Atic Atac: Routine at 7DC3

Used by the routines at DrawRoom and EnterRoom.

Runs the game one entity at a time. Whenever FRAMES has changed since the last time, UpdateFixedEntities runs the handlers of the three fixed entities starting at Player. Each entity from ItemEntities onwards that is in the same room as the player is then given to ProcessAction, and every 16-byte record from CreatureRecords onwards after that. Finally the room items are processed by DrawRoom. If the room has not been drawn yet (bit 0 of GameFlags is clear) the entities are skipped and DrawRoom is run immediately.

Used by the routines at DrawRoom and EnterRoom. Runs the game one entity at a time. Whenever FRAMES has changed since the last time, UpdateFixedEntities runs the handlers of the three fixed entities starting at Player. Each entity from ItemEntities onwards that is in the same room as the player is then given to ProcessAction, and every 16-byte record from CreatureRecords onwards after that. Finally the room items are processed by DrawRoom. If the room has not been drawn yet (bit 0 of GameFlags is clear) the entities are skipped and DrawRoom is run immediately.
MainLoop	7DC3	LD SP,$5E00	Set stack pointer to 5E00.
	7DC6	EI	Enable interrupts.
	7DC7	XOR A	Reset the number of creatures in NumCreatures to zero.
	7DC8	LD ($5E25),A	Reset the number of creatures in NumCreatures to zero.
	7DCB	LD IX,$EAA8	Point IX at the first entity after the three fixed entities at ItemEntities.
	7DCF	LD A,($5E14)	Jump to MainLoop_Entities if the entities in the room have already been drawn (bit 0 of GameFlags is set).
	7DD2	BIT 0,A
	7DD4	JR NZ,MainLoop_Entities
	7DD6	LD IX,$EEE0	Point IX at the end of the entity table, so that no entities are processed at RoomItemEntities.
	7DDA	JR DrawRoom	Jump to DrawRoom to draw the room.
Each pass of this loop considers one of the 8-byte entities.
MainLoop_Entities	7DDC	LD A,($5C78)	Fetch the low byte of FRAMES into C (using A).
	7DDF	LD C,A	Fetch the low byte of FRAMES into C (using A).
	7DE0	LD A,($5E03)	Fetch the FRAMES value from the previous pass.
	7DE3	CP C	Call UpdateFixedEntities if FRAMES has changed since it was last stored in LastFrame.
	7DE4	CALL NZ,UpdateFixedEntities
	7DE7	LD A,($EA91)	Fetch the room of the player.
	7DEA	CP (IX+$01)	Compare it with the room of this entity.
	7DED	LD HL,$7DF3	Point HL at the address for the handler to return to at MainLoop_NextEntity.
	7DF0	JP Z,ProcessAction	Process the entity with ProcessAction if it is in the same room as the player.
Move on to the next 8-byte entity.
MainLoop_NextEntity	7DF3	LD DE,$0008	DE=0008 (the size of an entity).
	7DF6	ADD IX,DE	Move IX on to the next entity.
	7DF8	PUSH IX	Copy IX to HL (using the stack).
	7DFA	POP HL	Copy IX to HL (using the stack).
	7DFB	LD DE,$EE60	Point DE at the end of the 8-byte entities at CreatureRecords.
	7DFE	AND A	Jump back to MainLoop_Entities until IX reaches CreatureRecords.
	7DFF	SBC HL,DE
	7E01	JR C,MainLoop_Entities
Now work through the 16-byte records. These are processed no matter which room the player is in.
MainLoop_Records	7E03	LD A,($5C78)	Fetch the low byte of FRAMES into C (using A).
	7E06	LD C,A	Fetch the low byte of FRAMES into C (using A).
	7E07	LD A,($5E03)	Fetch the FRAMES value from the previous pass.
	7E0A	CP C	Call UpdateFixedEntities if FRAMES has changed since it was last stored in LastFrame.
	7E0B	CALL NZ,UpdateFixedEntities
	7E0E	LD HL,$7E13	Point HL at the address for the handler to return to at MainLoop_NextRecord.
	7E11	JR ProcessAction	Jump to ProcessAction to process the record.
MainLoop_NextRecord	7E13	LD DE,$0010	DE=0010 (the size of a record).
	7E16	ADD IX,DE	Move IX on to the next record.
	7E18	PUSH IX	Copy IX to HL (using the stack).
	7E1A	POP HL	Copy IX to HL (using the stack).
	7E1B	LD DE,$EEE0	Point DE at the end of the entity table at RoomItemEntities.
	7E1E	AND A	Jump back to MainLoop_Records until IX reaches RoomItemEntities.
	7E1F	SBC HL,DE
	7E21	JR C,MainLoop_Records