dmgtris/src/field.asm

IF !DEF(FIELD_ASM)
DEF FIELD_ASM EQU 1


INCLUDE "globals.asm"


SECTION "Field Variables", WRAM0
wField:: ds (10*21)


SECTION "Field Functions", ROM0
FieldInit::
    ld hl, wField
    ld bc, 10*21
    ld d, 1
    call UnsafeMemSet
    ret


FieldClear::
    ld hl, wField
    ld bc, 10*21
    ld d, TILE_FIELD_EMPTY
    call UnsafeMemSet
    ret

    ; This routine will copy wField onto the screen.
BlitField::
    ; What to copy
    ld de, wField + 10
    ; Where to put it
    ld hl, FIELD_TOP_LEFT
    ; How much to increment hl after each row
    ld bc, 32-10

    ; The first 14 rows can be blitted without checking for vram access.
    REPT 14
        REPT 10
            ld a, [de]
            ld [hl+], a
            inc de
        ENDR
        add hl, bc
    ENDR

:   ldh a, [rLY]
    cp a, 0
    jr nz, :-

    ; The last 6 rows need some care.
    REPT 6
        ; Wait until start of drawing, then insert 35 nops.
:       ldh a, [rSTAT]
        and a, 3
        cp a, 3
        jr nz, :-
        REPT 35
            nop
        ENDR

        ; Blit a line.
        REPT 10
            ld a, [de]
            ld [hl+], a
            inc de
        ENDR

        ; Increment HL so that the next line can be blitted.
        add hl, bc
    ENDR

    ; This has to finish just before the first LCDC interrupt of the frame or stuff will break in weird ways.
    jp EventLoop


ENDC