things to try:

* patch the entire expanded-ram imul8xe on top of imul8 to avoid the 3-cycle thunk penalty :D

* try 3.13 fixed point instead of 4.12 for more precision
  * can we get away without the extra bit?

* y-axis mirror optimization

* 'wide pixels' 2x and 4x for a fuller initial image in the tiered rendering
  * maybe redo tiering to just 4x4, 2x2, 1x1?

* extract viewport for display & re-input via keyboard

* fujinet screenshot/viewport uploader