Routines
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56908: Identify objects for current room
Used by the routines at 50218, 52913 and 53273.
Input
B Room number (from 60087)
HL Address pointer to start of room item data at 29551
C Object number in table at 29551 (starts at #1)
This routine uses the room object table at 29551 and has a dual function:
  • Upon room entry, the routine checks for any objects in the room (first byte of set = room number)
  • The routine can also identify an object's data set from its object number
Depending on which check is needed, the B or C register is set before this routine is called, with the other set to zero.
In either case, once the item data is found, its details & current 'state' are copied into the object data set buffer at 60293.
56908 LD A,(60292) Counter. Starts at 0.
56911 INC A Room/object numbers start from 1 so we need to immediately increment the counter for the first data set...
56912 LD (60292),A ...and re-store
56915 LD A,(HL) First byte of data set
56916 CP 255
56918 JR NZ,56925
56920 LD (60292),A We've reached the end of the list - set counter byte to 255...
56923 JR 57014 ...and jump straight to RET
There are data sets still to check:
56925 LD A,C Are we doing the check against an object number or a room number?
56926 CP 0
56928 JR NZ,56936 Run one of the next two checks depending on whether the B or the C register contains the value to check
ROOM NUMBER CHECK
56930 LD A,(HL) C register is 0 so it's a room number check. Get the first byte of the room object set (this is the room number of the object)
56931 CP B Current room number - is the object in this room?
56932 JR Z,56959 If so, we've found an object in the room so jump to next routine to deal with it
56934 JR 56942
OBJECT NUMBER CHECK
56936 LD A,(60292) As we know the object number (data set number), we just need to perform the check against the incremental counter to find its data
56939 CP C Check object number set against counter
56940 JR Z,56959 If we've found it, jump to the next routine to handle its data
Object not found in this set after one of the above checks. Skip forward to next data set.
Data sets vary in size, so this routine identifies the number of bytes that need skipping to get to the next set.
56942 LD DE,7 Jump forward to 8th byte in original data set
56945 ADD HL,DE
56946 LD A,(HL) Byte indicates number of additional 4 byte data sets this item has
56947 INC HL
56948 LD DE,4 4 bytes for each set to skip
56951 CP 0 Have we skipped all the additional 4-byte sets for this item?
56953 JR Z,56908 If so, go and check for the next object in the list
56955 ADD HL,DE Skip this 4-byte data set
56956 DEC A Decrement the data set counter
56957 JR 56951 ...Until they're all skipped.
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