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Add shots that come from enemy ships.

main
Colin McMillen 6 years ago
parent
commit
08fae310e8
  1. 93
      pewpew.asm

93
pewpew.asm

@ -5,6 +5,10 @@
; TODO(mcmillen): define screen / ship / shot dimensions as constants.
; Sets A to 8-bit (& enables 8-bit "B" register).
.MACRO SetA8Bit
sep #%00100000 ; 8-bit A/B.
@ -471,10 +475,10 @@ MaybeShootDone:
UpdateWorld:
jsr UpdateShotCooldown
jsr UpdateShotPositions
jsr SpawnEnemyShips
jsr SpawnEnemyShots
jsr UpdateEnemyShips
jsr UpdateShotPositions
jsr CheckCollisionsWithPlayer
jsr UpdateBackgroundScroll
rts
@ -529,7 +533,7 @@ SpawnEnemyShips:
sta enemyShipArray + 3, Y ; move AI type.
sta enemyShipArray + 4, Y ; shoot AI type.
lda #8
lda #12
sta enemyShipArray + 5, Y ; shot cooldown.
rts
@ -539,14 +543,17 @@ SpawnEnemyShips:
; TODO(mcmillen): reap ships if they move off the top, bottom, or right too.
UpdateEnemyShips:
ldy #0
sty $00 ; Index into enemyShotArray.
--
lda enemyShipArray, Y
cmp #0
cmp #0 ; If it's not enabled, skip it.
beq ++
; Move the ship.
; TODO(mcmillen): implement different movement based on AI-type.
lda enemyShipArray + 1, Y ; x
clc
adc #-2
adc #-2 ; x-velocity.
bcs +
lda #0
sta enemyShipArray, Y ; reap it.
@ -554,8 +561,26 @@ UpdateEnemyShips:
+
sta enemyShipArray + 1, Y ; move it.
lda enemyShipArray + 5, Y ; shot cooldown
cmp #0
beq +
dec A
sta enemyShipArray + 5, Y ; new shot cooldown
bra ++
++
+ ; Add a shot.
; TODO(mcmillen): implement different shooting based on shoot-type.
lda enemyShipArray + 1, Y
sta $02 ; Enemy ship X.
lda enemyShipArray + 2, Y
sta $03 ; Enemy ship Y.
lda #12
sta enemyShipArray + 5, Y ; new shot cooldown
phy
jsr SpawnEnemyShot
ply
++ ; Done processing this ship.
.rept enemyShipSize
iny
.endr
@ -566,48 +591,52 @@ UpdateEnemyShips:
SpawnEnemyShots:
lda vBlankCounter
bit #%00011111 ; Spawn shots every this-many frames.
beq +
; Expects:
; $00: index into enemyShotArray (bytes).
; $02: enemy ship x-position.
; $03: enemy ship y-position.
;
; Modifies: A & Y.
; $00: new index into enemyShotArray (bytes).
SpawnEnemyShot:
ldy $00
-
; Bail if at end of array.
cpy #(enemyShotArrayLength * shotSize)
bne +
sty $00
rts
+
; Find an empty spot in the array.
ldy #0
-
lda enemyShotArray, Y
cmp #0
beq +
.rept 6
; Try next slot.
.rept shotSize
iny
.endr
cpy #(enemyShotArrayLength * shotSize)
bne -
rts ; Too many shots; bail.
bra -
+
; OK, found a spot.
lda #9 ; Sprite number.
sta enemyShotArray, Y
lda #254
sta enemyShotArray + 1, Y ; x.
lda $02 ; Get enemy x.
sta enemyShotArray + 1, Y ; Save as shot x.
lda #((224 - 32) / 2)
and #%01111111
sta enemyShotArray + 2, Y ; y.
lda $03 ; Get enemy y.
clc
adc #((32 - 4) / 2) ; Center it with enemy ship.
sta enemyShotArray + 2, Y ; Save as shot y.
lda #-4
lda #-6
sta enemyShotArray + 3, Y ; x-velocity.
GetRandomByte
and #%00000111 ; [0, 7]
clc
adc #-3 ; [-3, 4]
cmp #4
bne +
lda #0 ; [-3, 3] with 2x chance of zero.
+
lda #0
sta enemyShotArray + 4, Y ; y-velocity.
sty $00
rts

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