Avalon: Routine at 49498

49498: Room initialization - identify room data set and scenery style, reset room/viewport position


Find the current's room data set in the table at 25001:
49498	LD HL,(56055)	Pointer to series of room data sets at 25001.
49501	LD A,(60087)	Get room number
49504	LD C,A	Store in C register
49505	LD B,1	Set incremental compare counter to compare room number against
Identify data set for current room from list at 25001
49507	LD A,C
49508	CP B
49509	JR Z,49520	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)
49511	LD A,(HL)	Get byte of room data set
49512	INC HL	Increment it
49513	CP 255	Are we at an end-of-data-set marker?
49515	JR NZ,49511	Continue till we are
49517	INC B	We're at the end of this set. Increment the counter
49518	JR 49507	Keep comparing until we're at the right place for the room
Data set for current room identified
49520	LD (60282),HL	Store address pointer for current room data bank.
Check if the room is a vertical tunnel
49523	CP 224	Tunnel rooms are room number 224 and above
49525	JP NC,50613	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 49765 and 49912 for graphic examples In the address table at 38851, advancing 12 addresses (=24 bytes) forward from a 'brick' level scenery graphic gives you the 'cavern' level For example, 38885 and 38909 are the graphic addresses for the vertical wall section.
49528	CP 83	Rooms 1-82 are 'brick' style levels (e.g. Gatehouse Level). Is the room number less than 83?
49530	LD A,0	...If so, graphic address pointer offset is zero
49532	JR C,49536
49534	LD A,12	If room number is 83 or above (e.g. Mines of Madness), graphic address offset is 12
49536	LD (60279),A	Store level type graphic address offset
The next set of instructions reset the room position:
49539	LD HL,0
49542	LD (60236),HL	Set horizontal (60236) & vertical (60237) movement speed to zero
49545	LD (60231),HL	Set horizontal room position to zero
49548	LD (60233),HL	Set vertical room position to zero
49551	LD A,64	Set vertical room position to zero
49553	LD (60235),A	This byte is set to 64 for 'standard' rooms, 254/255 for tunnels (byte 9 of data set at 31744)
49556	LD A,32
49558	LD (60227),A	Room item type = room (general). This is the first data set stored in the room data sets at 31744 and indicates the base room position/attributes
49561	LD A,2	Item properties byte. Because this is just the general room/viewport position & data, can just set bit 1 (2) = hidden (nothing to draw)
49563	LD (60238),A
49566	CALL 57520	Copy the 16 bytes of room data from working buffer at 60227 to the first of the room item data sets at 31744
49569	LD A,5	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)
49571	LD (60238),A
49574	LD A,80	Starting value for the room's vertical position (viewport), in pixels, from top of room area (room alignment)
49576	LD (60281),A
49579	LD A,4	Starting value for the room's horizontal position (viewport), in half-character (4 pixel) steps from left of room area
49581	LD (60280),A
Prepare address pointers for the start of the room's data set:
49584	LD HL,(60282)	Get address pointer for the room data set in the table at 25001
49587	LD A,(HL)	Get (first) room data set byte - this indicates the room size, in sections Trivia - Setting the scene(ry)
49588	INC HL	Increment address pointer to the second byte in the table (containing scenery data)
49589	LD (60282),HL	...and re-store the pointer.
49592	LD (60284),A	Store the first byte, which indicates room size
49595	LD A,1	Store the first byte, which indicates room size
49597	LD (60285),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 49632.