Avalon: Routine at CDD7

CDD7: Change creature behaviour based on Maroc's magic

Used by the routine at CD88.
The different creatures in Avalon have their own distinct movement patterns. For example, wraiths will occasionally dart towards or away from Maroc. Goblin missile throwers stop in one place and fire missiles at Maroc from a distance. Movement patterns are affected by Maroc's active spells (particularly UNSEEN and FREEZE), at different intervals using the game cycle timer/counter stored at EAAA.
CDD7	LD A,($EB46)	Creature type
CDDA	CP $08	Guardian of Chaos
CDDC	JP Z,$CF0B	Guardian of Chaos
CDDF	JP C,$CE71	If creature type < 8 then it's a warlock, If so, skip this routine as they have a different movement pattern to other creatures
CDE2	CP $0B	Wraith
CDE4	JR Z,$CE2E	Wraith
CDE6	CP $09	Goblin warrior
CDE8	JP Z,$CF3E	Goblin warrior
CDEB	CP $0C	Demon
CDED	JP Z,$CE2E	Demon
Goblin missile thrower (creature type #10) Goblin missile throwers won't fire any missiles at Maroc if UNSEEN or FREEZE spell is active
CDF0	LD A,($EB4E)	Creature properties byte
CDF3	AND $01	Creature properties byte
CDF5	JP Z,$CF0B	If creature is off screen, check if its movement needs to be changed due to the UNSEEN spell being active
CDF8	LD A,($EB50)	Creature is on-screen. Get graphic frame number offset
CDFB	AND $07	Keep bits 0-2
CDFD	CP $03	Is the graphic frame #3?
CDFF	JR NZ,$CE12	If not, jump to the next section to determine the creature's movement
If the creature has reached frame 3, it can fire a missile (as long as FREEZE or UNSEEN aren't active)
CE01	LD A,($EAE9)	Currently active spell
CE04	CP $09	Check if the UNSEEN spell is active
CE06	JR Z,$CE12	Jump to CE12 if UNSEEN is active
CE08	LD A,($EC9C)	Check FREEZE spell timer counter
CE0B	CP $00	Check FREEZE spell timer counter
CE0D	JR NZ,$CE12	If counter is > 0, FREEZE spell is active - jump to CE12
CE0F	JP $CF58	Neither FREEZE or UNSEEN is active so initialize a missile
UNSEEN or FREEZE spell is active
CE12	LD A,($EAAA)	Game cycle counter
CE15	AND $0F	Check bits 0-3
CE17	JP Z,$CF0B	Every 16th game cycle check the UNSEEN spell and alter the creature's movement accordingly
CE1A	CP $0C
CE1C	JR Z,$CE4F	On each game cycle #12 (of 16) randomize the creature's movement
CE1E	CP $00
CE20	JP NZ,$D04B
CE23	LD A,$00	On every 16th game cycle, stop moving:
CE25	LD ($EB4C),A	Set horizontal movement speed/direction to zero
CE28	LD ($EB4D),A	Set vertical movement speed/direction to zero
CE2B	JP $D04B	Set vertical movement speed/direction to zero
Jump here from CDD7 if creature type is WRAITH or DEMON. These two creatures can 'sniff out' powerful magic. If Maroc has UNSEEN active, they are able to home in on his position, making them potentially more dangerous, though DEMONs will not fire missiles which tend to be more difficult to avoid They will also move towards Maroc's screen position if he casts ANY 'powerful' spell (i.e. spell number >=4)
CE2E	LD A,($EAEC)	Get activated spell
CE31	CP $04	If spell number >=4, jump to CF1D
CE33	JP NC,$CF1D	If spell number >=4, jump to CF1D
CE36	LD A,($EAE9)	Check for currently active effect spells
CE39	CP $09	Check for currently active effect spells
CE3B	JP Z,$CF1D	If UNSEEN spell is active, jump to CF1D
CE3E	LD A,($EAAA)	Game cycle counter
CE41	AND $1F	Check if any bits 0-4 set
CE43	CP $00	Check if any bits 0-4 set
CE45	JR NZ,$CE69	If not, skip the next two sets of instructions
Every 32 game cycles Wraiths will change their movement direction Demons will fire a missile at Maroc
CE47	LD A,($EB46)	Check if creature is type number #12 (demon)
CE4A	CP $0C	Check if creature is type number #12 (demon)
CE4C	JP Z,$CF58	If so, go and initialize a missile/bolt Otherwise it's a wraith, so continue to the next instructions to randomize its movement
Randomize creature movement Changes movement speeds/directions for: Goblin warrior if Maroc has cast a powerful spell (CF3E) Goblin missile thrower, every 16 game cycles Guardian of Chaos if the UNSEEN spell is active CF0B Wraith, every 32 game cycles
CE4F	CALL $DB06	Generate pseudo-random number
CE52	LD C,A	Temp store in C register
CE53	AND $0F	Only need bits 0-3 (values 0-15)
CE55	SUB $07	Subtract 7, so values between -7 and +8
CE57	ADD A,A	Subtract 7, so values between -7 and +8
CE58	ADD A,A	Multiply by 4, so values now between -28 and +32 (in multiples of 4)
CE59	LD ($EB4C),A	Store as creature's horizontal speed (negative numbers = left, positive = right)
CE5C	LD A,C	Retrieve stored pseudo-random number
CE5D	RRA	Retrieve stored pseudo-random number
CE5E	RRA	Divide by 4 (creates a different number from the previous one)
CE5F	AND $0F	Keep bits 0-3 (values 0-15)
CE61	SUB $07	Subtract 7, so values now between -7 and +8
CE63	LD ($EB4D),A	Store as creature's vertical speed (negative numbers = up, positive = down)
CE66	JP $D04B
WRAITH or DEMON movement - continued from CE45
CE69	AND $07	(Game timer counter) - check bits 0-2
CE6B	JP NZ,$D04B	(Game timer counter) - check bits 0-2
CE6E	JP $CF1D	Every 8 game cycles, re-calculate the creature's homing trajectory based on Maroc's position