posting this just cause someone on the FB group was asking about it and I wanted to give them a link. It's pretty straightforward but also probably poorly written. If someone wants to take a crack at a better version, feel free.
The reason this is set up how it is was to have a single player object control all of the spell FX for one character, with one action step per spell. Advancing an action step normally therefore can't be used as a timer since it would change the graphics of the spell. Instead, I set the end action AI to "repeat" and the animation to "loop".
From there the AI posted below handles a counter used by the player's spells that can be accessed in a number of other routines. I couldn't increment the timer elsewhere for this spell because there's no way to easily predict/control how often the spell AI fires, and if the counter is run down outside of the spell AI, the spell inevitably desynchs.
then elsewhere, in doHandlePhysics, after this block, I edited as follows to allow for some action-step based checks to alter the max speed of the spells depending on which action step [and therefore which spell sprite] was currently visible. One is a flame that moves at a fair clip, and the earth spell that was asked about in the FB group needed to look more like it was moving in an arc [using the code from the above section].
Then, at the next bit of doHandlePhysics:
Those two bits added to doHandlePhysics are because objects only get one max speed, and in the overhead module, that speed is the same for X and Y values, making it hard to cause an object to move in an arc.
The reason this is set up how it is was to have a single player object control all of the spell FX for one character, with one action step per spell. Advancing an action step normally therefore can't be used as a timer since it would change the graphics of the spell. Instead, I set the end action AI to "repeat" and the animation to "loop".
From there the AI posted below handles a counter used by the player's spells that can be accessed in a number of other routines. I couldn't increment the timer elsewhere for this spell because there's no way to easily predict/control how often the spell AI fires, and if the counter is run down outside of the spell AI, the spell inevitably desynchs.
Code:
note - this is an enemy AI script
;earth - move up, drift, and crash down
+isEarth
INX
LDA Object_type,x
STA temp1
DEX
LDA Object_type,x
CMP temp1
BEQ +leftSideRockToss
JMP rightSideRockToss
+leftSideRockToss
LDA gameTimerHi
CMP #$01
BNE +nextCheck
LDA #UPLEFT
JMP +headingLeft
+nextCheck
CMP #$02
BNE +nextCheck
LDA #LEFT
JMP +headingLeft
+nextCheck
CMP #$03
BNE +nextCheck
LDA #DOWNLEFT
JMP +headingLeft
+nextCheck
LDA Object_status,x
AND #$3F
STA Object_status,x
JMP doneSpellAI
+headingLeft
STA temp1
JMP +isMoving
rightSideRockToss:
LDA gameTimerHi
AND #%00000111
CMP #$01
BNE +nextCheck
LoadObjectSubPalettes #$3B, #$00
LDA #UPRIGHT
JMP +headingRight
+nextCheck
CMP #$02
BNE +nextCheck
LDA #RIGHT
JMP +headingRight
+nextCheck
CMP #$03
BNE +nextCheck
LoadObjectSubPalettes #$00, #$00
LDA #DOWNRIGHT
JMP +headingRight
+nextCheck
LoadObjectSubPalettes #$3B, #$04
LoadObjectSubPalettes #$3B, #$08
LoadObjectSubPalettes #$3B, #$12
LDA #$00
STA gameTimerHi
LDA #%10000000
STA gameTimerLo
LDA Object_status,x
AND #$3F
STA Object_status,x
JMP doneSpellAI
+headingRight
INC gameTimerHi
STA temp1then elsewhere, in doHandlePhysics, after this block, I edited as follows to allow for some action-step based checks to alter the max speed of the spells depending on which action step [and therefore which spell sprite] was currently visible. One is a flame that moves at a fair clip, and the earth spell that was asked about in the FB group needed to look more like it was moving in an arc [using the code from the above section].
Code:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;find this chunk
+notHurt
LDY Object_type,x
LDA ObjectMaxSpeed,y
ASL
ASL
ASL
ASL
;AND #%00001111
STA myMaxSpeed
LDA ObjectMaxSpeed,y
LSR
LSR
LSR
LSR
STA myMaxSpeed+1
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;this next bit is added to allow for a context-based modification of max speed for a single action step of a single player object [using player object 05]
LDA Object_type,x
CMP #$05
BNE +notFlameOrEarth
LDA Object_frame,x
AND #%00111000
CMP #%00001000
BNE +notFlameOrEarth
LDA #$C0
STA myMaxSpeed
LDA #$00
STA myMaxSpeed+1
+notFlameOrEarth
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;end of stuff for max accel modulation added by me to doHandlePhysics
;;; now high max speed byte is the actual high byte of speedThen, at the next bit of doHandlePhysics:
Code:
skipDoHdec:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;!!!!!!!!!!!!!!!!!!!!
;;; ***** added by me to run that check against the stones for earth spell!
LDA Object_type,x
CMP #$05
BNE +isNotEarthStone
LDA Object_frame,x
AND #%00111000
CMP #%00011000
BNE +isNotEarthStone
LDA myMaxSpeed
LSR
LSR
LSR
STA Object_h_speed_lo,x
LDA #$00
STA Object_h_speed_hi,x
+isNotEarthStone
;;;;;;;;;;;;;;;;;;;;; *** done addThose two bits added to doHandlePhysics are because objects only get one max speed, and in the overhead module, that speed is the same for X and Y values, making it hard to cause an object to move in an arc.
