Avalon: Routine at D09B

D09B: Missile fired by Maroc or a creature - check for active shield/barrier spells

Used by the routine at C89F.
...There's a missile/bolt flying around in the room..! This routine copies the missile's data from the table at 6CDC into a working (missile) buffer at EB9D. It also checks if Maroc has a counter defence spell active (SHIELD, DEFENCE etc.) Each missile type (at 6CDC) has up to THREE counter defensive barrier-type spells that will negate/repel it These are stored in bytes 5, 7 and 8 of the missile's 8-byte data set (AMULET spell repels all missiles) The following instructions check if each of these values in a missile's data set (stored in the current missile data buffer at EBA1, EBA3 and EBA4) match the currently active defensive barrier spell type If there's a match, a special missile/barrier collision routine (E286) is CALLed
D09B	LD A,($EB4E)	Missile properties byte
D09E	AND $01	Check if it's is on-screen (bit 1 is set)
D0A0	JP Z,$D141	...if not, skip out to a later instruction
D0A3	LD HL,($EB44)	Get address pointer to missile type (in table at 6CDC)
D0A6	LD BC,$0008	Copy the 8 bytes of missile data into missile working buffer table at EB9D
D0A9	LD DE,$EB9D
D0AC	LDIR
D0AE	LD A,($EB9F)	Missile attribute (INK) colour
D0B1	LD ($EAA8),A	Copy into item data buffer
D0B4	LD A,($EBA0)	Missile's event/collision type to check (stored as the 4th byte in the missile/bolt table at 6CDC)
D0B7	CP $00
D0B9	JR Z,$D0BE	If it's zero (no event), don't copy any event data (shouldn't happen as there's a value for each missile)
D0BB	CALL $E2B0	...If it's not zero, copy item event data into working buffer
COUNTER SPELL #1 CHECK
D0BE	LD A,($EAE9)	Get currently active 'effect' spell (value = 0 if none currently in effect)
D0C1	LD C,A	Copy to C register
D0C2	LD A,($EBA1)	Defence counter spell #1 (the spell in this slot is always AMULET)
D0C5	CP $00
D0C7	JR Z,$D0CC	Check for zero - if no counter spell in this slot (shouldn't happen as there's a value for every counter slot)
D0C9	CP C	Check counter spell vs current active spell number
D0CA	JR Z,$D0E0	If there's a match, can skip the next two checks straight to D0E0
COUNTER SPELL #2 CHECK
D0CC	LD A,($EBA3)	Defence counter spell #2
D0CF	CP $00	Check for zero - if no counter spell in this slot (shouldn't happen as there's a value for every counter slot)
D0D1	JR Z,$D0D6
D0D3	CP C	Check counter spell vs current active spell number
D0D4	JR Z,$D0E0	If there's a match, can skip the final check and jump straight to D0E0
COUNTER SPELL #2 CHECK
D0D6	LD A,($EBA4)	Defence counter spell #3
D0D9	CP $00	heck for zero - if no counter spell in this slot (shouldn't happen as there's a value for every counter slot)
D0DB	JR Z,$D116
D0DD	CP C	Check counter spell vs current active spell number
D0DE	JR NZ,$D116	If there's NO match, jump out of the routine here
The following instructions are redundant (possibly duplicated), as CP C has already happened in a previous check
D0E0	CP C	-
D0E1	JR NZ,$D116	-
There's a match between the missile/bolt fired and an active shielding spell around Maroc that will negate/deflect it The following instructions check for a collision against Maroc's flickering shielding/protective spell
D0E3	LD C,$01	For the usual collision/event detection routine (DFCD) the C register is set an event/collision type. On this occasion loading the C register is unnecessary as it's not actually needed/used for this (special) missile routine.
D0E5	CALL $E286	Check for a collision between the fired bolt/missile and the shield/barrier around Maroc
D0E8	CP $00	The A register is returned with 0 if no collision, or 8 (this byte is used elsewhere for the accompanying sound effect) if there's a collision
D0EA	JR Z,$D116	If no collision, jump out of this routine/check