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28736: Open or close a door or window
Used by the routines at 28855, 28877 and 29681. On entry, A holds the door/window identifier:
ID Door/window
1 Left study door
2 Right study door
4 Science Lab storeroom door
8 Boys' skool door
16 Skool gate
32 Drinks cabinet door
64 Top floor window
128 Middle floor window
A Door/window identifier (see table above)
B 0 (close it) or 1 (open it)
28736 PUSH HL
28737 LD HL,32756 32756 holds the doors flags
28740 LD C,A Copy the door identifier to C
28741 LD A,(HL) Pick up the doors flags in A
28742 OR C
28743 DEC B Are we opening the door/window?
28744 JR Z,28747 Jump if so
28746 XOR C
28747 LD (HL),A Restore the doors flags with the appropriate bit set or reset
28748 LD A,C A=door identifier
28749 LD HL,57685 Point HL at the appropriate entry in the doors and windows table at 57686
28752 INC L
28753 INC L
28754 RRCA
28755 JR NC,28752
28757 LD A,(HL) Pick up the MSB of the entry in A
28758 ADC A,B Add 1 if opening the door/window
28759 DEC L Point HL at the LSB of the entry
28760 LD L,(HL) Pick this up in L
28761 LD H,A Now HL=address from the doors and windows table (+256 if opening)
28762 CALL 27672 Alter UDG references in the play area and update the SRB for the newly opened or closed door/window
28765 POP HL
28766 RET
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