

// this may also work - but i'm not 100% sure:
require("neopixel").write(pin, {data:pattern.buffer, count:20});

Uint24Array isn't actually in the JS spec, but it's super helpful for neopixels as you can write R/G/B in one go.

As @MaBe mentioned you can also try compiled code when you're calculating what your 25 LED pattern should be.

Note that you could also do stuff like:

pattern = new Uint24Array(25);
rpattern = new Uint24Array(25);
// ...
rpattern.set(pattern);
rpattern.reverse();

E.toUint8Array({data:[pattern.buffer,rpattern.buffer], count:10})

So then it does the pattern, but flips and repeats it so even if you start with red and end with green, there's no harsh point at which it changes