1 files changed, 189 insertions, 0 deletions
diff --git a/engine/gfx/sprite_oam.asm b/engine/gfx/sprite_oam.asm
new file mode 100644
index 00000000..68128413
--- /dev/null
+++ b/engine/gfx/sprite_oam.asm
@@ -0,0 +1,189 @@
+PrepareOAMData::
+; Determine OAM data for currently visible
+; sprites and write it to wOAMBuffer.
+
+	ld a, [wUpdateSpritesEnabled]
+	dec a
+	jr z, .updateEnabled
+
+	cp -1
+	ret nz
+	ld [wUpdateSpritesEnabled], a
+	jp HideSprites
+
+.updateEnabled
+	xor a
+	ld [hOAMBufferOffset], a
+
+.spriteLoop
+	ld [hSpriteOffset2], a
+
+	ld d, wSpriteStateData1 / $100
+	ld a, [hSpriteOffset2]
+	ld e, a
+	ld a, [de] ; c1x0
+	and a
+	jp z, .nextSprite
+
+	inc e
+	inc e
+	ld a, [de] ; c1x2 (facing/anim)
+	ld [wd5cd], a
+	cp $ff ; off-screen (don't draw)
+	jr nz, .visible
+
+	call GetSpriteScreenXY
+	jr .nextSprite
+
+.visible
+	cp $a0 ; is the sprite unchanging like an item ball or boulder?
+	jr c, .usefacing
+
+; unchanging
+	and $f
+	add $10 ; skip to the second half of the table which doesn't account for facing direction
+	jr .next
+
+.usefacing
+	and $f
+
+.next
+	ld l, a
+
+; get sprite priority
+	push de
+	inc d
+	ld a, e
+	add $5
+	ld e, a
+	ld a, [de] ; c2x7
+	and $80
+	ld [hSpritePriority], a ; temp store sprite priority
+	pop de
+
+; read the entry from the table
+	ld h, 0
+	ld bc, SpriteFacingAndAnimationTable
+	add hl, hl
+	add hl, hl
+	add hl, bc
+	ld a, [hli]
+	ld c, a
+	ld a, [hli]
+	ld b, a
+	ld a, [hli]
+	ld h, [hl]
+	ld l, a
+
+	call GetSpriteScreenXY
+
+	ld a, [hOAMBufferOffset]
+	ld e, a
+	ld d, wOAMBuffer / $100
+
+.tileLoop
+	ld a, [hSpriteScreenY]   ; temp for sprite Y position
+	add $10                  ; Y=16 is top of screen (Y=0 is invisible)
+	add [hl]                 ; add Y offset from table
+	ld [de], a               ; write new sprite OAM Y position
+	inc hl
+	ld a, [hSpriteScreenX]   ; temp for sprite X position
+	add $8                   ; X=8 is left of screen (X=0 is invisible)
+	add [hl]                 ; add X offset from table
+	inc e
+	ld [de], a               ; write new sprite OAM X position
+	inc e
+	ld a, [bc]               ; read pattern number offset (accommodates orientation (offset 0,4 or 8) and animation (offset 0 or $80))
+	inc bc
+	push bc
+	ld b, a
+
+	ld a, [wd5cd]            ; temp copy of c1x2
+	swap a                   ; high nybble determines sprite used (0 is always player sprite, next are some npcs)
+	and $f
+
+	; Sprites $a and $b have one face (and therefore 4 tiles instead of 12).
+	; As a result, sprite $b's tile offset is less than normal.
+	cp $b
+	jr nz, .notFourTileSprite
+	ld a, $a * 12 + 4
+	jr .next2
+
+.notFourTileSprite
+	; a *= 12
+	sla a
+	sla a
+	ld c, a
+	sla a
+	add c
+
+.next2
+	add b ; add the tile offset from the table (based on frame and facing direction)
+	pop bc
+	ld [de], a ; tile id
+	inc hl
+	inc e
+	ld a, [hl]
+	bit 1, a ; is the tile allowed to set the sprite priority bit?
+	jr z, .skipPriority
+	ld a, [hSpritePriority]
+	or [hl]
+.skipPriority
+	inc hl
+	ld [de], a
+	inc e
+	bit 0, a ; OAMFLAG_ENDOFDATA
+	jr z, .tileLoop
+
+	ld a, e
+	ld [hOAMBufferOffset], a
+
+.nextSprite
+	ld a, [hSpriteOffset2]
+	add $10
+	cp $100 % $100
+	jp nz, .spriteLoop
+
+	; Clear unused OAM.
+	ld a, [hOAMBufferOffset]
+	ld l, a
+	ld h, wOAMBuffer / $100
+	ld de, $4
+	ld b, $a0
+	ld a, [wd736]
+	bit 6, a ; jumping down ledge or fishing animation?
+	ld a, $a0
+	jr z, .clear
+
+; Don't clear the last 4 entries because they are used for the shadow in the
+; jumping down ledge animation and the rod in the fishing animation.
+	ld a, $90
+
+.clear
+	cp l
+	ret z
+	ld [hl], b
+	add hl, de
+	jr .clear
+
+GetSpriteScreenXY:
+	inc e
+	inc e
+	ld a, [de] ; c1x4
+	ld [hSpriteScreenY], a
+	inc e
+	inc e
+	ld a, [de] ; c1x6
+	ld [hSpriteScreenX], a
+	ld a, 4
+	add e
+	ld e, a
+	ld a, [hSpriteScreenY]
+	add 4
+	and $f0
+	ld [de], a ; c1xa (y)
+	inc e
+	ld a, [hSpriteScreenX]
+	and $f0
+	ld [de], a  ; c1xb (x)
+	ret