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05_best_sprite_moves.asm
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05_best_sprite_moves.asm
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include "gbhw.inc"
include "dma.inc" ; allows us to use dma_Copy2HRAM macro
include "sprite.inc" ; gives us spr_* macros to modify all sprites
;-------------- INTERRUPT VECTORS ------------------------
; specific memory addresses are called when a hardware interrupt triggers
; Vertical-blank triggers each time the screen finishes drawing. Video-RAM
; (VRAM) is only available during VBLANK. So this is when updating OAM /
; sprites is executed.
SECTION "Vblank", ROM0[$0040]
JP DMA_ROUTINE
SECTION "LCDC", ROM0[$0048]
reti
SECTION "Timer", ROM0[$0050]
reti
SECTION "Serial", ROM0[$0058]
reti
SECTION "Joypad", ROM0[$0060]
reti
;----------- END INTERRUPT VECTORS -------------------
SECTION "ROM_entry_point", ROM0[$0100] ; ROM is given control from boot here
nop
jp code_begins
;------------- BEGIN ROM HEADER ----------------
; The gameboy reads this info (before handing control over to ROM)
SECTION "rom header", ROM0[$0104]
NINTENDO_LOGO
ROM_HEADER "macro and dma "
; here's where you can include additional .asm modules
include "memory.asm"
SpriteAttr copyright ; declare "copyright" as a sprite
code_begins:
di ; disable interrupts
ld SP, $FFFF ; set stack to top of HRAM
dma_Copy2HRAM ; sets up routine from dma.inc that updates sprites
ld a, IEF_VBLANK ; --
ld [rIE], a ; Set only Vblank interrupt flag
ei ; enable interrupts. Only vblank will trigger
ld a, [rLCDC] ; fetch LCD Config. (Each bit is a flag)
or LCDCF_OBJON ; enable sprites through "OBJects ON" flag
or LCDCF_OBJ8 ; enable 8bit wide sprites (vs. 16-bit wide)
ld [rLCDC], a ; save LCD Config. Sprites are now visible.
; don't need to wait for vblank since DMA_routine is now called
; automatically when that happens
; ----
; DMA_ROUTINE is called each vblank now handles moving data data starting at
; _RAM ($C000) into $FE00. So now we write sprite data at $C000
; There are a total of 40 sprites available to manipulate.
; Each sprite has 4 attributes that are set in sequential bytes in memory:
; X coordinate
; Y coordinate
; Tile # (relative to start of tiles in VRAM: $8000)
; Sprite Flags (such as, visible, priority, X & Y flip)
; see where we declare "copyright" as a sprite-variable above
; set X=20, Y=10, Tile=$19, Flags=0
PutSpriteXAddr copyright, 20
PutSpriteYAddr copyright, 10
sprite_PutTile copyright, $19
sprite_PutFlags copyright, $00
.loop
halt ; halts cpu until interrupt triggers (vblank)
; by halting, we ensure that .loop only runs only each screen-refresh,
; so only 60fps. That makes the sprite movement here manageable
nop
; move copyright symbol diagonally across screen
GetSpriteXAddr copyright
inc A
PutSpriteXAddr copyright, A
GetSpriteYAddr copyright ; macro GetSpr... puts Y value in A register
inc A
PutSpriteYAddr copyright, A
jp .loop ; start up at top of .loop label. Repeats each vblank