BATTLESNAKE battlesnake.s

    .include KAPE_GPU.i

ZP_PATTERN_INDEX = $00
ZP_ADDRESS = $01

INPUT_MASK_P1_UP    = 0b00010000
INPUT_MASK_P1_DOWN  = 0b01000000
INPUT_MASK_P1_LEFT  = 0b10000000
INPUT_MASK_P1_RIGHT = 0b00100000

INPUT_MASK_P2_UP    = 0b00000001
INPUT_MASK_P2_DOWN  = 0b00000100
INPUT_MASK_P2_LEFT  = 0b00001000
INPUT_MASK_P2_RIGHT = 0b00000010

    .byte   $00
    .org    $0300

_main:
    jmp start

; load spritesheets here
spritesheet:
    .incbin Data\spritesheet.bin

inputState:
    .byte 0

player1:
    .id: .byte 0            ; changes to $20 if golden (10xxxx)
    .head_x: .byte 15
    .head_y: .byte 4
    .tail_x: .byte 16
    .tail_y: .byte 4
    .gold_left: .word 0     ; 16bit how many frames left for golden battlesnake
    .last_head_direction: .byte %10
    .last_tail_direction: .byte 0

player2:
    .id: .byte $10            ; changes to $30 if golden (10xxxx)
    .head_x: .byte 15
    .head_y: .byte 4
    .tail_x: .byte 16
    .tail_y: .byte 4
    .gold_left: .word 0     ; 16bit how many frames left for golden battlesnake
    .last_head_direction: .byte 0
    .last_tail_direction: .byte 0

; include the rest of the code
    .include sendpatterntable.s
    .include player.s

start:
    lda #0
    sta inputState

; set GPU to graphics mode
    lda #CF_CMD_SETMODE_GRAPHICS
    sta GPU_CMDQ_ADDRESS

    lda #$ff
    jsr GPU_ClearScreenA

    lda #<spritesheet
    sta ZP_ADDRESS
    lda #>spritesheet
    sta ZP_ADDRESS+1
    jsr sendpatterntable


; register input read interrupt
    lda #<handleInput
    sta INT_Vectors
    lda #>handleInput
    sta INT_Vectors+1

; send which player we are refering to
    lda #<player1
    sta ZP_ADDRESS
    lda #>player1
    sta ZP_ADDRESS+1

; write head and tail start positions to playfield (and screen)
    lda #%10
    sta tmpDirection
    jsr writeHead
    jsr writeTail

loop:
    jsr checkInput
    inc .frameCounter
    lda .frameCounter
    cmp #7
    bne .skipReset
    lda 0
    sta .frameCounter
    jsr moveHead
    jsr moveTail
    .skipReset:
    jsr ROM_WaitForVBlank

    jmp loop

    .frameCounter:
    .byte 0

checkInput:
    lda inputState
    bne .start
    rts

    .oppositeDirection:
    .byte $00
    .start:
    ; player 1
    lda #<player1
    sta ZP_ADDRESS
    lda #>player1
    sta ZP_ADDRESS+1
    ldy #7
    lda (ZP_ADDRESS),Y
    clc
    adc #2 ; opposite direction is always +-2
    and #%11 ; get only direction
    sta .oppositeDirection
    ; check up
    lda inputState
    and #INPUT_MASK_P1_UP
    beq .checkP1Down
    lda #3
    cmp .oppositeDirection
    beq .checkP2
    jmp .writeP1Head
    .checkP1Down:
    lda inputState
    and #INPUT_MASK_P1_DOWN
    beq .checkP1Left
    lda #1
    cmp .oppositeDirection
    beq .checkP2
    jmp .writeP1Head
    .checkP1Left:
    lda inputState
    and #INPUT_MASK_P1_LEFT
    beq .checkP1Right
    lda #2
    cmp .oppositeDirection
    beq .checkP2
    jmp .writeP1Head
    .checkP1Right:
    lda inputState
    and #INPUT_MASK_P1_RIGHT
    beq .checkP2
    lda #0
    cmp .oppositeDirection
    beq .checkP2
    .writeP1Head:
    sta tmpDirection
    ; write new head
    jsr writeHead
    rts
    .checkP2:
    ;TODO: Add Player 2 input checks
    rts

handleInput:
    lda PC_READ_ADDRESS
    beq .skipInput ; skip if 0 to make sure we catch all
    sta inputState
    .skipInput:
    jmp INT_Return

    .include KAPE_GPU.s
    .include KAPE_ROM.s