island-story/src/bg.s

INCLUDE "hardware.inc"
INCLUDE "util.inc"

INCLUDE "png/map/intro.inc"

SECTION "BG Data", WRAM0

BG_COLLISION_DATA:: dw
BG_MAP_WIDTH:: db
BG_MAP_HEIGHT:: db

BG_SCROLLING:: db

SECTION "BG Code", ROM0

MACRO update_map_info
    ld hl, BG_COLLISION_DATA
    ld a, HIGH(\1)
    ld [hl+], a
    ld a, LOW(\1)
    ld [hl+], a

    ld a, \2
    ld [hl+], a

    ld a, \3
    ld [hl+], a
ENDM

BG_Init::
    SET8 BG_SCROLLING, 0

    ; copy map
    ld e, intro_HEIGHT
    ld bc, _SCRN0
    ld hl, intro_MAP
.copy_map_row:
    ld d, intro_WIDTH
    call memcpy
    dec e
    jr z, .done
    ; nothing to skip if map is max width
    ld a, 32 - intro_WIDTH
    or a
    jr z, .copy_map_row
    ld d, a
.skip:
    ; skip over trailing part in vram
    inc c
    jr nz, .nocarry
    inc b
.nocarry:
    dec d
    jr nz, .skip
    jr .copy_map_row
.done:

    ; copy tiles
    ld hl, intro_TILES
    ld bc, _VRAM
    ld d, intro_NUM_TILES
    call memcpy

    update_map_info intro_COLLISION, intro_WIDTH, intro_HEIGHT

    ret

BG_Update::
    ret