DIY Gamer Conversion

It'll be because SPI outputs most significant bit first. It'd be easy enough to change updateDisplay to flip that around.

I'd also consider replacing currentRow with 1<<counter (or 128>>counter if it's backwards). You can then remove the currentRow variable.

I don't think you'll get much extra by decreasing setInterval past 1 - in fact if you're telling it to go faster than it wants to, it might adversely impact rendering of other stuff.

The hardware's a bit of a strange setup to be honest. It feels like a MAX7219 would have been way better (and would have only required a single chip to be soldered).