Routines
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9FF8: Describe the doors of a room
For each exit of room A that has a visible door, prints 'to the east there is the round green door' (or 'above'/'below' for up and down).
9FF8 PUSH BC Save the caller's BC, DE, IY and IX
9FF9 PUSH DE
9FFA PUSH IY
9FFC PUSH IX
9FFE CALL $9FDE IX = the start of room A's exits, BC = 3 (the size of each one)
A001 ADD IX,BC Step back one exit's width, so the loop below lands on the very first exit the first time round
A003 PUSH IX IY will be the loop's own pointer, a copy of IX
A005 POP IY
A007 SUB A Is this the very first exit (guards against a room with no exits at all)?
A008 CP (IY+$01)
A00B JR Z,$A043 It is: there is nothing to describe yet, so skip straight to moving on
A00D LD A,(IY+$01) A = this exit's door object
A010 CALL $9B25 IX = the door's own record
A013 BIT 7,(IX+$07) Is the door visible?
A017 JR Z,$A043 No: say nothing about it and move on
A019 LD DE,$0008 DE = 8: the offset, from the start of a record, to an object's own words
A01C ADD IX,DE IX = the door's own words
A01E PUSH IX Save that for a moment
A020 LD A,(IY+$00) A = this exit's direction
A023 CALL $9FEA DE = the word for that direction
A026 CP $09 Is the direction UP or DOWN (9 or 10)?
A028 JR C,$A034 No: use the ordinary "to the <direction> there is" wording
A02A LD DE,$07B9 "above"
A02D JR Z,$A03A It was UP: use that word
A02F LD DE,$082F "below"
A032 JR $A03A It was DOWN: use that word instead
A034 LD HL,$AD0A "to the <direction> there is"
A037 CALL $72D4
A03A CALL $74B8 Print the direction word (or "above"/"below")
A03D LD HL,$AF05 "the <door>."
A040 CALL $72D4 Print it, naming the door
A043 ADD IY,BC Move on to the next exit
A045 LD A,$FF Have we reached the end of the exits?
A047 CP (IY+$00)
A04A JP NZ,$A007 Not yet: look at this next one
A04D POP IX Finished: restore the caller's IX, IY, DE and BC
A04F POP IY
A051 POP DE
A052 POP BC
A053 RET
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