APA102 individually addressable LEDs

I'm not 100% sure what it's doing, but I'd say lookup tables are the way to go. Also allocating a new Uint16Array each time around the loop isn't great - it'd be faster as a normal array.

Even something like:

var gdimlookup = {
  15: function(i) {
            if (ma <390 && mi < 300) {
                this.gdim[i]=3;
                return 10.33;
            } else if (ma <700 && mi < 500) {
                this.gdim[i]=7;
                return 4.4;
            } else if (ma <1700 && mi < 1000) {
                this.gdim[i]=15;
                return 2.06;
            } 
        },
  ... 
};
// ...
        
        var f = gdimlookup[this.gdim[i]];
        var mult = f?f(i):1;

would help, as it's not having to parse a whole bunch of stuff each time around the loop.