Sabre Wulf: Routine at 41661

Used by the routine at InitialisePlayer.

Fills a table of 512 bytes at RoomObjectTable with the objects (see SetUpRoomObjects) which are to be found in the rooms. There are two bytes for each of the 256 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 128 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 512 bytes at RoomObjectTable with the objects (see SetUpRoomObjects) which are to be found in the rooms. There are two bytes for each of the 256 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 128 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	41661	LD HL,56812	Point HL at the table of room objects at RoomObjectTable.
	41664	LD A,(23672)	Fetch the low byte of FRAMES into E.
	41667	LD E,A	Fetch the low byte of FRAMES into E.
	41668	LD A,(38547)	Fetch the low byte of the game timer from GameTimer.
	41671	AND %00011111	Keep only bits 0-4.
	41673	LD D,A	Use it as the high byte of the ROM address in D, so DE points into the ROM.
	41674	LD BC,512	Set the number of bytes in the table in BC to 512.
GenerateRoomObjects_Loop	41677	LD A,(DE)	Fetch a (random) byte from the ROM.
	41678	INC DE	Move onto the next ROM byte.
	41679	CP 128	Jump to GenerateRoomObjects_Object if the ROM byte is less than 128.
	41681	JR C,GenerateRoomObjects_Object
	41683	LD (HL),0	Write 0 to the table, so there is no object here.
GenerateRoomObjects_Next	41685	INC HL	Move onto the next table byte.
GenerateRoomObjects_Count	41686	DEC BC	Decrease the byte counter by one.
	41687	LD A,B	Loop back to GenerateRoomObjects_Loop until all 512 bytes of the table have been done.
	41688	OR C
	41689	JR NZ,GenerateRoomObjects_Loop
	41691	RET	Return.
Make the table byte for an object.
GenerateRoomObjects_Object	41692	PUSH BC	Stash the byte counter on the stack.
	41693	LD A,C	Fetch the low byte of the byte counter.
	41694	RRCA	Rotate the low byte of the byte counter right twice.
	41695	RRCA	Rotate the low byte of the byte counter right twice.
	41696	AND %11000000	Keep only bits 6-7.
	41698	LD C,A	Stash the position bits in C.
	41699	LD A,(38549)	Fetch the random seed from RandomNumber.
	41702	AND %00001111	Keep only bits 0-3.
	41704	OR C	Combine the position and the object type.
	41705	LD (HL),A	Write the table byte for the object.
	41706	INC HL	Move onto the next table byte.
Update the random seed.
	41707	LD A,R	Fetch the Z80 refresh register.
	41709	LD C,A	Stash it in C.
	41710	LD A,(38549)	Fetch the random seed from RandomNumber.
	41713	ADD A,C	Add the refresh register value to the seed.
	41714	LD (38549),A	Store the new random seed in RandomNumber.
	41717	POP BC	Restore the byte counter from the stack.
	41718	JR GenerateRoomObjects_Count	Jump back to GenerateRoomObjects_Count.