Sabre Wulf: Routine at A2BD

Used by the routine at InitialisePlayer.

Fills a table of 0200 bytes at RoomObjectTable with the objects (see SetUpRoomObjects) which are to be found in the rooms. There are two bytes for each of the 0100 rooms, so each room can hold up to two objects.

A byte is taken from the ROM (starting at an address made from GameTimer and the frame counter, so it is effectively random) for each byte of the table. If the ROM byte is 80 or more then the table byte is zero, which means there is no object. Otherwise the table byte is made up from:

Bits 6-7: which of the room's four positions to use (taken from the byte count)
Bits 0-3: the type of object (taken from the random seed at RandomNumber)

This is used when a new game is started.

Used by the routine at InitialisePlayer. Fills a table of 0200 bytes at RoomObjectTable with the objects (see SetUpRoomObjects) which are to be found in the rooms. There are two bytes for each of the 0100 rooms, so each room can hold up to two objects. A byte is taken from the ROM (starting at an address made from GameTimer and the frame counter, so it is effectively random) for each byte of the table. If the ROM byte is 80 or more then the table byte is zero, which means there is no object. Otherwise the table byte is made up from: Bits 6-7: which of the room's four positions to use (taken from the byte count) Bits 0-3: the type of object (taken from the random seed at RandomNumber) This is used when a new game is started.
GenerateRoomObjects	A2BD	LD HL,$DDEC	Point HL at the table of room objects at RoomObjectTable.
	A2C0	LD A,($5C78)	Fetch the low byte of FRAMES into E.
	A2C3	LD E,A	Fetch the low byte of FRAMES into E.
	A2C4	LD A,($9693)	Fetch the low byte of the game timer from GameTimer.
	A2C7	AND %00011111	Keep only bits 0-4.
	A2C9	LD D,A	Use it as the high byte of the ROM address in D, so DE points into the ROM.
	A2CA	LD BC,$0200	Set the number of bytes in the table in BC to 0200.
GenerateRoomObjects_Loop	A2CD	LD A,(DE)	Fetch a (random) byte from the ROM.
	A2CE	INC DE	Move onto the next ROM byte.
	A2CF	CP $80	Jump to GenerateRoomObjects_Object if the ROM byte is less than 80.
	A2D1	JR C,GenerateRoomObjects_Object
	A2D3	LD (HL),$00	Write 00 to the table, so there is no object here.
GenerateRoomObjects_Next	A2D5	INC HL	Move onto the next table byte.
GenerateRoomObjects_Count	A2D6	DEC BC	Decrease the byte counter by one.
	A2D7	LD A,B	Loop back to GenerateRoomObjects_Loop until all 0200 bytes of the table have been done.
	A2D8	OR C
	A2D9	JR NZ,GenerateRoomObjects_Loop
	A2DB	RET	Return.
Make the table byte for an object.
GenerateRoomObjects_Object	A2DC	PUSH BC	Stash the byte counter on the stack.
	A2DD	LD A,C	Fetch the low byte of the byte counter.
	A2DE	RRCA	Rotate the low byte of the byte counter right twice.
	A2DF	RRCA	Rotate the low byte of the byte counter right twice.
	A2E0	AND %11000000	Keep only bits 6-7.
	A2E2	LD C,A	Stash the position bits in C.
	A2E3	LD A,($9695)	Fetch the random seed from RandomNumber.
	A2E6	AND %00001111	Keep only bits 0-3.
	A2E8	OR C	Combine the position and the object type.
	A2E9	LD (HL),A	Write the table byte for the object.
	A2EA	INC HL	Move onto the next table byte.
Update the random seed.
	A2EB	LD A,R	Fetch the Z80 refresh register.
	A2ED	LD C,A	Stash it in C.
	A2EE	LD A,($9695)	Fetch the random seed from RandomNumber.
	A2F1	ADD A,C	Add the refresh register value to the seed.
	A2F2	LD ($9695),A	Store the new random seed in RandomNumber.
	A2F5	POP BC	Restore the byte counter from the stack.
	A2F6	JR GenerateRoomObjects_Count	Jump back to GenerateRoomObjects_Count.