Avalon: Routine at C15A

C15A: Room initialization - identify room data set and scenery style, reset room/viewport position


Find the current's room data set in the table at 61A9:
C15A	LD HL,($DAF7)	Pointer to series of room data sets at 61A9.
C15D	LD A,($EAB7)	Get room number
C160	LD C,A	Store in C register
C161	LD B,$01	Set incremental compare counter to compare room number against
Identify data set for current room from list at 61A9
C163	LD A,C
C164	CP B
C165	JR Z,$C170	If room data byte (A) = counter (B), we're at the right place, so skip out of the loop
Not this set. Move to the end of the set (set length will vary)
C167	LD A,(HL)	Get byte of room data set
C168	INC HL	Increment it
C169	CP $FF	Are we at an end-of-data-set marker?
C16B	JR NZ,$C167	Continue till we are
C16D	INC B	We're at the end of this set. Increment the counter
C16E	JR $C163	Keep comparing until we're at the right place for the room
Data set for current room identified
C170	LD ($EB7A),HL	Store address pointer for current room data bank.
Check if the room is a vertical tunnel
C173	CP $E0	Tunnel rooms are room number 224 and above
C175	JP NC,$C5B5	If we're in one of these, skip out of this routine as tunnel data is different from room data
Identify offset for room scenery graphics. Scenery graphics are different for 'brick' (e.g. Gatehouse level - offset = 0) or 'cavern' (e.g. Mines of Madness - offset = 12) style levels - see C265 and C2F8 for graphic examples In the address table at 97C3, advancing 12 addresses (=24 bytes) forward from a 'brick' level scenery graphic gives you the 'cavern' level For example, 97E5 and 97FD are the graphic addresses for the vertical wall section.
C178	CP $53	Rooms 1-82 are 'brick' style levels (e.g. Gatehouse Level). Is the room number less than 83?
C17A	LD A,$00	...If so, graphic address pointer offset is zero
C17C	JR C,$C180
C17E	LD A,$0C	If room number is 83 or above (e.g. Mines of Madness), graphic address offset is 12
C180	LD ($EB77),A	Store level type graphic address offset
The next set of instructions reset the room position:
C183	LD HL,$0000
C186	LD ($EB4C),HL	Set horizontal (EB4C) & vertical (EB4D) movement speed to zero
C189	LD ($EB47),HL	Set horizontal room position to zero
C18C	LD ($EB49),HL	Set vertical room position to zero
C18F	LD A,$40	Set vertical room position to zero
C191	LD ($EB4B),A	This byte is set to 64 for 'standard' rooms, 254/255 for tunnels (byte 9 of data set at 7C00)
C194	LD A,$20
C196	LD ($EB43),A	Room item type = room (general). This is the first data set stored in the room data sets at 7C00 and indicates the base room position/attributes
C199	LD A,$02	Item properties byte. Because this is just the general room/viewport position & data, can just set bit 1 (2) = hidden (nothing to draw)
C19B	LD ($EB4E),A
C19E	CALL $E0B0	Copy the 16 bytes of room data from working buffer at EB43 to the first of the room item data sets at 7C00
C1A1	LD A,$05	Resets the item properties ready for the next room item. Default setting sets bits 0 (visible on-screen) and 2 (needs to be erased before re-drawing)
C1A3	LD ($EB4E),A
C1A6	LD A,$50	Starting value for the room's vertical position (viewport), in pixels, from top of room area (room alignment)
C1A8	LD ($EB79),A
C1AB	LD A,$04	Starting value for the room's horizontal position (viewport), in half-character (4 pixel) steps from left of room area
C1AD	LD ($EB78),A
Prepare address pointers for the start of the room's data set:
C1B0	LD HL,($EB7A)	Get address pointer for the room data set in the table at 61A9
C1B3	LD A,(HL)	Get (first) room data set byte - this indicates the room size, in sections Trivia - Setting the scene(ry)
C1B4	INC HL	Increment address pointer to the second byte in the table (containing scenery data)
C1B5	LD ($EB7A),HL	...and re-store the pointer.
C1B8	LD ($EB7C),A	Store the first byte, which indicates room size
C1BB	LD A,$01	Store the first byte, which indicates room size
C1BD	LD ($EB7D),A	Incremental counter byte starting at 1, to compare with the first data byte of the current room when positioning room scenery. Used shortly in the routine at C1E0.