- Every time we process an ACK opcode, toggle page 1/page 2 soft
switches to steer subsequent writes between MAIN and AUX memory
- while I'm here, squeeze out some unnecessary operations from the
buffer management
On the player side, this is implemented by maintaining two screen
memory maps, and alternating between opcode streams for each of them.
This is using entirely the wrong colour model for errors, but
surprisingly it already works pretty well in practise (and the frame
rate is acceptable on test videos)
DHGR/HGR could be made runtime selectable by adding a header byte that
determines whether to set the DHGR soft switches before initiating
the decode loop.
While I'm in here, fix op_terminate to clear keyboard strobe before
waiting.
- can't emit Terminate opcode in the middle of the bytestream
- pad the TCP stream to next 2k boundary when emitting terminate opcode,
since the player will block until receiving this much data.
Clean up naming in edit_distance
In video encoder, when we emit additional offsets as part of an opcode,
reinsert back into the priority heapq if the new edit distance is
nonzero, in case we get the chance to fix it up later in the frame.
Also make sure to zero out the diff_weights and content_deltas
so we don't consider the offset again as a side-effect of some other
opcode.
Instead of prioritizing side-effect offsets by their previous update
priority, prioritize by those with the lowest (error - edit) delta i.e.
not introducing too much error relative to their edit distance.
