P3 RGB pixel panel

Wow, that stumped me - then I found:

function tstLedShiftOut(cnt){
  var arr = new Uint8Array(1024);
  var sfnc = shiftOut.bind(null,[pin,pin,pin,pin,pin,pin],{clk:pin});
  for(var i = 0; i < cnt; i++){
    sfnc(new Uint8Array(arr,i*64,64));
  }
}
function tstLedShiftOut2(cnt){
  var arr = new Uint8Array(1024).buffer;
  var sfnc = shiftOut.bind(null,[pin,pin,pin,pin,pin,pin],{clk:pin});
  for(var i = 0; i < cnt; i++){
    sfnc(new Uint8Array(arr,i*64,64));
  }
}
test("tstLedShiftOut(16)");
test("tstLedShiftOut2(16)");

> LedShiftOut(16) : 473
> LedShiftOut2(16) : 13

The Array copy does take a bunch of time - but if you use .buffer then it's not doing a copy - it just creates a 'view' and no data gets allocated or shovelled around.

That might well sort out your ESP32 issues :)