Thwomp mad

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;; Mad Thwomp, by yoshicookiezeus
;; Based on mikeyk's Thwomp disassembly and smwedit's Reverse Thwomp
;;
;; Description: A Thwomp that, when triggered, keeps smashing up and down.
;;
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			; symbolic names for RAM addresses (don't change these)
			!SPRITE_Y_SPEED  = $AA
			!SPRITE_X_SPEED  = $B6
			!SPRITE_STATE    = $C2
			!SPRITE_Y_POS    = $D8
			!ORIG_Y_POS      = $151C
			!EXPRESSION      = $1528
			!FREEZE_TIMER    = $1540
			!SPR_OBJ_STATUS  = $1588
			!H_OFFSCREEN     = $15A0
			!V_OFFSCREEN     = $186C

			; definitions of bits (don't change these)
			!IS_ON_GROUND    = $04
			!IS_ON_CEILING   = $08

			; sprite data
			!SPRITE_GRAVITY  = $08
			!MAX_Y_SPEED1    = $4E
			!MAX_Y_SPEED2    = $C2
			!RISE_SPEED      = $FF
			!TIME_TO_SHAKE   = $00
			!SOUND_EFFECT    = $09
			!TIME_ON_GROUND  = $0C
			!ANGRY_TILE      = $CA

X_OFFSET:		db $FC,$04,$FC,$04,$00
Y_OFFSET:		db $00,$00,$10,$10,$08
TILE_MAP:		db $8E,$8E,$AE,$AE,$C8
PROPERTIES:		db $03,$43,$03,$43,$03

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; sprite init JSL
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

			PRINT "INIT ",pc
			LDA !SPRITE_Y_POS,x
			STA !ORIG_Y_POS,x
			LDA $E4,x
			CLC
			ADC #$08
			STA $E4,x
			RTL


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; sprite code JSL
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

			PRINT "MAIN ",pc
			PHB
			PHK
			PLB
			JSR SPRITE_CODE_START
			PLB
			RTL


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; sprite main code
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RETURN:			RTS

SPRITE_CODE_START:	JSR SUB_GFX

			LDA $14C8,x		; RETURN if sprite status != 8
			CMP #$08
			BNE RETURN

			LDA $9D			; RETURN if sprites locked
			BNE RETURN

			JSR SUB_OFF_SCREEN_X0	; only process sprite while on screen

			JSL $01A7DC		; interact with mario

			LDA !SPRITE_STATE,x
			CMP #$01
			BEQ FALLING
			CMP #$02
			BEQ RISING

;-----------------------------------------------------------------------------------------
; state 0
;-----------------------------------------------------------------------------------------

HOVERING:		LDA !V_OFFSCREEN,x	;fall if offscreen vertically
			BNE SET_FALLING

			LDA !H_OFFSCREEN,x	;RETURN if offscreen horizontally
			BNE RETURN0

			JSR SUB_HORZ_POS	;determine if mario is close and act accordingly
			TYA
			STA $157C,x
			STZ !EXPRESSION,x
			LDA $0F
			CLC
			ADC #$40
			CMP #$80
			BCS THWOMP_4
			LDA #$01
			STA !EXPRESSION,x
THWOMP_4:		LDA $0F
			CLC
			ADC #$24
			CMP #$50
			BCS RETURN0

SET_FALLING:		LDA #$02		;set expression
			STA !EXPRESSION,x

			INC !SPRITE_STATE,x	;chage state to FALLING

			LDA #$00
			STA !SPRITE_Y_SPEED,x	;set initial speed

RETURN0:			RTS

;-----------------------------------------------------------------------------------------
; state 1
;-----------------------------------------------------------------------------------------

FALLING:			LDA !FREEZE_TIMER,x	;if we're still waiting on the ground, RETURN
			BNE RETURN2
			JSL $01801A		;apply speed

			LDA !SPRITE_Y_SPEED,x	;increase speed if below the max
			CMP #!MAX_Y_SPEED1
			BCS DONT_INC_SPEED1
			ADC #!SPRITE_GRAVITY
			STA !SPRITE_Y_SPEED,x
DONT_INC_SPEED1:
			JSL $019138		;interact with objects

			LDA !SPR_OBJ_STATUS,x	;RETURN if not on the ground
			AND #!IS_ON_GROUND
			BEQ RETURN1

			JSR SUB_9A04		; ?? speed related

			LDA #!TIME_TO_SHAKE	;shake ground
			STA $1887

			LDA #!SOUND_EFFECT	;play sound effect
			STA $1DFC

			LDA #!TIME_ON_GROUND	;set time to stay on ground
			STA !FREEZE_TIMER,x

			INC !SPRITE_STATE,x	;go to RISING state
RETURN1:			RTS

;-----------------------------------------------------------------------------------------
; state 2
;-----------------------------------------------------------------------------------------

RISING:              	LDA !FREEZE_TIMER,x	;if we're still waiting on the ground, RETURN
			BNE RETURN2
			JSL $01801A		;apply speed

			LDA !SPRITE_Y_SPEED,x	;increase speed if below the max
			CMP #!MAX_Y_SPEED2
			BMI DONT_INC_SPEED2
			SBC #!SPRITE_GRAVITY
			STA !SPRITE_Y_SPEED,x
DONT_INC_SPEED2:
			JSL $019138		;interact with objects

			LDA !SPR_OBJ_STATUS,x	;RETURN if not on the ceiling
			AND #!IS_ON_CEILING
			BEQ RETURN2

			JSR SUB_9A04		; ?? speed related

			LDA #!TIME_TO_SHAKE	;shake ground
			STA $1887

			LDA #!SOUND_EFFECT	;play sound effect
			STA $1DFC

			LDA #!TIME_ON_GROUND	;set time to stay on ground
			STA !FREEZE_TIMER,x

			DEC !SPRITE_STATE,x	;go to FALLING state
RETURN2:			RTS


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; graphics routine
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SUB_GFX:			JSR GET_DRAW_INFO

			LDA !EXPRESSION,x
			STA $02
			PHX
			LDX #$03
			CMP #$00
			BEQ LOOP_START
			INX
LOOP_START:		LDA $00
			CLC
			ADC X_OFFSET,x
			STA $0300,y

			LDA $01
			CLC
			ADC Y_OFFSET,x
			STA $0301,y

			LDA PROPERTIES,x
			ORA $64
			STA $0303,y

			LDA TILE_MAP,x
			CPX #$04
			BNE NORMAL_TILE
			PHX
			LDX $02
			CPX #$02
			BNE NOT_ANGRY
			LDA #!ANGRY_TILE
NOT_ANGRY:		PLX
NORMAL_TILE:		STA $0302,y

			INY
			INY
			INY
			INY
			DEX
			BPL LOOP_START

			PLX

			LDY #$02		; \ 460 = 2 (all 16x16 tiles)
			LDA #$04		;  | A = (number of tiles drawn - 1)
			JSL $01B7B3		; / don't draw if offscreen
			RTS			; RETURN


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; speed related
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SUB_9A04:            LDA !SPR_OBJ_STATUS,x
			BMI THWOMP_1
			LDA #$00
			LDY $15B8,x
			BEQ THWOMP_2
THWOMP_1:            LDA #$18
THWOMP_2:            STA !SPRITE_Y_SPEED,x
			RTS


;###############################################################################################
;###############################################################################################
;###############################################################################################
; ROUTINES FROM THE LIBRARY ARE PASTED BELOW
; You should never have to modify this code
;###############################################################################################
;###############################################################################################
;###############################################################################################


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; SUB_HORZ_POS
; This routine determines which side of the sprite Mario is on.  It sets the Y register
; to the direction such that the sprite would face Mario
; It is ripped from $03B817
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SUB_HORZ_POS:		LDY #$00				;A:25D0 X:0006 Y:0001 D:0000 DB:03 S:01ED P:eNvMXdizCHC:1020 VC:097 00 FL:31642
					LDA $94					;A:25D0 X:0006 Y:0000 D:0000 DB:03 S:01ED P:envMXdiZCHC:1036 VC:097 00 FL:31642
					SEC			 ;A:25F0 X:0006 Y:0000 D:0000 DB:03 S:01ED P:eNvMXdizCHC:1060 VC:097 00 FL:31642
					SBC $E4,x				;A:25F0 X:0006 Y:0000 D:0000 DB:03 S:01ED P:eNvMXdizCHC:1074 VC:097 00 FL:31642
					STA $0F					;A:25F4 X:0006 Y:0000 D:0000 DB:03 S:01ED P:eNvMXdizcHC:1104 VC:097 00 FL:31642
					LDA $95					;A:25F4 X:0006 Y:0000 D:0000 DB:03 S:01ED P:eNvMXdizcHC:1128 VC:097 00 FL:31642
					SBC $14E0,x				;A:2500 X:0006 Y:0000 D:0000 DB:03 S:01ED P:envMXdiZcHC:1152 VC:097 00 FL:31642
					BPL SPR_L16             ;A:25FF X:0006 Y:0000 D:0000 DB:03 S:01ED P:eNvMXdizcHC:1184 VC:097 00 FL:31642
					INY			 ;A:25FF X:0006 Y:0000 D:0000 DB:03 S:01ED P:eNvMXdizcHC:1200 VC:097 00 FL:31642
SPR_L16:				RTS			 ;A:25FF X:0006 Y:0001 D:0000 DB:03 S:01ED P:envMXdizcHC:1214 VC:097 00 FL:31642


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; SUB_OFF_SCREEN
; This subroutine deals with sprites that have moved off screen
; It is adapted from the subroutine at $01AC0D
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SPR_T12:             db $40,$B0
SPR_T13:             db $01,$FF
SPR_T14:             db $30,$C0,$A0,$C0,$A0,$F0,$60,$90		;bank 1 sizes
		            db $30,$C0,$A0,$80,$A0,$40,$60,$B0		;bank 3 sizes
SPR_T15:             db $01,$FF,$01,$FF,$01,$FF,$01,$FF		;bank 1 sizes
					db $01,$FF,$01,$FF,$01,$00,$01,$FF		;bank 3 sizes

SUB_OFF_SCREEN_X1:   LDA #$02                ; \ entry point of routine determines value of $03
			BRA STORE_03            ;  | (table entry to use on horizontal levels)
SUB_OFF_SCREEN_X2:   LDA #$04                ;  |
			BRA STORE_03            ;  |
SUB_OFF_SCREEN_X3:   LDA #$06                ;  |
			BRA STORE_03            ;  |
SUB_OFF_SCREEN_X4:   LDA #$08                ;  |
			BRA STORE_03            ;  |
SUB_OFF_SCREEN_X5:   LDA #$0A                ;  |
			BRA STORE_03            ;  |
SUB_OFF_SCREEN_X6:   LDA #$0C                ;  |
			BRA STORE_03            ;  |
SUB_OFF_SCREEN_X7:   LDA #$0E                ;  |
STORE_03:			STA $03					;  |
					BRA START_SUB			;  |
SUB_OFF_SCREEN_X0:   STZ $03					; /

START_SUB:           JSR SUB_IS_OFF_SCREEN   ; \ if sprite is not off screen, RETURN
			BEQ RETURN_35           ; /
			LDA $5B                 ; \  goto VERTICAL_LEVEL if vertical level
			AND #$01                ; |
			BNE VERTICAL_LEVEL      ; /
			LDA !SPRITE_Y_POS,x               ; \
			CLC			 ; |
			ADC #$50                ; | if the sprite has gone off the bottom of the level...
			LDA $14D4,x             ; | (if adding 0x50 to the sprite y position would make the high byte >= 2)
			ADC #$00                ; |
			CMP #$02                ; |
			BPL ERASE_SPRITE        ; /    ...erase the sprite
			LDA $167A,x             ; \ if "process offscreen" flag is set, RETURN
			AND #$04                ; |
			BNE RETURN_35           ; /
			LDA $13                 ;A:8A00 X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdiZcHC:0756 VC:176 00 FL:205
			AND #$01                ;A:8A01 X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdizcHC:0780 VC:176 00 FL:205
			ORA $03                 ;A:8A01 X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdizcHC:0796 VC:176 00 FL:205
			STA $01                 ;A:8A01 X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdizcHC:0820 VC:176 00 FL:205
			TAY			 ;A:8A01 X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdizcHC:0844 VC:176 00 FL:205
			LDA $1A                 ;A:8A01 X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdizcHC:0858 VC:176 00 FL:205
			CLC			 ;A:8A00 X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdiZcHC:0882 VC:176 00 FL:205
			ADC SPR_T14,y           ;A:8A00 X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdiZcHC:0896 VC:176 00 FL:205
			ROL $00                 ;A:8AC0 X:0009 Y:0001 D:0000 DB:01 S:01F1 P:eNvMXdizcHC:0928 VC:176 00 FL:205
			CMP $E4,x               ;A:8AC0 X:0009 Y:0001 D:0000 DB:01 S:01F1 P:eNvMXdizCHC:0966 VC:176 00 FL:205
			PHP			 ;A:8AC0 X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdizCHC:0996 VC:176 00 FL:205
			LDA $1B                 ;A:8AC0 X:0009 Y:0001 D:0000 DB:01 S:01F0 P:envMXdizCHC:1018 VC:176 00 FL:205
			LSR $00                 ;A:8A00 X:0009 Y:0001 D:0000 DB:01 S:01F0 P:envMXdiZCHC:1042 VC:176 00 FL:205
			ADC SPR_T15,y           ;A:8A00 X:0009 Y:0001 D:0000 DB:01 S:01F0 P:envMXdizcHC:1080 VC:176 00 FL:205
			PLP			 ;A:8AFF X:0009 Y:0001 D:0000 DB:01 S:01F0 P:eNvMXdizcHC:1112 VC:176 00 FL:205
			SBC $14E0,x             ;A:8AFF X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdizCHC:1140 VC:176 00 FL:205
			STA $00                 ;A:8AFF X:0009 Y:0001 D:0000 DB:01 S:01F1 P:eNvMXdizCHC:1172 VC:176 00 FL:205
			LSR $01                 ;A:8AFF X:0009 Y:0001 D:0000 DB:01 S:01F1 P:eNvMXdizCHC:1196 VC:176 00 FL:205
			BCC SPR_L31             ;A:8AFF X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdiZCHC:1234 VC:176 00 FL:205
			EOR #$80                ;A:8AFF X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdiZCHC:1250 VC:176 00 FL:205
			STA $00                 ;A:8A7F X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdizCHC:1266 VC:176 00 FL:205
SPR_L31:             LDA $00                 ;A:8A7F X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdizCHC:1290 VC:176 00 FL:205
			BPL RETURN_35           ;A:8A7F X:0009 Y:0001 D:0000 DB:01 S:01F1 P:envMXdizCHC:1314 VC:176 00 FL:205
ERASE_SPRITE:        LDA $14C8,x             ; \ if sprite status < 8, permanently erase sprite
			CMP #$08                ; |
			BCC KILL_SPRITE         ; /
			LDY $161A,x             ;A:FF08 X:0007 Y:0001 D:0000 DB:01 S:01F3 P:envMXdiZCHC:1108 VC:059 00 FL:2878
			CPY #$FF                ;A:FF08 X:0007 Y:0000 D:0000 DB:01 S:01F3 P:envMXdiZCHC:1140 VC:059 00 FL:2878
			BEQ KILL_SPRITE         ;A:FF08 X:0007 Y:0000 D:0000 DB:01 S:01F3 P:envMXdizcHC:1156 VC:059 00 FL:2878
			LDA #$00                ;A:FF08 X:0007 Y:0000 D:0000 DB:01 S:01F3 P:envMXdizcHC:1172 VC:059 00 FL:2878
			STA $1938,y             ;A:FF00 X:0007 Y:0000 D:0000 DB:01 S:01F3 P:envMXdiZcHC:1188 VC:059 00 FL:2878
KILL_SPRITE:         STZ $14C8,x             ; erase sprite
RETURN_35:           RTS			 ; RETURN

VERTICAL_LEVEL:      LDA $167A,x             ; \ if "process offscreen" flag is set, RETURN
			AND #$04                ; |
			BNE RETURN_35           ; /
			LDA $13                 ; \
			LSR A                   ; |
			BCS RETURN_35           ; /
			LDA $E4,x               ; \
			CMP #$00                ;  | if the sprite has gone off the side of the level...
			LDA $14E0,x             ;  |
			SBC #$00                ;  |
			CMP #$02                ;  |
			BCS ERASE_SPRITE        ; /  ...erase the sprite
			LDA $13                 ;A:0000 X:0009 Y:00E4 D:0000 DB:01 S:01F3 P:eNvMXdizcHC:1218 VC:250 00 FL:5379
			LSR A                   ;A:0016 X:0009 Y:00E4 D:0000 DB:01 S:01F3 P:envMXdizcHC:1242 VC:250 00 FL:5379
			AND #$01                ;A:000B X:0009 Y:00E4 D:0000 DB:01 S:01F3 P:envMXdizcHC:1256 VC:250 00 FL:5379
			STA $01                 ;A:0001 X:0009 Y:00E4 D:0000 DB:01 S:01F3 P:envMXdizcHC:1272 VC:250 00 FL:5379
			TAY			 ;A:0001 X:0009 Y:00E4 D:0000 DB:01 S:01F3 P:envMXdizcHC:1296 VC:250 00 FL:5379
			LDA $1C                 ;A:001A X:0009 Y:0001 D:0000 DB:01 S:01F3 P:eNvMXdizcHC:0052 VC:251 00 FL:5379
			CLC			 ;A:00BD X:0009 Y:0001 D:0000 DB:01 S:01F3 P:eNvMXdizcHC:0076 VC:251 00 FL:5379
			ADC SPR_T12,y           ;A:00BD X:0009 Y:0001 D:0000 DB:01 S:01F3 P:eNvMXdizcHC:0090 VC:251 00 FL:5379
			ROL $00                 ;A:006D X:0009 Y:0001 D:0000 DB:01 S:01F3 P:enVMXdizCHC:0122 VC:251 00 FL:5379
			CMP !SPRITE_Y_POS,x      ;A:006D X:0009 Y:0001 D:0000 DB:01 S:01F3 P:eNVMXdizcHC:0160 VC:251 00 FL:5379
			PHP			 ;A:006D X:0009 Y:0001 D:0000 DB:01 S:01F3 P:eNVMXdizcHC:0190 VC:251 00 FL:5379
			LDA.w $001D             ;A:006D X:0009 Y:0001 D:0000 DB:01 S:01F2 P:eNVMXdizcHC:0212 VC:251 00 FL:5379
			LSR $00                 ;A:0000 X:0009 Y:0001 D:0000 DB:01 S:01F2 P:enVMXdiZcHC:0244 VC:251 00 FL:5379
			ADC SPR_T13,y           ;A:0000 X:0009 Y:0001 D:0000 DB:01 S:01F2 P:enVMXdizCHC:0282 VC:251 00 FL:5379
			PLP			 ;A:0000 X:0009 Y:0001 D:0000 DB:01 S:01F2 P:envMXdiZCHC:0314 VC:251 00 FL:5379
			SBC $14D4,x             ;A:0000 X:0009 Y:0001 D:0000 DB:01 S:01F3 P:eNVMXdizcHC:0342 VC:251 00 FL:5379
			STA $00                 ;A:00FF X:0009 Y:0001 D:0000 DB:01 S:01F3 P:eNvMXdizcHC:0374 VC:251 00 FL:5379
			LDY $01                 ;A:00FF X:0009 Y:0001 D:0000 DB:01 S:01F3 P:eNvMXdizcHC:0398 VC:251 00 FL:5379
			BEQ SPR_L38             ;A:00FF X:0009 Y:0001 D:0000 DB:01 S:01F3 P:envMXdizcHC:0422 VC:251 00 FL:5379
			EOR #$80                ;A:00FF X:0009 Y:0001 D:0000 DB:01 S:01F3 P:envMXdizcHC:0438 VC:251 00 FL:5379
			STA $00                 ;A:007F X:0009 Y:0001 D:0000 DB:01 S:01F3 P:envMXdizcHC:0454 VC:251 00 FL:5379
SPR_L38:             LDA $00                 ;A:007F X:0009 Y:0001 D:0000 DB:01 S:01F3 P:envMXdizcHC:0478 VC:251 00 FL:5379
			BPL RETURN_35           ;A:007F X:0009 Y:0001 D:0000 DB:01 S:01F3 P:envMXdizcHC:0502 VC:251 00 FL:5379
			BMI ERASE_SPRITE        ;A:8AFF X:0002 Y:0000 D:0000 DB:01 S:01F3 P:eNvMXdizcHC:0704 VC:184 00 FL:5490

SUB_IS_OFF_SCREEN:   LDA !H_OFFSCREEN,x       ; \ if sprite is on screen, accumulator = 0
			ORA !V_OFFSCREEN,x       ; |
			RTS			 ; / RETURN


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; GET_DRAW_INFO
; This is a helper for the graphics routine.  It sets off screen flags, and sets up
; variables.  It will RETURN with the following:
;
;		Y = index to sprite OAM ($300)
;		$00 = sprite x position relative to screen boarder
;		$01 = sprite y position relative to screen boarder
;
; It is adapted from the subroutine at $03B760
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

SPR_T1:              db $0C,$1C
SPR_T2:              db $01,$02

GET_DRAW_INFO:       STZ !V_OFFSCREEN,x       ; reset sprite offscreen flag, vertical
			STZ !H_OFFSCREEN,x       ; reset sprite offscreen flag, horizontal
			LDA $E4,x               ; \
			CMP $1A                 ;  | set horizontal offscreen if necessary
			LDA $14E0,x             ;  |
			SBC $1B                 ;  |
			BEQ ON_SCREEN_X         ;  |
			INC !H_OFFSCREEN,x       ; /

ON_SCREEN_X:         LDA $14E0,x             ; \
			XBA			 ;  |
			LDA $E4,x               ;  |
			REP #$20                ;  |
			SEC			 ;  |
			SBC $1A                 ;  | mark sprite INVALID if far enough off screen
			CLC			 ;  |
			ADC.w #$0040            ;  |
			CMP.w #$0180            ;  |
			SEP #$20                ;  |
			ROL A                   ;  |
			AND #$01                ;  |
			STA $15C4,x             ; /
			BNE INVALID             ;

			LDY #$00                ; \ set up loop:
			LDA $1662,x             ;  |
			AND #$20                ;  | if not smushed (1662 & 0x20), go through loop twice
			BEQ ON_SCREEN_LOOP      ;  | else, go through loop once
			INY			 ; /
ON_SCREEN_LOOP:      LDA !SPRITE_Y_POS,x               ; \
			CLC			 ;  | set vertical offscreen if necessary
			ADC SPR_T1,y            ;  |
			PHP			 ;  |
			CMP $1C                 ;  | (vert screen boundry)
			ROL $00                 ;  |
			PLP			 ;  |
			LDA $14D4,x             ;  |
			ADC #$00                ;  |
			LSR $00                 ;  |
			SBC $1D                 ;  |
			BEQ ON_SCREEN_Y         ;  |
			LDA !V_OFFSCREEN,x       ;  | (vert offscreen)
			ORA SPR_T2,y            ;  |
			STA !V_OFFSCREEN,x       ;  |
ON_SCREEN_Y:         DEY			 ;  |
			BPL ON_SCREEN_LOOP      ; /

			LDY $15EA,x             ; get offset to sprite OAM
			LDA $E4,x               ; \
			SEC			 ;  |
			SBC $1A                 ;  | $00 = sprite x position relative to screen boarder
			STA $00                 ; /
			LDA !SPRITE_Y_POS,x               ; \
			SEC			 ;  |
			SBC $1C                 ;  | $01 = sprite y position relative to screen boarder
			STA $01                 ; /
			RTS			 ; RETURN

INVALID:             PLA			 ; \ RETURN from *main gfx routine* subroutine...
			PLA			 ;  |    ...(not just this subroutine)
			RTS			 ; /