A map stream is a run of Entity::MakeMessage records. Each
carries its own length at +0, its class at +28, the resource it names at +40, its
instance flags at +44 and its origin at +48 — and BT pads each record to the
next four bytes, which Red Planet does not. The resource named is a Model List;
the outline the display draws is the GaugeImage inside that list, so the join is direct
rather than by name. A model with no GaugeImage is not drawn, which is why several
streams place far more than they draw.
Colours are palette indices resolved through btspal.pcc, the
palette L4GAUGE.CFG configures the secondary port with:
configure(0,sec,270,0x003F,clut0,rgb,btspal.pcc). Unlike Red Planet,
every primitive here carries an explicit colour — nothing falls back to a display
default. Seen from above, +X runs right and +Z up.
Two of the eight playable maps, arena1 and
arena2, place almost nothing: a sky and a pair of records too short to
carry an origin. Their arena geometry is arenall, which is a stream of its
own. adrop and pol4sfx are likewise supporting streams
— drop points and wind emitters — rather than places you fight in.