Avalon: Routine at 49632

The next series of routines handle the graphics set-up for the door frames and doors in the room.

The following routine determines whether the items (doors and frames) being dealt with are on the back, right or left wall, and sets the A register (shortly to be stored at 60287) to 0, 1 or 2 respectively.

The incremental counter (60285) is checked against the first room data byte, which indicates the room size .

If the counter's value is 1 or 2, we're dealing with frames and doors on the left wall.
If its value is one of its final two checks (room size - counter <= 2) it's on the right wall.
Anywhere in between these two options, we're dealing with the back wall.

Used by the routine at 49858.
Identify and set up (mirroring if required, and storing address pointers) for each room element. Includes fixed scenery items such as wall/floor connectors and door frames. See Trivia: Setting the scene(ry) for information about how the room scenery is stored.
49632	LD A,(60285)	Room setup counter (to be compared with room size data byte at 49858)
49635	DEC A	The counter was pre-incremented in the earlier routine, so check its original value
49636	AND 3
49638	CP 0
49640	JR NZ,49653	Door and brickwork data that make up the room are stored in pairs of bits, so 4 to a byte. After evaluating 4 pairs, the data byte is dealt with, so can be advanced to the next byte in the room data set (at 25001). So skip the next instructions (that advance the pointer to the next room data byte) if original counter byte (before INC) is 1,2,3 - 5,6,7 - 9,10,11 etc. (not a multiple of 4)
Get room data byte from 25001 and advance room data address pointer, as we've dealt with the current byte
49642	LD HL,(60282)	Get room data address pointer
49645	LD A,(HL)	Get next room data byte
49646	INC HL	Increment address pointer to next byte
49647	LD (60282),HL	...and re-store address pointer
49650	LD (60286),A	Store room data byte
The next series of routines handle the graphics set-up for the door frames and doors in the room. The following routine determines whether the items (doors and frames) being dealt with are on the back, right or left wall, and sets the A register (shortly to be stored at 60287) to 0, 1 or 2 respectively. The incremental counter (60285) is checked against the first room data byte, which indicates the room size . If the counter's value is 1 or 2, we're dealing with frames and doors on the left wall. If its value is one of its final two checks (room size - counter <= 2) it's on the right wall. Anywhere in between these two options, we're dealing with the back wall.
49653	LD A,(60285)	Incremental counter, which is checked against with 1st byte from the room data set (in the table at 25001) which indicates the room size
49656	CP 3
49658	JR NC,49664
49660	LD A,2	If the counter byte is < 3, we're looking at LEFT wall items - set A to 2, for storing at 60287 shortly
49662	JR 49679
49664	LD C,A	If the counter byte is >=3 it could be the back or right wall
49665	LD A,(60284)	...Subtract it from the room data byte
49668	SUB C
49669	CP 2
49671	JR NC,49677
49673	LD A,1	If it's 0 or 1, the counter byte is on one of its last two values, so we're looking at the RIGHT wall - Set A to 1, for storing at 60287 shortly
49675	JR 49679
49677	LD A,0	If it's 2 or more, the counter byte is in between, so we're looking at the BACK wall - set A to 0, for storing at 60287 shortly