P3 RGB pixel panel

That's a shame. I wonder how long the init part of shiftOut actually takes... My gut feeling is not long. Also jsvIterateCallback should be pretty speedy when it's given something that is a big flat array.

Does ESP32 have the ability to access GPIO directly via an address in memory? I notice that on STM32, shiftOut is able to use jshGetPinAddress to get an address it can write to really quickly. We could maybe do the same for ESP32?