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Add enemy ships.

main
Colin McMillen 6 years ago
parent
commit
d460a519af
  1. 6
      memory.asm
  2. 116
      pewpew.asm

6
memory.asm

@ -15,6 +15,8 @@
; 0040-009F: {sprite, x, y, x-velocity, y-velocity, unused} per player shot.
; If sprite is 0, the shot is disabled.
; 00A0-015F: As above, for enemy shots.
; 0160-????: {sprite, x, y, move AI type, shoot AI type, shot cooldown}
; per enemy ship.
; [gap]
; Sprite table buffers -- copied each frame to OAM during VBlank, using DMA.
; 1000-11FF: table 1 (4 bytes each: x/y coord, tile #, flip/priority/palette)
@ -38,6 +40,10 @@
.define enemyShotArray $A0
.define enemyShotArrayLength 32
.define shotSize 6
.define enemyShipArray $160
.define enemyShipArrayLength 4
.define enemyShipSize 6
.define numSprites 128
.define spriteTableStart $1000

116
pewpew.asm

@ -471,7 +471,9 @@ MaybeShootDone:
UpdateWorld:
jsr UpdateShotCooldown
jsr SpawnEnemyShips
jsr SpawnEnemyShots
jsr UpdateEnemyShips
jsr UpdateShotPositions
jsr CheckCollisionsWithPlayer
jsr UpdateBackgroundScroll
@ -491,12 +493,86 @@ UpdateShotCooldown:
SpawnEnemyShips:
GetRandomByte
bit #%00111111 ; Spawn ships every this-many frames (on average).
beq +
rts
+
; Find an empty spot in the array.
ldy #0
-
lda enemyShipArray, Y
cmp #0
beq +
.rept enemyShipSize
iny
.endr
cpy #(enemyShipArrayLength * enemyShipSize)
bne -
rts ; Too many ships; bail.
+
lda #4 ; Sprite number.
sta enemyShipArray, Y
lda #(256 - 32)
sta enemyShipArray + 1, Y ; x.
-
GetRandomByte
cmp #(224 - 32)
bcs - ; Keep trying.
sta enemyShipArray + 2, Y ; y.
lda #0
sta enemyShipArray + 3, Y ; move AI type.
sta enemyShipArray + 4, Y ; shoot AI type.
lda #8
sta enemyShipArray + 5, Y ; shot cooldown.
rts
; TODO(mcmillen): reap ships if they move off the top, bottom, or right too.
UpdateEnemyShips:
ldy #0
--
lda enemyShipArray, Y
cmp #0
beq ++
lda enemyShipArray + 1, Y ; x
clc
adc #-2
bcs +
lda #0
sta enemyShipArray, Y ; reap it.
bra ++
+
sta enemyShipArray + 1, Y
++
.rept enemyShipSize
iny
.endr
cpy #(enemyShipArrayLength * enemyShipSize)
bne --
rts
SpawnEnemyShots:
lda vBlankCounter
bit #%00001111 ; Spawn shots every this-many frames.
beq +
rts
+
; Find an empty spot in the array.
ldy #0
-
lda enemyShotArray, Y
@ -604,7 +680,7 @@ ShotDone:
.rept shotSize
inx
.endr
cpx #(playerShotArrayLength * enemyShotArrayLength * shotSize)
cpx #((playerShotArrayLength + enemyShotArrayLength) * shotSize)
bne UpdateShot
rts
@ -699,7 +775,7 @@ UpdateBackgroundScroll:
UpdateSprites:
UpdateSprites: ; TODO(mcmillen): refactor into smaller pieces.
; This page is a good reference on SNES sprite formats:
; http://wiki.superfamicom.org/snes/show/SNES+Sprites
; It uses the same approach we're using, in which we keep a buffer of the
@ -745,6 +821,42 @@ UpdateSprites:
.endr
iny
; Now add enemy ships.
sty $00 ; Save sprite table 2 index.
ldy #0 ; Index into enemyShipArray.
-
lda enemyShipArray, Y
cmp #0 ; If not enabled, skip to next ship.
beq +
; Update sprite table 1.
sta spriteTableStart + 2, X ; sprite number
lda enemyShipArray + 1, Y
sta spriteTableStart, X ; x
lda enemyShipArray + 2, Y
sta spriteTableStart + 1, X ; y
lda #%01000000 ; flip horizontally.
sta spriteTableStart + 3, X
; Update secondary sprite table.
phy ; Save enemyShipArray index.
ldy $00
lda #%11000000 ; Enable large sprite.
sta spriteTableScratchStart, Y
iny
sty $00
ply ; Restore enemyShipArray index.
.rept 4
inx
.endr
+
.rept enemyShipSize
iny
.endr
cpy #(enemyShipArrayLength * enemyShipSize)
bne -
ldy $00 ; Restore Y to its rightful self.
; Now add shots.
sty $00 ; Save sprite table 2 index.
ldy #0 ; Index into playerShotArray.

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