Yeah, that's why FPGAs typically drive the matrix of dumb LEDs. But if you use APA102s, they remember their PWM setting, and a little chip inside each LED hand

Yeah, that's why FPGAs typically drive the matrix of dumb LEDs. But if you use APA102s, they remember their PWM setting, and a little chip inside each LED handles that. You just burst the data out over SPI, and the LEDs remain lit until you inform them of a new color to display. Expensive, but easy to use!