island-story/src/map.s

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

SECTION "Map Data", WRAM0

PAGEX:: DB
PAGEY:: DB

CURRENT_DATA_START::
CURRENT_TILE_PTR:: DW
CURRENT_TILE_SIZE:: DB
CURRENT_MAP_PTR:: DW
CURRENT_MAP_COLLISION:: DW
CURRENT_MAP_WIDTH:: DB
CURRENT_MAP_HEIGHT:: DB
CURRENT_SPAWN_X:: DB
CURRENT_SPAWN_Y:: DB
CURRENT_CAMERA_X:: DB
CURRENT_CAMERA_Y:: DB
CURRENT_DATA_END::

SECTION "Map Code", ROM0

DEF INIT_SCX EQUS "((SCRN_VX - SCRN_X) / 2)"
DEF INIT_SCY EQUS "((SCRN_VY - SCRN_Y) / 2)"

DEF PAGE_SIZE EQU 2

DEF STACK_OFFSET_ROW EQU 3
DEF STACK_OFFSET_MAP EQU 1
DEF STACK_OFFSET_LEFT EQU 0

; TODO: Don't hardcode
DEF CAMERAX EQU 0
DEF CAMERAY EQU 14

; Increments a 16-bit value located on the stack
; \1 Stack offset
MACRO INC_STACK16
    ld hl, sp + \1
    inc [hl]
    jr nz, .no_carry\@

    inc hl
    inc [hl]

.no_carry\@:
ENDM

MACRO ZERO_ROW_TILE
    ld hl, sp + STACK_OFFSET_ROW
    ld a, [hl+]
    ld e, a
    ld d, [hl]
    xor a
    ld [de], a
ENDM

; Loads a map
; @param hl Pointer to map metadata
Map_Load::
    ; Initialize scroll state
    ld a, INIT_SCX
    ld [rSCX], a

    ld a, INIT_SCY
    ld [rSCY], a

    xor a
    ld [PAGEX], a
    ld [PAGEY], a

    ; Store metadata
    ld bc, CURRENT_DATA_START
    ld d, CURRENT_DATA_END - CURRENT_DATA_START
    call memcpy

    ; Write tiles to VRAM
    ld hl, CURRENT_TILE_PTR
    ld a, [hl+]
    ld c, a
    ld a, [hl+]
    ld b, a

    ld a, [CURRENT_TILE_SIZE]
    ld d, a

    ld hl, _VRAM
    MEMCPY hl, bc, d

    ; Write initial map data
    ld hl, _SCRN0

    ld a, [CURRENT_CAMERA_X]
    sub INIT_SCX / 8
    ld b, a

    ld a, [CURRENT_CAMERA_Y]
    sub INIT_SCY / 8
    ld c, a

    ld d, SCRN_VY_B
.write_rows:
    call write_map_row
    inc c
    dec d
    jr nz, .write_rows

    ret

; Write a row of map data into map RAM
; @param b Map X coordinate (signed)
; @param c Map Y coordinate (signed)
; @param hl Start of the row to write
write_map_row:
    push bc ; sp + 7
    push de ; sp + 5
    push hl ; sp + 3

    ; If Y < 0, write a row of 0s
    bit 7, c
    jr nz, .zero_row

    ; If Y >= MAP_HEIGHT, write a row of 0s
    ld a, [CURRENT_MAP_HEIGHT]
    dec a
    cp c
    jr nc, .begin_writing

.zero_row:
    ld d, SCRN_VX_B
    xor a
.zero_row_loop:
    ld a, [hl+]
    dec d
    jr nz, .zero_row_loop
.zero_row_done:
    pop hl
    pop de
    pop bc
    ret

.begin_writing:
    ; Allocate 2 bytes for map pointer
    ; Allocate 1 byte for number of tiles left
    add sp, -3

    ; left = number of tiles left to write
    ld hl, sp + STACK_OFFSET_LEFT
    ld [hl], SCRN_VX_B

    ; HL = CURRENT_MAP_PTR + Y * CURRENT_MAP_HEIGHT
    ld a, [CURRENT_MAP_PTR]
    ld l, a
    ld a, [CURRENT_MAP_PTR + 1]
    ld h, a

.compute_map_row:
    ld a, c
    or a
    jr z, .compute_map_row_done

    ld a, [CURRENT_MAP_HEIGHT]
    ADD16 HL
    dec c
    jr .compute_map_row

    ; map = HL
.compute_map_row_done:
    LD16 de, hl
    ld hl, sp + STACK_OFFSET_MAP
    ld a, e
    ld [hl+], a
    ld a, d
    ld [hl], a

    ld hl, sp + STACK_OFFSET_LEFT

    ; While X < 0 and left > 0, write 0 to the row
.pad_left:
    bit 7, b
    jr z, .copy_center

    ld a, [hl]
    or a
    jr z, .done

    ; *row = 0
    ZERO_ROW_TILE

    ; row++
    INC_STACK16 STACK_OFFSET_ROW

    ; X++, left--
    inc b
    ld hl, sp + STACK_OFFSET_LEFT
    dec [hl]
    jr .pad_left

    ; While X < MAP_WIDTH and [SP] > 0, copy from map
.copy_center:
    ld a, [CURRENT_MAP_WIDTH]
    dec a
    cp b
    jr z, .pad_right

    ld a, [hl]
    or a
    jr z, .done

    ; A = *map_ptr
    ld hl, sp + STACK_OFFSET_MAP
    ld a, [hl+]
    ld e, a
    ld d, [hl]
    ld a, [de]

    ; map_ptr++
    INC_STACK16 STACK_OFFSET_MAP

    ; *row = A
    ld hl, sp + STACK_OFFSET_ROW
    ld e, [hl]
    inc hl
    ld d, [hl]
    ld [de], a

    ; row++
    INC_STACK16 3

    ; X++, [SP]--
.copy_center_inc:
    inc b
    ld hl, sp + STACK_OFFSET_LEFT
    dec [hl]
    jr .copy_center

    ; While [SP] > 0, write 0 to the row
.pad_right:
    ld a, [hl]
    or a
    jr z, .done

    ; *row = 0
    ZERO_ROW_TILE

    ; row++
    INC_STACK16 STACK_OFFSET_ROW

    ; [SP]--
.pad_right_inc:
    ld hl, sp + STACK_OFFSET_ROW
    dec [hl]
    jr .pad_right

.done:
    add sp, 3
    pop hl
    pop de
    pop bc

    ret