Used by the routine at DRAW_ROOM_RECORD.

One command of a room's (or a part's) drawing, at IX; on return IX is at its last byte, and the loop (DRAW_ROOM_RECORD) steps past it. The commands are laid out in the rooms' entries; this is what they do. The point is x, y at IY+$64, IY+$65 and the second point at IY+$66, IY+$67; y counts up from the bottom of the screen, and rows go modulo 192.

Points, $00-$BF: the byte is a row, the next a column, and the point moves there. With mode bit 4 the two are added to the point instead; bit 6 mirrors the column (255 less it, or negated when it is added); bit 3 moves the second point by as much as the point; bit 5 draws a line from the second point to the new point (MORE_ROOM_COMMANDS); and bit 2 then makes the new point the second point too, so that the next line starts where this one ended.

$C0, a row and a column: the second point, set, or with bit 4 moved, as a point is. $CF: the second point to the point. $D0: the two swapped. $D6: the end of a repeat started by $D5 (MORE_ROOM_COMMANDS): IY+$6C counted down, and back to just after the $D5 while it has not run out. $E6-$FF: a flood fill with a texture from the point (FILL_NEXT_SEED; the textures are 32 bytes each from TEXTURES -- not all of them patterns). Everything else goes on to MORE_ROOM_COMMANDS: lines, the mode bits, the repeat's start, parts, the clean copy, and $E4 and its sub-commands.

In object mode (mode bit 7, which $E4 $04 sets for the rest of the room), a code below $E4 is an object: its type and four bytes, made into an object record at the next free one (IY+$38) by PLACE_OBJECT; $E4 does nothing; and $E6 up are patches (PATCH_RECORDS), which set the room's floor, ceiling and walls (FIXED_RECORDS) from the table of patches (at offset 778 of TEMPLATES).