Battlesnakes ASM

; whenever calling player.s functions, put the player struct address for the player we are manipulating in the
; ZP_ADDRESS

    .local playfield

playfield:
    .repeat 768
    .byte 0
    .endrepeat

playfield_offset:
    .word $0000

playerAddress:
    .word $00

tempSpriteIndex:
    .byte $00

; write the players head to playfield and also draw to screen
writeHead:
    jsr savePlayerAddress

    lda #$0
    sta playfield_offset
    sta playfield_offset+1

    ldy #$0
    lda (ZP_ADDRESS), Y     ; get id and save to stack
    ; form the correct sprite index
    ; in the form of 00gpbbdd where
    ; gp - is a combined player id from having gold, and player id (saved in stack in this case)
    ; bb - is body part 0 - head, 1 - straight, 2 - bend, 3 - tail
    ; dd - is forwards direction 0 - right, 1 - down, 2 - left, 3 - up
    ; in this case, bb is 0 and we'll assume direction is left (0b10)
    ; and we just got the id, OR 0b10 with ID and save to stack
    ora #%10
    sta gpuIndex

    iny
    ; send set index command with proper arguments to GPU
    lda (ZP_ADDRESS), Y     ; get head_x
    sta gpuX
    sta playfield_offset+1  ; save x to playfield_offset
    iny
    lda (ZP_ADDRESS), Y     ; get head_y
    sta gpuY

    ldy #32
    jsr ROM_mul8x8 ; multiply A * Y (or head_y * 32)
    clc
    adc playfield_offset+1
    sta playfield_offset+1
    tya
    sta playfield_offset        ; save 32 (width) times Y added to X in playfield offset

    clc                         ; add playfield baseaddress to playfield offset to get absolute address in playfield_offset
    lda #<playfield
    adc playfield_offset+1
    sta ZP_ADDRESS      ; save in ZP_ADDRESS
    lda #>playfield
    adc playfield_offset
    sta ZP_ADDRESS+1

    lda gpuIndex
    sta (ZP_ADDRESS),Y
    jsr gpuSetIndex

    jsr loadPlayerAddress

    rts

writeTail:
    jsr savePlayerAddress

    ldy #$0
    lda (ZP_ADDRESS), Y     ; get id and save to stack
    ; form the correct sprite index
    ; in the form of 00gpbbdd where
    ; gp - is a combined player id from having gold, and player id (saved in stack in this case)
    ; bb - is body part 0 - head, 1 - straight, 2 - bend, 3 - tail
    ; dd - is forwards direction 0 - right, 1 - down, 2 - left, 3 - up
    ; in this case, bb is 3 (0b11) and we'll assume direction is 2 or left (0b10)
    ; let's OR the id in A with 0b1111 to get the proper sprite index
    ; and save it to stack
    ora #%1110
    sta gpuIndex
    ldy #3
    ; send set index command with proper arguments to GPU
    lda (ZP_ADDRESS), Y     ; get tail_x
    sta gpuX
    sta playfield_offset+1  ; save x to playfield_offset
    iny
    lda (ZP_ADDRESS), Y     ; get tail_y
    sta gpuY

    ldy #32
    jsr ROM_mul8x8 ; multiply A * Y (or tail_y * 32)
    clc
    adc playfield_offset+1
    sta playfield_offset+1
    tya
    sta playfield_offset        ; save 32 (width) times Y added to X in playfield offset

    clc                         ; add playfield baseaddress to playfield offset to get absolute address in playfield_offset
    lda #<playfield
    adc playfield_offset+1
    sta ZP_ADDRESS      ; save in ZP_ADDRESS
    lda #>playfield
    adc playfield_offset
    sta ZP_ADDRESS+1

    lda gpuIndex
    sta (ZP_ADDRESS),Y
    jsr gpuSetIndex

    jsr loadPlayerAddress
    rts

moveHead:
    jsr savePlayerAddress

    ; get player id and save to stack
    ; get player data at head location
    ldy #1
    lda (ZP_ADDRESS), Y     ; get head_x
    sta gpuX
    sta playfield_offset+1  ; save x to playfield_offset
    iny
    lda (ZP_ADDRESS), Y     ; get head_y
    sta gpuY
    ldy #32
    jsr ROM_mul8x8 ; multiply A * Y (or head_y * 32)

    clc
    adc playfield_offset+1
    sta playfield_offset+1
    tya
    sta playfield_offset        ; save 32 (width) times Y added to X in playfield offset

    clc                         ; add playfield baseaddress to playfield offset to get absolute address in playfield_offset
    lda #<playfield
    adc playfield_offset+1
    sta ZP_ADDRESS
    lda #>playfield
    adc playfield_offset
    sta ZP_ADDRESS+1

    ldy #0
    lda (ZP_ADDRESS),Y
    ; change spriteindex to be a straight part
    and #%11110011
    ora #%00000100
    sta (ZP_ADDRESS),Y
    sta gpuIndex
    jsr gpuSetIndex
    lda gpuIndex

    and #%11   ; And the direction
    beq moveHeadRight
    cmp #01
    beq moveHeadDown
    cmp #02
    beq moveHeadLeft

    ; move head up
    ; TODO: add code
    jsr loadPlayerAddress
    rts

  moveHeadRight:
    ; TODO: add code
    jsr loadPlayerAddress
    rts

  moveHeadDown:
    ; TODO: add code
    jsr loadPlayerAddress
    rts

  moveHeadLeft:
    jsr loadPlayerAddress

    ldy #1
    lda (ZP_ADDRESS),Y ; read X
    sec
    sbc #1
    and #%11111     ; scrap carry, ie. % 32
    sta (ZP_ADDRESS),Y  ; save new X

    jsr loadPlayerAddress

    jsr writeHead

    rts

moveTail:
    jsr savePlayerAddress

    ; get player id and save to stack
    ; get player data at tail location
    ldy #3
    lda (ZP_ADDRESS), Y     ; get tail_x
    sta playfield_offset+1  ; save x to playfield_offset
    iny
    lda (ZP_ADDRESS), Y     ; get tail_y
    ldy #32
    jsr ROM_mul8x8 ; multiply A * Y (or tail_y * 32)

    clc
    adc playfield_offset+1
    sta playfield_offset+1
    tya
    sta playfield_offset        ; save 32 (width) times Y added to X in playfield offset

    clc                         ; add playfield baseaddress to playfield offset to get absolute address in playfield_offset
    lda #<playfield
    adc playfield_offset+1
    sta ZP_ADDRESS
    lda #>playfield
    adc playfield_offset
    sta ZP_ADDRESS+1

    ldy #0
    lda (ZP_ADDRESS),Y
    pha
    lda #$ff
    sta (ZP_ADDRESS),Y
    pla

    and #%11   ; And the direction
    beq moveTailRight
    cmp #01
    beq moveTailDown
    cmp #02
    beq moveTailLeft

    ; move tail up
    ; TODO: add code
    jsr loadPlayerAddress
    rts

  moveTailRight:
    ; TODO: add code
    jsr loadPlayerAddress
    rts

  moveTailDown:
    ; TODO: add code
    jsr loadPlayerAddress
    rts

  moveTailLeft:
    lda #$ff
    sta (ZP_ADDRESS), Y
    sta gpuIndex

    jsr loadPlayerAddress

    ldy #3
    lda (ZP_ADDRESS), Y     ; get tail_x
    sta gpuX
    iny
    lda (ZP_ADDRESS), Y     ; get tail_y
    sta gpuY

    jsr gpuSetIndex

    jsr loadPlayerAddress

    ldy #3
    lda (ZP_ADDRESS), Y     ; get tail_x
    sec
    sbc #1
    and #%11111     ; scrap carry, ie. % 32
    sta (ZP_ADDRESS), Y     ; save new head_x

    jsr loadPlayerAddress

    jsr writeTail

    rts

loadPlayerAddress:
    lda playerAddress
    sta ZP_ADDRESS
    lda playerAddress+1
    sta ZP_ADDRESS+1
    rts

savePlayerAddress:
    lda ZP_ADDRESS
    sta playerAddress
    lda ZP_ADDRESS+1
    sta playerAddress+1
    rts

gpuX:
    .byte $00
gpuY:
    .byte $00
gpuIndex:
    .byte $00

gpuSetIndex:
    lda #CF_CMD_SET_INDEX
    sta GPU_CMDQ_ADDRESS
    lda gpuX
    sta GPU_CMDQ_ADDRESS
    lda gpuY
    sta GPU_CMDQ_ADDRESS
    lda gpuIndex
    sta GPU_CMDQ_ADDRESS

    rts