;
; example.asm for TR8
;
.org 0

; address of the frame interrupt vector
.equ INT_VECT 0xff00

    ; setup an int handler so we
    ; can use the frame int to sync
    ld a, >INT_VECT
    ld x, <INT_VECT
    ld b, <int_handler
    ld [a : x], b
    inc x
    ld b, >int_handler
    ld [a : x], b

    ; enable interrupts
    cif

    ; loop filling the screen with one
    ; colour cycling the whole palette
    ld b, 0
loop:
    call fill
    inc b
    and b, 15

    push b
    call draw_sprite
    pop b

    ; wait 1 second
    ld x, 60
wait_loop:
    halt
    dec x
    bnz
    jmp wait_loop

    jmp loop

    ; fill frame-buffer with a color in reg b
fill:
    ld a, 0xbf
    ld x, 0
    ld y, 0x40
fill_loop:
    ld [a : x], b
    inc x
    bno
    jmp fill_loop
    inc a
    dec y
    bnz
    jmp fill_loop
    ret

int_handler:
    iret

draw_sprite:
    push y
    ld y, 16
    ld [sp + 0], y

    ; src
    ld a, >sprite
    ld x, <sprite

    ; dst
    ld b, 0xdb
    ld y, 56
line:
    push x
    ld x, [a : x]

    ; any color with index > 15
    ; is transparent
    cmp x, 16
    bnc
    jmp transparent

    ld [b : y], x

transparent:
    pop x

    inc x
    bo
    inc a

    inc y

    push y
    ld y, [sp + 1]
    dec y
    ld [sp + 1], y
    pop y

    bnz
    jmp line

    add y, 112
    bo
    inc b

    cmp x, <end_sprite
    bnz
    jmp next_row
    cmp a, >end_sprite
    bz
    jmp done

next_row:
    push y
    ld y, 16
    ld [sp + 1], y
    pop y

    jmp line

done:
    pop y
    ret

sprite:
    .incpng "assets/icon.png"
end_sprite: