; Graphic screen initialization
InitGraphics
                jsr   ShadowOn
                jsr   GrafOn
                lda   #0
                jsr   ClearToColor
                lda   #0
                jsr   SetSCBs
                ldx   #DefaultPalette
                lda   #0
                jsr   SetPalette
                rts

DefaultPalette  dw    $0000,$007F,$0090,$0FF0
                dw    $000F,$0080,$0f70,$0FFF
                dw    $0fa9,$0ff0,$00e0,$04DF
                dw    $0d00,$078f,$0ccc,$0FFF

; Return the current border color ($0 - $F) in the accumulator
GetBorderColor  lda   #0000
                sep   #$20
                ldal  BORDER_REG
                and   #$0F
                rep   #$20
                rts

; Set the border color to the accumulator value.
SetBorderColor  sep   #$20                 ; ACC = $X_Y, REG = $W_Z
                eorl  BORDER_REG           ; ACC = $(X^Y)_(Y^Z)
                and   #$0F                 ; ACC = $0_(Y^Z)
                eorl  BORDER_REG           ; ACC = $W_(Y^Z^Z) = $W_Y
                stal  BORDER_REG
                rep   #$20
                rts

; Clear to SHR screen to a specific color
ClearToColor    ldx   #$7D00               ;start at top of pixel data! ($2000-9D00)
:clearloop      dex
                dex
                stal  SHR_SCREEN,x         ;screen location
                bne   :clearloop           ;loop until we've worked our way down to 0
                rts

; Set a palette values
; A = palette number, X = palette address
SetPalette
                and   #$000F               ; palette values are 0 - 15 and each palette is 32 bytes
                asl
                asl
                asl
                asl
                asl
                txy
                tax

]idx            equ   0
                lup   16
                lda:  $0000+]idx,y
                stal  SHR_PALETTES+]idx,x
]idx            equ   ]idx+2
                --^
                rts

; Initialize the SCB
SetSCBs         ldx   #$0100               ;set all $100 scbs to A
:scbloop        dex
                dex
                stal  SHR_SCB,x
                bne   :scbloop
                rts

; Turn SHR screen On/Off
GrafOn          sep   #$20
                lda   #$81
                stal  NEW_VIDEO_REG
                rep   #$20
                rts

GrafOff         sep   #$20
                lda   #$01
                stal  NEW_VIDEO_REG
                rep   #$20
                rts

; Enable/Disable Shadowing.
ShadowOn        sep   #$20
                ldal  SHADOW_REG
                and   #$F7
                stal  SHADOW_REG
                rep   #$20
                rts

ShadowOff       sep   #$20
                ldal  SHADOW_REG
                ora   #$08
                stal  SHADOW_REG
                rep   #$20
                rts

GetVBL          sep   #$20
                ldal  VBL_HORZ_REG
                asl
                ldal  VBL_VERT_REG
                rol                        ; put V5 into carry bit, if needed. See TN #39 for details.
                rep   #$20
                and   #$00FF
                rts

WaitForVBL      sep   #$20
:wait1          ldal  VBL_STATE_REG        ; If we are already in VBL, then wait
                bmi   :wait1
:wait2          ldal  VBL_STATE_REG
                bpl   :wait2               ; spin until transition into VBL
                rep   #$20
                rts