better oam code

PrepareOAMData: ; 499b (1:499b)
; Determine OAM data for currently visible
; sprites and write it to wOAMBuffer.
; Yellow code has been changed to use registers more efficiently
; as well as tweaking the code to show gbc palettes

    ld a, [wUpdateSpritesEnabled]
    dec a
    jr z, .updateEnabled

    cp $ff
    ret nz
    ld [wUpdateSpritesEnabled], a
    jp HideSprites

.updateEnabled
    xor a
    ld [hOAMBufferOffset], a

.spriteLoop
    ld [hSpriteOffset2], a

    ld e, a
    ld d, wSpriteStateData1 / $100

    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
    xor a
    jr .next

.usefacing
    and $f

.next
; read the entry from the table
    add a
    ld c, a
    ld b, 0
    ld hl, SpriteFacingAndAnimationTable
    add hl, bc
    ld a, [hli]
    ld h, [hl]
    ld l, a
; get sprite priority
    ld b, d
    ld c, e

    inc b
    ld a, c
    add $5
    ld c, a
    ld a, [bc] ; c2x7
    and $80
    ld [hSpritePriority], a ; temp store sprite priority

    call GetSpriteScreenXY

    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 ; $7c
    jr .startTileLoop

.notFourTileSprite
    ; a *= 12
    add a
    add a
    ld c, a
    add a
    add c
.startTileLoop
    ld b, a

    ld a, [hOAMBufferOffset]
    ld e, a
    ld d, wOAMBuffer / $100

    ld c, $4
.loop
    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
    inc e
    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
    ld [de], a
    inc hl
    inc e
    ld a, [hli]
    add b
    ld [de], a ; tile id
    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
; uncomment the following range for pal conversion
;   and $f0
;   bit 4, a ; OBP0 or OBP1
;   jr z, .spriteusesOBP0
;   or %100 ; palettes 4-7 are OBP1
;.spriteusesOBP0
    ld [de], a
    inc hl
    inc e
    dec c
    jr nz, .loop

    ld a, e
    ld [hOAMBufferOffset], a
.nextSprite
    ld a, [hSpriteOffset2]
    add $10
    jp nz, .spriteLoop

    ; Clear unused OAM.
    ld a, [wd736]
    bit 6, a ; jumping down ledge or fishing animation?
    ld c, $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 c, $90

.clear
    ld a, [hOAMBufferOffset]
    cp c
    ret nc
    ld l, a
    ld h, wOAMBuffer / $100

    ld de, $4 ; entry size
    ld b, $a0
.clearLoop
    ld [hl], b
    add hl, de
    cp l
    jr nz, .clearLoop
    ret

GetSpriteScreenXY: ; 4a5f (1:4a5f)
    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

======================================================================

SpriteFacingAndAnimationTable: ; 4000 (1:4000)
    dw SpriteFacingDownAndStanding        ; facing down, walk animation frame 0
    dw SpriteFacingDownAndWalking         ; facing down, walk animation frame 1
    dw SpriteFacingDownAndStanding        ; facing down, walk animation frame 2
    dw SpriteFacingDownAndWalking2        ; facing down, walk animation frame 3

    dw SpriteFacingUpAndStanding          ; facing up, walk animation frame 0
    dw SpriteFacingUpAndWalking           ; facing up, walk animation frame 1
    dw SpriteFacingUpAndStanding          ; facing up, walk animation frame 2
    dw SpriteFacingUpAndWalking2          ; facing up, walk animation frame 3

    dw SpriteFacingLeftAndStanding        ; facing left, walk animation frame 0
    dw SpriteFacingLeftAndWalking         ; facing left, walk animation frame 1
    dw SpriteFacingLeftAndStanding        ; facing left, walk animation frame 2
    dw SpriteFacingLeftAndWalking         ; facing left, walk animation frame 3

    dw SpriteFacingRightAndStanding       ; facing right, walk animation frame 0
    dw SpriteFacingRightAndWalking        ; facing right, walk animation frame 1
    dw SpriteFacingRightAndStanding       ; facing right, walk animation frame 2
    dw SpriteFacingRightAndWalking        ; facing right, walk animation frame 3

    dw SpriteFacingDownAndStanding        ; ---
    dw SpriteFacingDownAndStanding        ; This table is used for sprites $a and $b.
    dw SpriteFacingDownAndStanding        ; All orientation and animation parameters
    dw SpriteFacingDownAndStanding        ; lead to the same result. Used for immobile
    dw SpriteFacingDownAndStanding        ; sprites like items on the ground
    dw SpriteFacingDownAndStanding        ; ---
    dw SpriteFacingDownAndStanding
    dw SpriteFacingDownAndStanding
    dw SpriteFacingDownAndStanding
    dw SpriteFacingDownAndStanding
    dw SpriteFacingDownAndStanding
    dw SpriteFacingDownAndStanding
    dw SpriteFacingDownAndStanding
    dw SpriteFacingDownAndStanding
    dw SpriteFacingDownAndStanding
    dw SpriteFacingDownAndStanding

SpriteFacingDownAndStanding: ; 4042 (1:4042)
; Sprite OAM Parameters
    db $00,$00,$00,$00                                      ; top left
    db $00,$08,$01,$00                                      ; top right
    db $08,$00,$02,OAMFLAG_CANBEMASKED                      ; bottom left
    db $08,$08,$03,OAMFLAG_CANBEMASKED | OAMFLAG_ENDOFDATA  ; bottom right

SpriteFacingDownAndWalking: ; 4053 (1:4053)
; Sprite OAM Parameters
    db $00,$00,$80,$00                                      ; top left
    db $00,$08,$81,$00                                      ; top right
    db $08,$00,$82,OAMFLAG_CANBEMASKED                      ; bottom left
    db $08,$08,$83,OAMFLAG_CANBEMASKED | OAMFLAG_ENDOFDATA  ; bottom right

SpriteFacingDownAndWalking2: ; 4064 (1:4064)
; Sprite OAM Parameters
    db $00,$08,$80,OAMFLAG_VFLIPPED                                           ; top left
    db $00,$00,$81,OAMFLAG_VFLIPPED                                           ; top right
    db $08,$08,$82,OAMFLAG_VFLIPPED | OAMFLAG_CANBEMASKED                     ; bottom left
    db $08,$00,$83,OAMFLAG_VFLIPPED | OAMFLAG_CANBEMASKED | OAMFLAG_ENDOFDATA ; bottom right

SpriteFacingUpAndStanding: ; 4075 (1:4075)
; Sprite OAM Parameters
    db $00,$00,$04,$00                                      ; top left
    db $00,$08,$05,$00                                      ; top right
    db $08,$00,$06,OAMFLAG_CANBEMASKED                      ; bottom left
    db $08,$08,$07,OAMFLAG_CANBEMASKED | OAMFLAG_ENDOFDATA  ; bottom right

SpriteFacingUpAndWalking: ; 4086 (1:4086)
; Sprite OAM Parameters
    db $00,$00,$84,$00                                      ; top left
    db $00,$08,$85,$00                                      ; top right
    db $08,$00,$86,OAMFLAG_CANBEMASKED                      ; bottom left
    db $08,$08,$87,OAMFLAG_CANBEMASKED | OAMFLAG_ENDOFDATA  ; bottom right

SpriteFacingUpAndWalking2: ; 4097 (1:4097)
; Sprite OAM Parameters
    db $00,$08,$84,OAMFLAG_VFLIPPED                                           ; top left
    db $00,$00,$85,OAMFLAG_VFLIPPED                                           ; top right
    db $08,$08,$86,OAMFLAG_VFLIPPED | OAMFLAG_CANBEMASKED                     ; bottom left
    db $08,$00,$87,OAMFLAG_VFLIPPED | OAMFLAG_CANBEMASKED | OAMFLAG_ENDOFDATA ; bottom right

SpriteFacingLeftAndStanding: ; 40a8 (1:40a8)
; Sprite OAM Parameters
    db $00,$00,$08,$00                                      ; top left
    db $00,$08,$09,$00                                      ; top right
    db $08,$00,$0a,OAMFLAG_CANBEMASKED                      ; bottom left
    db $08,$08,$0b,OAMFLAG_CANBEMASKED | OAMFLAG_ENDOFDATA  ; bottom right

SpriteFacingLeftAndWalking: ; 40b9 (1:40b9)
; Sprite OAM Parameters
    db $00,$00,$88,$00                                      ; top left
    db $00,$08,$89,$00                                      ; top right
    db $08,$00,$8a,OAMFLAG_CANBEMASKED                      ; bottom left
    db $08,$08,$8b,OAMFLAG_CANBEMASKED | OAMFLAG_ENDOFDATA  ; bottom right

SpriteFacingRightAndStanding: ; 40ca (1:40ca)
; Sprite OAM Parameters
    db $00,$08,$08,OAMFLAG_VFLIPPED                                           ; top left
    db $00,$00,$09,OAMFLAG_VFLIPPED                                           ; top right
    db $08,$08,$0a,OAMFLAG_VFLIPPED | OAMFLAG_CANBEMASKED                     ; bottom left
    db $08,$00,$0b,OAMFLAG_VFLIPPED | OAMFLAG_CANBEMASKED | OAMFLAG_ENDOFDATA ; bottom right

SpriteFacingRightAndWalking: ; 40db (1:40db)
; Sprite OAM Parameters
    db $00,$08,$88,OAMFLAG_VFLIPPED                                           ; top left
    db $00,$00,$89,OAMFLAG_VFLIPPED                                           ; top right
    db $08,$08,$8a,OAMFLAG_VFLIPPED | OAMFLAG_CANBEMASKED                     ; bottom left
    db $08,$00,$8b,OAMFLAG_VFLIPPED | OAMFLAG_CANBEMASKED | OAMFLAG_ENDOFDATA ; bottom right