;;; $897B: Move enemy projectile vertically ;;;
{
;; Parameters:
;;     X: Enemy projectile index
;; Returns:
;;     Carry: Set if collided with block

; This routine expects:
;     Enemy projectile $1A6F: Y subposition
;     Enemy projectile $1ADB: Y velocity (unit 1/100h px/frame)
$86:897B DA          PHX
$86:897C 64 12       STZ $12    [$7E:0012]  ;\
$86:897E 64 14       STZ $14    [$7E:0014]  ;|
$86:8980 BD DB 1A    LDA $1ADB,x[$7E:1AFD]  ;|
$86:8983 10 02       BPL $02    [$8987]     ;} $14.$12 = [enemy projectile Y velocity] / 100h
$86:8985 C6 14       DEC $14    [$7E:0014]  ;|
                                            ;|
$86:8987 85 13       STA $13    [$7E:0013]  ;/
$86:8989 BD B4 1B    LDA $1BB4,x[$7E:1BD6]  ;\
$86:898C 29 FF 00    AND #$00FF             ;} $1E = [enemy projectile Y radius]
$86:898F 85 1E       STA $1E    [$7E:001E]  ;/
$86:8991 BD B3 1B    LDA $1BB3,x[$7E:1BD5]  ;\
$86:8994 29 FF 00    AND #$00FF             ;} $1C = [enemy projectile X radius]
$86:8997 85 1C       STA $1C    [$7E:001C]  ;/
$86:8999 BD 4B 1A    LDA $1A4B,x[$7E:1A6D]  ;\
$86:899C 38          SEC                    ;|
$86:899D E5 1C       SBC $1C    [$7E:001C]  ;|
$86:899F 29 F0 FF    AND #$FFF0             ;|
$86:89A2 85 1A       STA $1A    [$7E:001A]  ;|
$86:89A4 BD 4B 1A    LDA $1A4B,x[$7E:1A6D]  ;|
$86:89A7 18          CLC                    ;|
$86:89A8 65 1C       ADC $1C    [$7E:001C]  ;|
$86:89AA 3A          DEC A                  ;} $1A = (enemy projectile right boundary) / 10h - (enemy projectile left boundary) / 10h (number of blocks left to check)
$86:89AB 38          SEC                    ;|
$86:89AC E5 1A       SBC $1A    [$7E:001A]  ;|
$86:89AE 4A          LSR A                  ;|
$86:89AF 4A          LSR A                  ;|
$86:89B0 4A          LSR A                  ;|
$86:89B1 4A          LSR A                  ;|
$86:89B2 85 1A       STA $1A    [$7E:001A]  ;/
$86:89B4 85 20       STA $20    [$7E:0020]  ; $20 = [$1A] (enemy projectile X block span)
$86:89B6 BD 6F 1A    LDA $1A6F,x[$7E:1A91]  ;\
$86:89B9 18          CLC                    ;|
$86:89BA 65 12       ADC $12    [$7E:0012]  ;|
$86:89BC 85 16       STA $16    [$7E:0016]  ;} $18.$16 = [enemy projectile Y position] + [$14].[$12] (target position)
$86:89BE BD 93 1A    LDA $1A93,x[$7E:1AB5]  ;|
$86:89C1 65 14       ADC $14    [$7E:0014]  ;|
$86:89C3 85 18       STA $18    [$7E:0018]  ;/
$86:89C5 24 14       BIT $14    [$7E:0014]  ;\
$86:89C7 30 06       BMI $06    [$89CF]     ;} If [$14] >= 0: (moving down)
$86:89C9 18          CLC                    ;\
$86:89CA 65 1E       ADC $1E    [$7E:001E]  ;} $22 = [$18] + [enemy projectile Y radius] - 1 (target front boundary)
$86:89CC 3A          DEC A                  ;/
$86:89CD 80 03       BRA $03    [$89D2]
$86:89CF 38          SEC                    ;\ Else ([$14] < 0): (moving up)
$86:89D0 E5 1E       SBC $1E    [$7E:001E]  ;} $22 = [$18] - [enemy projectile Y radius] (target front boundary)
$86:89D2 85 22       STA $22    [$7E:0022]
$86:89D4 4A          LSR A                  ;\
$86:89D5 4A          LSR A                  ;|
$86:89D6 4A          LSR A                  ;|
$86:89D7 4A          LSR A                  ;|
$86:89D8 E2 20       SEP #$20               ;|
$86:89DA 8D 02 42    STA $4202              ;|
$86:89DD AD A5 07    LDA $07A5  [$7E:07A5]  ;|
$86:89E0 8D 03 42    STA $4203              ;|
$86:89E3 C2 20       REP #$20               ;|
$86:89E5 BD 4B 1A    LDA $1A4B,x[$7E:1A6D]  ;|
$86:89E8 38          SEC                    ;} X = ((enemy projectile front boundary) / 10h * [room width] + (enemy projectile left boundary) / 10h) * 2 (index of leftmost block to check)
$86:89E9 E5 1C       SBC $1C    [$7E:001C]  ;|
$86:89EB 4A          LSR A                  ;|
$86:89EC 4A          LSR A                  ;|
$86:89ED 4A          LSR A                  ;|
$86:89EE 4A          LSR A                  ;|
$86:89EF 18          CLC                    ;|
$86:89F0 6D 16 42    ADC $4216              ;|
$86:89F3 0A          ASL A                  ;|
$86:89F4 AA          TAX                    ;/
; LOOP
$86:89F5 20 9E 88    JSR $889E  [$86:889E]  ; Enemy projectile vertical block reaction
$86:89F8 B0 13       BCS $13    [$8A0D]     ; If solid: go to BRANCH_SOLID
$86:89FA E8          INX                    ;\
$86:89FB E8          INX                    ;} X += 2
$86:89FC C6 1A       DEC $1A    [$7E:001A]  ; Decrement $1A
$86:89FE 10 F5       BPL $F5    [$89F5]     ; If [$1A] >= 0: go to LOOP
$86:8A00 FA          PLX
$86:8A01 A5 16       LDA $16    [$7E:0016]  ;\
$86:8A03 9D 6F 1A    STA $1A6F,x[$7E:1A91]  ;|
$86:8A06 A5 18       LDA $18    [$7E:0018]  ;} Enemy projectile Y position = [$18].[$16]
$86:8A08 9D 93 1A    STA $1A93,x[$7E:1AB5]  ;/
$86:8A0B 18          CLC                    ;\
$86:8A0C 60          RTS                    ;} Return carry clear
; BRANCH_SOLID
$86:8A0D FA          PLX
$86:8A0E 9E 6F 1A    STZ $1A6F,x[$7E:1A91]  ; Enemy projectile Y subposition = 0
$86:8A11 A5 22       LDA $22    [$7E:0022]
$86:8A13 24 14       BIT $14    [$7E:0014]  ;\
$86:8A15 30 10       BMI $10    [$8A27]     ;} If [$14] < 0: go to BRANCH_MOVING_UP
$86:8A17 29 F0 FF    AND #$FFF0             ; A = [$22] - [$22] % 10h (target bottom boundary rounded down to top of 16x16 tile)
$86:8A1A 38          SEC                    ;\
$86:8A1B E5 1E       SBC $1E    [$7E:001E]  ;|
$86:8A1D DD 93 1A    CMP $1A93,x[$7E:1AB5]  ;} Enemy projectile Y position = max([enemy projectile Y position], [A] - [enemy projectile Y radius])
$86:8A20 90 03       BCC $03    [$8A25]     ;|
$86:8A22 9D 93 1A    STA $1A93,x[$7E:1AB5]  ;/
$86:8A25 38          SEC                    ;\
$86:8A26 60          RTS                    ;} Return carry set
; BRANCH_MOVING_UP
$86:8A27 09 0F 00    ORA #$000F             ;\
$86:8A2A 38          SEC                    ;} A = [$22] - [$22] % 10h + 10h (target right boundary rounded up to bottom of 16x16 tile)
$86:8A2B 65 1E       ADC $1E    [$7E:001E]  ;\
$86:8A2D DD 93 1A    CMP $1A93,x[$7E:1AB3]  ;|
$86:8A30 F0 02       BEQ $02    [$8A34]     ;} Enemy projectile Y position = min([enemy projectile Y position], [A] + [enemy projectile Y radius])
$86:8A32 B0 03       BCS $03    [$8A37]     ;|
                                            ;|
$86:8A34 9D 93 1A    STA $1A93,x[$7E:1AB3]  ;/
$86:8A37 38          SEC                    ;\
$86:8A38 60          RTS                    ;} Return carry set
}
}