The Trap Door: Routine at 61939

61939: Update Camera Follow

Used by the routine at GameStart. Adjust the camera window at Pointer_CameraRoomOrigin to follow the target entity.
If the camera-follow delay is non-zero, tick it down; otherwise scroll the window toward the target.
Update_CameraFollow	61939	LD A,(29450)	Load A with the camera-follow delay (CameraFollowDelay).
	61942	OR A	Is the camera-follow delay (CameraFollowDelay) zero? If so, jump to Update_CameraFollow_Active.
	61943	JR Z,Update_CameraFollow_Active
	61945	DEC A	Decrease A by one.
	61946	LD (29450),A	Set the camera-follow delay (CameraFollowDelay).
	61949	RET	Return.
Camera delay expired: point at the follow entity (StateData_Berk) and track it against Pointer_CameraRoomOrigin.
Update_CameraFollow_Active	61950	LD IX,37019	Point IX at the camera-follow entity (StateData_Berk).
	61954	LD DE,(29435)	Load DE with the camera room-origin pointer (Pointer_CameraRoomOrigin).
	61958	LD B,32	Load B with loop count 32.
Probe whether the follow entity sits inside the camera X window.
Update_CameraFollow_ProbeX	61960	LD A,(IX+7)	Load A with the current entity's x-coordinate.
	61963	ADD A,2	A+=2.
	61965	CP E	Is A less than E? If so, jump to Update_CameraFollow_ScrollLeft.
	61966	JR C,Update_CameraFollow_ScrollLeft
	61968	LD C,A	Keep A in C for the next calculation.
	61969	LD A,D	Copy D into A for later use.
	61970	CP C	Is A less than C? If so, jump to Update_CameraFollow_ScrollRight.
	61971	JR C,Update_CameraFollow_ScrollRight
	61973	RET	Return.
Scroll the camera origin right by 32 until the follow entity is centred.
Update_CameraFollow_ScrollRight	61974	LD A,E	Copy the saved low byte from E into A.
	61975	CP 160	Is A equal to 160? If so, jump to Update_CameraFollow_WrapLeft.
	61977	JR Z,Update_CameraFollow_WrapLeft
	61979	ADD A,B	A+=B.
	61980	LD E,A	Copy A into E as a saved coordinate / value.
	61981	LD D,A	Copy A into D as a saved coordinate / value.
	61982	ADD A,B	A+=B.
	61983	LD D,A	Copy A into D as a saved coordinate / value.
	61984	LD (29435),DE	Store DE in Pointer: Camera Room Origin (Pointer_CameraRoomOrigin).
	61988	JR Update_CameraFollow_ProbeX	Jump to Update_CameraFollow_ProbeX to continue the loop.
Wrap the follow entity left by 160 when the camera hits the right edge.
Update_CameraFollow_WrapLeft	61990	LD A,(IX+7)	Load A with the current entity's x-coordinate.
	61993	SUB 160	A-=160.
	61995	LD (IX+7),A	Set the current entity's x-coordinate.
	61998	JR Update_CameraFollow_AdjustXExtent	Jump to Update_CameraFollow_AdjustXExtent to refresh the follow entity's x-extent.
Scroll the camera origin left by 32 until the follow entity is centred.
Update_CameraFollow_ScrollLeft	62000	LD A,E	Copy the saved low byte from E into A.
	62001	CP 32	Is A equal to 32? If so, jump to Update_CameraFollow_WrapRight.
	62003	JR Z,Update_CameraFollow_WrapRight
	62005	SUB B	Subtract B from A.
	62006	LD E,A	Copy A into E as a saved coordinate / value.
	62007	LD A,D	Copy D into A for later use.
	62008	SUB B	Subtract B from A.
	62009	LD D,A	Copy A into D as a saved coordinate / value.
	62010	LD (29435),DE	Store DE in Pointer: Camera Room Origin (Pointer_CameraRoomOrigin).
	62014	JR Update_CameraFollow_ProbeX	Jump to Update_CameraFollow_ProbeX to continue the loop.
Wrap the follow entity right by 160 when the camera hits the left edge.
Update_CameraFollow_WrapRight	62016	LD A,(IX+7)	Load A with the current entity's x-coordinate.
	62019	ADD A,160	A+=160.
	62021	LD (IX+7),A	Set the current entity's x-coordinate.
Refresh the follow entity's X-extent after a wrap and keep probing.
Update_CameraFollow_AdjustXExtent	62024	ADD A,5	A+=5.
	62026	LD (IX+8),A	Set the current entity's x-extent.
	62029	JR Update_CameraFollow_ProbeX	Jump to Update_CameraFollow_ProbeX to continue the loop.