Learning Challenge: ZX Spectrum machine code: Day 27

Day 27 and I'm playing more with the screen rendering. I'm going to need to re-read this though as there's a lot to unpack in this section. Nice bit through is there's some baked-in shortcuts in the ZX Spectrum for mapping screen memory that I remember reading in the ULA book. Seriously, this machine has some interesting quirks but also some amazing design decisions.